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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="asio.history"></a><a class="link" href="history.html" title="Revision History">Revision History</a>
</h2></div></div></div>
<h4>
<a name="asio.history.h0"></a>
      <span><a name="asio.history.asio_1_18_1"></a></span><a class="link" href="history.html#asio.history.asio_1_18_1">Asio
      1.18.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Enabled support for UNIX domain sockets on Windows. From Windows 10, UNIX
          domain sockets (a.k.a "local" sockets) are supported on Windows,
          with the exception of the <code class="computeroutput">connect_pair</code> function (which will
          fail with an operation_not_supported error).
        </li>
<li class="listitem">
          Added executor-converting construction and assignment to <code class="computeroutput">ip::basic_resolver</code>.
        </li>
<li class="listitem">
          Added compatibility between polymorphic executors and the (deprecated)
          handler invocation hook.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">experimental::as_single</code> completion token adapter.
          The <code class="computeroutput">as_single</code> completion token adapter can be used to specify
          that the completion handler arguments should be combined into a single
          argument. For completion signatures with a single parameter, the argument
          is passed through as-is. For signatures with two or more parameters, the
          arguments are combined into a tuple. The <code class="computeroutput">as_single</code> adapter
          may be used in conjunction with <code class="computeroutput">use_awaitable</code> and structured
          bindings as follows:<br>
<pre class="programlisting">auto [e, n] = co_await socket.async_read_some(
    asio::buffer(data), as_single(use_awaitable));
</pre>
          <br> Alternatively, it may be used as a default completion token like
          so:<br>
<pre class="programlisting">using default_token = as_single_t&lt;use_awaitable_t&lt;&gt;&gt;;
using tcp_socket = default_token::as_default_on_t&lt;tcp::socket&gt;;
// ...
awaitable&lt;void&gt; do_read(tcp_socket socket)
{
  // ...
  auto [e, n] = co_await socket.async_read_some(asio::buffer(data));
  // ...
}
</pre>
          <br>
        </li>
<li class="listitem">
          Added support for <code class="computeroutput">MSG_NOSIGNAL</code> on more platforms by using
          <code class="computeroutput">_POSIX_VERSION</code> to detect whether it is supported.
        </li>
<li class="listitem">
          Added the ability to compile using libpthread on Windows.
        </li>
<li class="listitem">
          Added workarounds for the Intel C++ compiler.
        </li>
<li class="listitem">
          Added more support for detecting and optimising for handlers that have
          no custom executor.
        </li>
<li class="listitem">
          Reduced lock contention for timer cancellation on Windows.
        </li>
<li class="listitem">
          Reinstated a previously removed null-pointer check, as it had a measurable
          impact on performance.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">executor</code> concept to test for a const-qualified
          <code class="computeroutput">execute()</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">any_executor</code> support for builds without RTTI support.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">thread_pool</code> unit test to work without RTTI support.
        </li>
<li class="listitem">
          Fixed C++20 coroutines compatibility with clang on Windows.
        </li>
<li class="listitem">
          Fixed some compatibility issues with Windows Runtime.
        </li>
<li class="listitem">
          Fixed shadow name warnings caused by addition of <code class="computeroutput">asio::query</code>.
        </li>
<li class="listitem">
          Fixed a "logical ‘or’ of equal expressions" warning on linux.
        </li>
<li class="listitem">
          Fixed a benign switch fallthrough warning.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput">push/pop_options.hpp</code> includes.
        </li>
<li class="listitem">
          Suppressed zero-as-null-pointer-constant warnings.
        </li>
<li class="listitem">
          Fixed a comma-operator warning.
        </li>
<li class="listitem">
          Updated the documentation to clarify when the <code class="literal">select</code>
          reactor is used on Windows.
        </li>
<li class="listitem">
          Fixed potential ambiguity caused by <code class="computeroutput">any_executor</code> comparisons
          and conversion.
        </li>
<li class="listitem">
          Added detection of non-experimental C++20 coroutines on MSVC 19.8.
        </li>
<li class="listitem">
          Fixed compatibility with uClibc.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">strand&lt;&gt;</code> adaptation of Networking TS executors
          when targeting older C++ versions or less conformant compilers.
        </li>
</ul></div>
<h4>
<a name="asio.history.h1"></a>
      <span><a name="asio.history.asio_1_18_0"></a></span><a class="link" href="history.html#asio.history.asio_1_18_0">Asio
      1.18.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Marked the <code class="computeroutput">basic_socket_acceptor</code> move constructor as <code class="computeroutput">noexcept</code>.
        </li>
<li class="listitem">
          Added workarounds for various issues in <code class="literal">gcc</code> 10's coroutine
          support.
        </li>
<li class="listitem">
          Added standard executor support to <code class="computeroutput">windows::overlapped_ptr</code>.
        </li>
<li class="listitem">
          Added missing compatibility macros for the <code class="computeroutput">execution::receiver_of</code>
          concept.
        </li>
<li class="listitem">
          Added short-circuited evaluation to <code class="computeroutput">execution::executor</code>,
          <code class="computeroutput">execution::operation_state</code>,<code class="computeroutput">execution::sender</code>,
          <code class="computeroutput">execution::receiver</code>, <code class="computeroutput">execution::receiver_of</code>,
          and <code class="computeroutput">execution::scheduler</code> concepts and the corresponding traits.
          These now test first for well-formed CPO expressions (or, in the case of
          senders, a specialised <code class="computeroutput">sender_traits</code> template) and, if not
          valid, short-circuit the remainder of the evaluation. This helps prevent
          recursive template instantiations that can occur in some contexts.
        </li>
<li class="listitem">
          Added constraints to the <code class="computeroutput">strand</code> template's constructor, to
          prevent template instantiation recursion.
        </li>
<li class="listitem">
          Changed Asio's internal executor adapters to prevent template instantiation
          recursion.
        </li>
<li class="listitem">
          Added constraints to the <code class="computeroutput">execution::any_executor</code> template's
          converting constructors, as per the specification.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput">execution::sender_traits</code> specialisation and
          <code class="computeroutput">connect()</code> member function to the <code class="computeroutput">thread_pool</code>
          executor, as per the specification.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">execution::blocking_t::always_t::is_preferable</code> to
          be false as per the specification.
        </li>
<li class="listitem">
          Added <code class="computeroutput">shape_type</code> and <code class="computeroutput">index_type</code> to <code class="computeroutput">thread_pool</code>
          executors, as per the specification.
        </li>
<li class="listitem">
          Ensured that the standard executor concept-related traits (such as <code class="computeroutput">execution::is_executor</code>)
          work with <code class="computeroutput">void</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">async_compose</code> support for standard executors.
        </li>
<li class="listitem">
          Fixed the forward declaration of <code class="computeroutput">any_io_executor</code> in <code class="literal">asio/ts/netfwd.hpp</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">use_future</code> compatibility with older compilers.
        </li>
<li class="listitem">
          Fixed compatibility with MinGW.
        </li>
<li class="listitem">
          Improved compatibility with older versions of <code class="literal">gcc</code>.
        </li>
<li class="listitem">
          Added compatiblity with <code class="literal">clang-cl</code> on Windows.
        </li>
<li class="listitem">
          Fixed various compiler warnings.
        </li>
<li class="listitem">
          Added basic overview documentation for the standard executors support.
        </li>
<li class="listitem">
          Added detailed descriptions to the standard executor-related member functions
          of <code class="computeroutput">io_context</code> executors, <code class="computeroutput">thread_pool</code> executors,
          <code class="computeroutput">system_executor</code>, and <code class="computeroutput">strand&lt;&gt;</code>.
        </li>
<li class="listitem">
          Changed introductory documentation to reflect that there our now multiple
          types of I/O execution context.
        </li>
<li class="listitem">
          Marked constructors, destructors, and static data members in class synopses
          in the reference documentation.
        </li>
<li class="listitem">
          Fixed various minor documentation errors.
        </li>
</ul></div>
<h4>
<a name="asio.history.h2"></a>
      <span><a name="asio.history.asio_1_17_0"></a></span><a class="link" href="history.html#asio.history.asio_1_17_0">Asio
      1.17.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added an implementation of the proposed standard executors (<a href="http://wg21.link/P0443r13" target="_top">P0443r13</a>,
          <a href="http://wg21.link/P1348r0" target="_top">P1348r0</a>, and <a href="http://wg21.link/P1393r0" target="_top">P1393r0</a>).
        </li>
<li class="listitem">
          Added support for the proposed standard executors to Asio's I/O facilities:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                The <code class="computeroutput">io_context::executor_type</code>, <code class="computeroutput">thread_pool::executor_type</code>,
                <code class="computeroutput">system_executor</code>, and <code class="computeroutput">strand</code> executors now
                meet the requirements for the proposed standard executors. These
                classes also continue to meet the existing requirements for the Networking
                TS model of executors.
              </li>
<li class="listitem">
                All I/O objects, asynchronous operations, and utilities including
                <code class="computeroutput">dispatch</code>, <code class="computeroutput">post</code>, <code class="computeroutput">defer</code>, <code class="computeroutput">get_associated_executor</code>,
                <code class="computeroutput">bind_executor</code>, <code class="computeroutput">make_work_guard</code>, <code class="computeroutput">spawn</code>,
                <code class="computeroutput">co_spawn</code>, <code class="computeroutput">async_compose</code>, <code class="computeroutput">use_future</code>,
                etc., can interoperate with both new proposed standard executors,
                and with existing Networking TS executors. The implementation determines
                at compile time which model a particular executor meets; the proposed
                standard executor model is used in preference if both are detected.
              </li>
<li class="listitem">
                The <code class="computeroutput">any_io_executor</code> type alias has been introduced as
                the new default runtime-polymorphic executor for all I/O objects.
                This type alias points to the <code class="computeroutput">execution::any_executor&lt;&gt;</code>
                template with a set of supportable properties specified for use with
                I/O. This change may break existing code that directly uses the old
                polymorphic wrapper, <code class="computeroutput">executor</code>. If required for backward
                compatibility, <code class="computeroutput">ASIO_USE_TS_EXECUTOR_AS_DEFAULT</code> can be
                defined, which changes the <code class="computeroutput">any_io_executor</code> type alias
                to instead point to the <code class="computeroutput">executor</code> polymorphic wrapper.
              </li>
<li class="listitem">
                Support for the existing Networking TS model of executors can be
                disabled by defining <code class="computeroutput">ASIO_NO_TS_EXECUTORS</code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added converting move construction and assignment to <code class="computeroutput">basic_waitable_timer</code>.
          This enables move construction and assignment between different timer types,
          provided the executor types are convertible. For example:<br>
<pre class="programlisting">basic_waitable_timer&lt;
    clock_type,
    traits_type,
    io_context::executor_type
  &gt; timer1(my_io_context);

basic_waitable_timer&lt;
    clock_type,
    traits_type,
    any_io_executor // polymorphic wrapper
  &gt; timer2(std::move(timer1));
</pre>
          <br>
        </li>
<li class="listitem">
          Enabled C++20 coroutine support when using <code class="literal">gcc</code> 10.
        </li>
<li class="listitem">
          Added overloads of <code class="computeroutput">co_spawn</code> that launch an awaitable. This
          change allows us to write:<br>
<pre class="programlisting">co_spawn(executor,
    echo(std::move(socket)),
    detached);
</pre>
          <br> instead of:<br>
<pre class="programlisting">co_spawn(executor,
    [socket = std::move(socket)]() mutable
    {
      return echo(std::move(socket));
    },
    detached);
</pre>
          <br>
        </li>
<li class="listitem">
          Added a new constructor overload to <code class="computeroutput">use_awaitable_t</code>'s default
          executor adapter, to enable conversion between executor types.
        </li>
<li class="listitem">
          Added support for using <code class="computeroutput">detached_t</code> as a default completion
          token, by adding members <code class="computeroutput">as_default_on()</code> and <code class="computeroutput">as_default_on_t&lt;&gt;</code>.
        </li>
<li class="listitem">
          Added a move constructor to <code class="computeroutput">ssl::stream&lt;&gt;</code>.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">ssl::stream&lt;&gt;</code> write operations to linearise
          gather-write buffer sequences.
        </li>
<li class="listitem">
          Added compile-time detection of the deprecated <code class="computeroutput">asio_handler_invoke</code>
          hook. This hook was deprecated with the introduction of the Networking
          TS trait <code class="computeroutput">associated_executor</code> and function <code class="computeroutput">get_associated_executor()</code>.
          Compiling an application with <code class="computeroutput">ASIO_NO_DEPRECATED</code> will now
          trigger a compile error if any handler implements the <code class="computeroutput">asio_handler_invoke</code>
          hook.
        </li>
<li class="listitem">
          Added compile-time detection of the deprecated <code class="computeroutput">asio_handler_allocate</code>
          and <code class="computeroutput">asio_handle_deallocate</code> hooks. These hooks were deprecated
          with the introduction of the Networking TS trait <code class="computeroutput">associated_allocator</code>
          and function <code class="computeroutput">get_associated_allocator()</code>. Compiling an application
          with <code class="computeroutput">ASIO_NO_DEPRECATED</code> will now trigger a compile error if
          any handler implements the <code class="computeroutput">asio_handler_allocate</code> or <code class="computeroutput">asio_handler_deallocate</code>
          hooks.
        </li>
<li class="listitem">
          Implemented a number of performance optimisations, including:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Specialising single-buffer operations to use <code class="computeroutput">recv</code> rather
                than <code class="computeroutput">recvmsg</code>, <code class="computeroutput">send</code> rather than <code class="computeroutput">sendmsg</code>,
                <code class="computeroutput">read</code> rather than <code class="computeroutput">readv</code>, and <code class="computeroutput">write</code>
                rather than <code class="computeroutput">writev</code>.
              </li>
<li class="listitem">
                Lightening the reference counting overhead of the polymorphic wrapper
                <code class="computeroutput">executor</code>.
              </li>
<li class="listitem">
                Returning from system call operation wrappers as early as possible,
                and only accessing <code class="computeroutput">errno</code> and error codes when on an
                error path.
              </li>
<li class="listitem">
                Applying additional optimisations if a "native" I/O executor
                (such as <code class="computeroutput">io_context::exeutor_type</code>) is detected.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added source location support to handler tracking. The new <code class="computeroutput">ASIO_HANDLER_LOCATION((file_name,
          line, function_name))</code> macro may be used to inform the handler tracking
          mechanism of a source location. This macro declares an object that is placed
          on the stack. Then, when an asynchronous operation is launched with location
          information, it outputs lines using the <span class="bold"><strong>&lt;action&gt;</strong></span>
          <code class="literal">n^m</code>, prior to the <code class="literal">n*m</code> line that signifies
          the beginning of the asynchronous operation. For example:
<pre class="programlisting">@asio|1589423304.861944|&gt;7|ec=system:0,bytes_transferred=5
@asio|1589423304.861952|7^8|in 'async_write' (./../../../include/asio/impl/write.hpp:330)
@asio|1589423304.861952|7^8|called from 'do_write' (handler_tracking/async_tcp_echo_server.cpp:62)
@asio|1589423304.861952|7^8|called from 'operator()' (handler_tracking/async_tcp_echo_server.cpp:51)
@asio|1589423304.861952|7*8|socket@0x7ff61c008230.async_send
@asio|1589423304.861975|.8|non_blocking_send,ec=system:0,bytes_transferred=5
@asio|1589423304.861980|&lt;7|
</pre>
          <br> If <code class="computeroutput">std::source_location</code> or <code class="computeroutput">std::experimental::source_location</code>
          are available, the <code class="computeroutput">use_awaitable_t</code> token (when default-constructed
          or used as a default completion token) will also cause handler tracking
          to output a source location for each newly created asynchronous operation.
          A <code class="computeroutput">use_awaitable_t</code> object may also be explicitly constructed
          with location information.
        </li>
<li class="listitem">
          Implemented various improvements to the <code class="literal">handlerviz.pl</code>
          tool.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Add nodes for pending handlers at bottom of graph, outlined in red.
              </li>
<li class="listitem">
                Display source location in a tooltip on the edge label (for SVG).
              </li>
<li class="listitem">
                Use invisible nodes to enforce order to keep related control flow
                vertical.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added the <code class="literal">handlerlive.pl</code> tool, which processes handler
          tracking output to produce a list of "live" handlers. Live handlers
          are those that are associated with pending asynchronous operations, as
          well as handlers that are currently executing. For example:
<pre class="programlisting">cat output.txt | perl handlerlive.pl
</pre>
          or:
<pre class="programlisting">perl handerlive.pl &lt; output.txt
</pre>
          or:
<pre class="programlisting">perl handlerlive.pl output.txt
</pre>
          <br>
        </li>
<li class="listitem">
          Added the <code class="literal">handlertree.pl</code> tool, which filters handler
          tracking output to include only those events in the tree that produced
          the nominated handlers. For example, to filter the output to include only
          the events associated with handlers <code class="computeroutput">123</code>, <code class="computeroutput">456</code>,
          and their predecessors:
<pre class="programlisting">cat output.txt | perl handlertree.pl 123 456
</pre>
          or:
<pre class="programlisting">perl handlertree.pl 123 456 &lt; output.txt
</pre>
          <br> This script may be combined with handerlive.pl and handlerviz.pl
          to produce a graph of the "live" asynchronous operation chains.
          For example:
<pre class="programlisting">cat output.txt | \
  perl handlertree.pl `perl handlerlive.pl output.txt` | \
  perl handlerviz.pl | \
  dot -Tsvg &gt; output.svg
</pre>
          <br>
        </li>
<li class="listitem">
          Added changes for clang-based Embarcadero C++ compilers.
        </li>
<li class="listitem">
          Fixed a deadlock that can occur when multiple threads concurrently initialise
          the Windows I/O completion port backend.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">async_compose</code> to work with copyable handlers when passed
          by lvalue.
        </li>
<li class="listitem">
          Fixed completion signature deduction in <code class="computeroutput">co_spawn</code>.
        </li>
<li class="listitem">
          Removed a spurious <code class="computeroutput">Executor</code> base class from the <code class="computeroutput">executor_binder</code>
          implementation.
        </li>
<li class="listitem">
          Various fixes and improvements in the documentation and examples.
        </li>
</ul></div>
<h4>
<a name="asio.history.h3"></a>
      <span><a name="asio.history.asio_1_16_1"></a></span><a class="link" href="history.html#asio.history.asio_1_16_1">Asio
      1.16.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed compatibility with C++20 concept syntax.
        </li>
<li class="listitem">
          Marked the POSIX descriptor classes' move constructors as <code class="computeroutput">noexcept</code>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">ssl::host_name_verification</code> class, which is a drop-in
          replacement for <code class="computeroutput">ssl::rfc2818_verification</code>. The <code class="computeroutput">ssl::rfc2818_verification</code>
          class has been marked as deprecated. As a consequence of this change, SSL
          support now depends on functions that were introduced in OpenSSL 1.0.2.
        </li>
<li class="listitem">
          Added an <code class="computeroutput">ssl::context</code> constructor to take ownership of a native
          handle.
        </li>
<li class="listitem">
          Changed C++ language version detection with <code class="literal">gcc</code> to use
          <code class="computeroutput">__cplusplus</code> macro.
        </li>
<li class="listitem">
          Fixed a work counting issue in the asynchronous resolve operation for endpoints.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">strand&lt;&gt;</code> converting constructors and assignment
          operators.
        </li>
<li class="listitem">
          Ensured that resolvers are restarted correctly after a fork.
        </li>
<li class="listitem">
          Fixed compatibility with the current NetBSD release.
        </li>
<li class="listitem">
          Removed spurious handler requirement checks in some <code class="computeroutput">async_read</code>
          overloads.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">ssl::context</code> class to propagate non-EOF errors
          from the <code class="computeroutput">add_certificate_authority</code> function.
        </li>
<li class="listitem">
          Fixed a Windows-specific <code class="computeroutput">thread_pool</code> destructor hang that
          occurred when the pool had an associated I/O object.
        </li>
<li class="listitem">
          Changed the <code class="literal">select</code> reactor to recreate the "self
          pipe trick" sockets on error. This addresses an issue on some versions
          of Windows, where these sockets are discconected after a system sleep.
        </li>
<li class="listitem">
          Fixed a compile error in the buffered streams due to the lack of reference
          collapsing in C++98.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">priority_scheduler</code> example to demonstrate calls
          to <code class="computeroutput">shutdown()</code> and <code class="computeroutput">destroy()</code>.
        </li>
<li class="listitem">
          Removed some unnecessary null pointer checks.
        </li>
<li class="listitem">
          Changed Windows platform detection to recognise TV titles as Windows apps.
        </li>
<li class="listitem">
          Added some emscripten compatibility patches.
        </li>
<li class="listitem">
          Fixed a compile error in the <code class="computeroutput">use_awaitable_t::as_default_on</code>
          function.
        </li>
<li class="listitem">
          Changed all uses of the boost.bind placeholders to use the <code class="computeroutput">boost::placeholders</code>
          namespace.
        </li>
<li class="listitem">
          Fixed a potential compile error in the <code class="computeroutput">async_compose</code> implementation
          due to incorrect overload selection.
        </li>
<li class="listitem">
          Suppressed some non-virtual destructor warnings.
        </li>
<li class="listitem">
          Various documentation fixes and improvements.
        </li>
</ul></div>
<h4>
<a name="asio.history.h4"></a>
      <span><a name="asio.history.asio_1_16_0"></a></span><a class="link" href="history.html#asio.history.asio_1_16_0">Asio
      1.16.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Changed the <code class="computeroutput">async_initiate</code> helper function to automatically
          deduce its return type. This is enabled for C++11 or later.
        </li>
<li class="listitem">
          Changed all asynchronous operations to use automatically deduced return
          types. This allows completion token implementations to incorporate the
          asynchronous operation initiation into the initiating function's return
          type, without type erasure. Note that C++14 or later is required to support
          completion tokens that use per-operation return type deduction. For C++11
          or earlier, a completion token's async_result specialisation must still
          provide the nested typedef <code class="computeroutput">return_type</code>.
        </li>
<li class="listitem">
          Introduced three new concepts to support <code class="computeroutput">async_initiate</code>.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                <code class="computeroutput">completion_signature&lt;T&gt;</code>: Checks if <code class="computeroutput">T</code>
                is a signature of the form <code class="computeroutput">R(Args...)</code>.
              </li>
<li class="listitem">
                <code class="computeroutput">completion_handler_for&lt;T, Signature&gt;</code>: Checks if
                <code class="computeroutput">T</code> is usable as a completion handler with the specified
                signature.
              </li>
<li class="listitem">
                <code class="computeroutput">completion_token_for&lt;T, Signature&gt;</code>: Checks if
                <code class="computeroutput">T</code> is a completion token that can be used with async_initiate
                and the specified signature.
              </li>
<li class="listitem">
                For backward compatibility with pre-concepts C++, the macros <code class="computeroutput">(BOOST_)ASIO_COMPLETION_SIGNATURE</code>,
                <code class="computeroutput">(BOOST_)ASIO_COMPLETION_HANDLER_FOR</code>, and <code class="computeroutput">(BOOST_)ASIO_COMPLETION_TOKEN_FOR</code>
                are provided. These macros expand to <code class="computeroutput">typename</code> when concepts
                are unsupported.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added the nested template type <code class="computeroutput">rebind_executor</code> to all I/O
          object types, as a way to generically rebind them to use alternative I/O
          executors. For example:
<pre class="programlisting">using my_socket_type = tcp::socket::rebind_executor&lt;my_executor_type&gt;::other;
</pre>
          <br>
        </li>
<li class="listitem">
          Changed the asynchronous operations' initiation function objects to report
          their associated I/O executor via the nested type <code class="computeroutput">executor_type</code>
          and member function <code class="computeroutput">get_executor()</code>. Note that the presence
          of <code class="computeroutput">executor_type</code> and <code class="computeroutput">get_executor()</code> should be
          treated as optional, and consequently it may be preferable to access them
          via the <code class="computeroutput">associated_executor</code> trait and the <code class="computeroutput">get_associated_executor()</code>
          helper function.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">default_completion_token</code> trait, so that every I/O
          executor type now has an associated default completion token type. This
          trait may be used in asynchronous operation declarations as follows:
<pre class="programlisting">template &lt;
    typename IoObject,
    typename CompletionToken =
      typename default_completion_token&lt;
        typename IoObject::executor_type
      &gt;::type
  &gt;
auto async_xyz(
    IoObject&amp; io_object,
    CompletionToken&amp;&amp; token =
      typename default_completion_token&lt;
        typename IoObject::executor_type
      &gt;::type{}
  );
</pre>
          <br> If not specialised, this trait type is <code class="computeroutput">void</code>, meaning
          no default completion token type is available for the given I/O executor.
        </li>
<li class="listitem">
          Specialised the <code class="computeroutput">default_completion_token</code> trait for the <code class="computeroutput">use_awaitable</code>
          completion token, so that it may be used as shown in the following example:
<pre class="programlisting">auto socket = use_awaitable.as_default_on(tcp::socket(my_context));
// ...
co_await socket.async_connect(my_endpoint); // Defaults to use_awaitable.
</pre>
          <br> In this example, the type of the <code class="computeroutput">socket</code> object is transformed
          from <code class="computeroutput">tcp::socket</code> to have an I/O executor with the default
          completion token set to <code class="computeroutput">use_awaitable</code>. Alternatively, the
          socket type may be computed directly:
<pre class="programlisting">using tcp_socket = use_awaitable_t&lt;&gt;::as_default_on_t&lt;tcp::socket&gt;;
tcp_socket socket(my_context);
// ...
co_await socket.async_connect(my_endpoint); // Defaults to use_awaitable.
</pre>
          <br>
        </li>
<li class="listitem">
          Added missing <code class="computeroutput">async_initiate</code> to the Windows-specific I/O objects'
          asynchronous operations.
        </li>
<li class="listitem">
          Ensured that the executor type is propagated to newly accepted sockets.
          When synchronously or asynchronously accepting a new connection, but without
          specifying an executor or execution context, the accept operation will
          now correctly propagate the executor type from the acceptor to the socket.
          For example, if your acceptor type is:
<pre class="programlisting">basic_socket_acceptor&lt;ip::tcp, my_executor_type&gt;
</pre>
          <br> then your accepted socket type will be:
<pre class="programlisting">basic_stream_socket&lt;ip::tcp, my_executor_type&gt;
</pre>
          <br>
        </li>
<li class="listitem">
          Changed to require that <code class="computeroutput">Protocol</code> copy and move operations
          never throw.
        </li>
<li class="listitem">
          Changed to require that <code class="computeroutput">Endpoint</code> default constructor and move
          operations never throw.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">noexcept</code> qualifier to protocol accessors.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">noexcept</code> qualifier to socket move constructors.
        </li>
<li class="listitem">
          Fixed issues associated with opening serial ports on Windows:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Use the correct constant to initialise the RTS control flag.
              </li>
<li class="listitem">
                Specify a default baud rate (9600).
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a lost "outstanding work count" that can occur when an
          asynchronous accept operation is automatically restarted.
        </li>
</ul></div>
<h4>
<a name="asio.history.h5"></a>
      <span><a name="asio.history.asio_1_14_1"></a></span><a class="link" href="history.html#asio.history.asio_1_14_1">Asio
      1.14.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved performance slightly by eliminating a redundant move construction
          when completed handlers are dispatched.
        </li>
<li class="listitem">
          Eliminated a compiler warning by annotating a <code class="computeroutput">case</code> fall-through
          in the free function <code class="computeroutput">connect()</code> implementation.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">is_*_buffer_sequence</code> detection traits for user-defined
          sequence types.
        </li>
<li class="listitem">
          Fixed some Windows-specific warnings about an incompatible pointer cast
          when obtaining the <code class="computeroutput">CancelIoEx</code> entry point.
        </li>
<li class="listitem">
          Changed to automatically set the defaults when opening a serial port on
          Windows.
        </li>
<li class="listitem">
          Changed the serial port <code class="computeroutput">get_option()</code> member function to be
          const.
        </li>
<li class="listitem">
          Fixed a name hiding issue with the WinRT stream-oriented socket backend's
          <code class="computeroutput">shutdown</code> function.
        </li>
<li class="listitem">
          Applied a minor fix to the documentation for <code class="computeroutput">is_dynamic_buffer</code>.
        </li>
<li class="listitem">
          Added some support for Haiku OS.
        </li>
<li class="listitem">
          Added wolfSSL compatability.
        </li>
<li class="listitem">
          Changed to require C++17 or later for coroutines TS support with clang.
        </li>
<li class="listitem">
          Fixed a doxygen generation problem in the tutorial.
        </li>
</ul></div>
<h4>
<a name="asio.history.h6"></a>
      <span><a name="asio.history.asio_1_14_0"></a></span><a class="link" href="history.html#asio.history.asio_1_14_0">Asio
      1.14.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved I/O object performance by adding runtime detection of native I/O
          executors when using the polymorphic executor wrapper.
        </li>
<li class="listitem">
          Changed I/O object move constructors so that the executor is copied, not
          moved. This ensures that the moved-from I/O object is left in the same
          state as if constructed with a valid executor but without a resource.
        </li>
<li class="listitem">
          On Windows, fixed an issue where global object destructors were not being
          run.
        </li>
<li class="listitem">
          Fixed move-based <code class="computeroutput">async_accept</code> between sockets with different
          executor types.
        </li>
</ul></div>
<h4>
<a name="asio.history.h7"></a>
      <span><a name="asio.history.asio_1_13_0"></a></span><a class="link" href="history.html#asio.history.asio_1_13_0">Asio
      1.13.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added custom I/O executor support to I/O objects.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                All I/O objects now have an additional <code class="computeroutput">Executor</code> template
                parameter. This template parameter defaults to the <code class="computeroutput">asio::executor</code>
                type (the polymorphic executor wrapper) but can be used to specify
                a user-defined executor type.
              </li>
<li class="listitem">
                I/O objects' constructors and functions that previously took an
                <code class="computeroutput">asio::io_context&amp;</code> now accept either an <code class="computeroutput">Executor</code>
                or a reference to a concrete <code class="computeroutput">ExecutionContext</code> (such
                as <code class="computeroutput">asio::io_context</code> or <code class="computeroutput">asio::thread_pool</code>).
              </li>
<li class="listitem">
                Note: One potential source of breakage in existing user code is when
                reusing an I/O object's <code class="computeroutput">io_context</code> for constructing
                another I/O object, as in:
<pre class="programlisting">asio::steady_timer my_timer(my_socket.get_executor().context());
</pre>
                <br> To fix this, either construct the second I/O object using
                the first I/O object's executor:<br>
<pre class="programlisting">asio::steady_timer my_timer(my_socket.get_executor());
</pre>
                <br> or otherwise explicitly pass the <code class="computeroutput">io_context</code>:<br>
<pre class="programlisting">asio::steady_timer my_timer(my_io_context);
</pre>
                <br>
              </li>
<li class="listitem">
                The previously deprecated <code class="computeroutput">get_io_context</code> and <code class="computeroutput">get_io_service</code>
                member functions have now been removed.
              </li>
<li class="listitem">
                The previously deprecated service template parameters, and the corresponding
                classes, have now been removed.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">async_result</code> form with an <code class="computeroutput">initiate</code>
          static member function.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                The <code class="computeroutput">async_result</code> template now supports a new form:
<pre class="programlisting">template &lt;typename CompletionToken, typename Signature&gt;
struct async_result
{
  typedef /* ... */ return_type;

  template &lt;typename Initiation,
      typename RawCompletionToken,
      typename... Args&gt;
  static return_type initiate(
      Initiation&amp;&amp; initiation,
      RawCompletionToken&amp;&amp; token,
      Args&amp;&amp;... args);
};
</pre>
                <br>
              </li>
<li class="listitem">
                The <code class="computeroutput">initiate</code> member function must: (a) transform the
                token into a completion handler object <code class="computeroutput">handler</code>; (b)
                cause the invocation of the function object <code class="computeroutput">initiation</code>
                as if by calling <code class="computeroutput">std::forward&lt;Initiation&gt;(initiation)(std::move(handler),
                std::forward&lt;Args&gt;(args)...)</code>. Note that the invocation
                of <code class="computeroutput">initiation</code> may be deferred (e.g. lazily evaluated),
                in which case <code class="computeroutput">initiation</code> and <code class="computeroutput">args</code> must
                be decay-copied and moved as required.
              </li>
<li class="listitem">
                A helper function template <code class="computeroutput">async_initiate</code> has also been
                added as a wrapper for the invocation of <code class="computeroutput">async_result&lt;&gt;::initiate</code>.
                For backward compatibility, this function supports both the old and
                new <code class="computeroutput">async_result</code> forms.
              </li>
<li class="listitem">
                The composed operations examples have been updated to use <code class="computeroutput">async_initiate</code>.
              </li>
<li class="listitem">
                The previously deprecated <code class="computeroutput">handler_type</code> trait and single-argument
                form of <code class="computeroutput">async_result</code> have now been removed.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Updated the Coroutines TS support and promoted it to the <code class="computeroutput">asio</code>
          namespace.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                The <code class="computeroutput">awaitable&lt;&gt;</code>, <code class="computeroutput">co_spawn</code>, <code class="computeroutput">this_coro</code>,
                <code class="computeroutput">detached</code>, and <code class="computeroutput">redirect_error</code> facilities
                have been moved from the <code class="computeroutput">asio::experimental</code> namespace
                to namespace <code class="computeroutput">asio</code>. As part of this change, the <code class="computeroutput">this_coro::token()</code>
                awaitable has been superseded by the <code class="computeroutput">asio::use_awaitable</code>
                completion token.
              </li>
<li class="listitem">
                Please note that the <code class="computeroutput">use_awaitable</code> and <code class="computeroutput">redirect_error</code>
                completion tokens work only with asynchronous operations that use
                the new form of <code class="computeroutput">async_result</code> with member function <code class="computeroutput">initiate</code>.
                Furthermore, when using <code class="computeroutput">use_awaitable</code>, please be aware
                that the asynchronous operation is not initiated until <code class="computeroutput">co_await</code>
                is applied to the <code class="computeroutput">awaitable&lt;&gt;</code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">DynamicBuffer_v2</code> concept which is CopyConstructible.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                This change adds a new set of type requirements for dynamic buffers,
                <code class="computeroutput">DynamicBuffer_v2</code>, which supports copy construction.
                These new type requirements enable dynamic buffers to be used as
                arguments to user-defined composed operations, where the same dynamic
                buffer object is used repeatedly for multiple underlying operations.
                For example:<br>
<pre class="programlisting">template &lt;typename DynamicBuffer&gt;
void echo_line(tcp::socket&amp; sock, DynamicBuffer buf)
{
  n = asio::read_until(sock, buf, '\n');
  asio::write(sock, buf, asio::transfer_exactly(n));
}
</pre>
                <br>
              </li>
<li class="listitem">
                The original <code class="computeroutput">DynamicBuffer</code> type requirements have been
                renamed to <code class="computeroutput">DynamicBuffer_v1</code>. These requirements continue
                to be compatible with the Networking TS.
              </li>
<li class="listitem">
                New type traits <code class="computeroutput">is_dynamic_buffer_v1</code> and <code class="computeroutput">is_dynamic_buffer_v2</code>
                have been added to test for conformance to <code class="computeroutput">DynamicBuffer_v1</code>
                and <code class="computeroutput">DynamicBuffer_v2</code> respectively. The existing <code class="computeroutput">is_dynamic_buffer</code>
                trait has been retained and delegates to <code class="computeroutput">is_dynamic_buffer_v1</code>
                (unless <code class="computeroutput">ASIO_NO_DYNAMIC_BUFFER_V1</code> is explicitly defined,
                in which case it delegates to <code class="computeroutput">is_dynamic_buffer_v2</code>).
              </li>
<li class="listitem">
                For convenience, the <code class="computeroutput">dynamic_string_buffer</code> and <code class="computeroutput">dynamic_vector_buffer</code>
                classes conform to both <code class="computeroutput">DynamicBuffer_v1</code> and <code class="computeroutput">DynamicBuffer_v2</code>
                requirements.
              </li>
<li class="listitem">
                When <code class="computeroutput">ASIO_NO_DYNAMIC_BUFFER_V1</code> is defined, all support
                for <code class="computeroutput">DynamicBuffer_v1</code> types and functions is #ifdef-ed
                out. Support for using <code class="computeroutput">basic_streambuf</code> with the <code class="computeroutput">read</code>,
                <code class="computeroutput">async_read</code>, <code class="computeroutput">read_until</code>, <code class="computeroutput">async_read_until</code>,
                <code class="computeroutput">write</code>, and <code class="computeroutput">async_write</code> functions is also
                disabled as a consequence.
              </li>
<li class="listitem">
                Note: This change should have no impact on existing source code that
                simply uses dynamic buffers in conjunction with Asio's composed operations.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">async_compose</code> function that simplifies the implementation
          of user-defined asynchronous operations.
        </li>
<li class="listitem">
          Added a <code class="computeroutput">make_strand</code> function, which creates a <code class="computeroutput">strand</code>
          with a deduced <code class="computeroutput">Executor</code> template argument.
        </li>
<li class="listitem">
          Relaxed the completion condition type requirements to only require move-constructibility
          rather than copy-constructibility.
        </li>
<li class="listitem">
          Added a constructor for <code class="computeroutput">local::basic_endpoint</code> that takes a
          <code class="computeroutput">string_view</code>.
        </li>
<li class="listitem">
          Added the noexcept qualifier to various member functions of the <code class="computeroutput">ip::address</code>,
          <code class="computeroutput">ip::address_v4</code>, <code class="computeroutput">ip::address_v6</code>, <code class="computeroutput">ip::basic_endpoint</code>,
          and <code class="computeroutput">executor_work_guard</code> classes.
        </li>
<li class="listitem">
          Added the noexcept qualifier to the <code class="computeroutput">buffer_sequence_begin</code>
          and <code class="computeroutput">buffer_sequence_end</code> functions.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">ASIO_DISABLE_VISIBILITY</code> configuration <code class="computeroutput">#define</code>
          that allows visibility pragmas to be disabled. (Note: If symbols are hidden,
          extra care must be taken to ensure that Asio types are not passed across
          shared library API boundaries.)
        </li>
<li class="listitem">
          Changed compile-time feature detection to define <code class="computeroutput">ASIO_STANDALONE</code>
          automatically if C++11 or later is detected.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Users should define <code class="computeroutput">ASIO_ENABLE_BOOST</code> to explicitly
                disable standalone mode when compiling with C++11 or later.
              </li>
<li class="listitem">
                The <code class="computeroutput">configure</code> script now defaults to a standalone build
                unless Boost is specified or detected.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Enabled recycling of the memory used to type-erase a function object with
          the polymorphic executor.
        </li>
<li class="listitem">
          Changed receive operations to return the correct number of bytes transferred
          when truncation (<code class="computeroutput">error::message_size</code>) occurs on a datagram-oriented
          socket.
        </li>
<li class="listitem">
          Fixed multicast behaviour on QNX by automatically applying <code class="computeroutput">SO_REUSEPORT</code>
          when the <code class="computeroutput">reuse_address</code> option is set.
        </li>
<li class="listitem">
          Added inclusion of <code class="computeroutput">unistd.h</code> when targeting Haiku OS, to fix
          feature detection.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">network_v[46].hpp</code> headers to the top-level convenience
          header.
        </li>
<li class="listitem">
          Fixed calculation of absolute timeout when the backend uses <code class="computeroutput">pthread_cond_timedwait</code>.
        </li>
<li class="listitem">
          Changed the range-based asynchronous connect operation to deduce the <code class="computeroutput">EndpointSequence</code>
          iterator type rather than assume the presence of a <code class="computeroutput">const_iterator</code>
          typedef.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">buffer_sequence_begin</code> and <code class="computeroutput">buffer_sequence_end</code>
          to prevent implicit conversion. This change addresses an issue where a
          call to <code class="computeroutput">buffer_sequence_begin</code> or <code class="computeroutput">buffer_sequence_end</code>
          could trigger an implicit conversion to <code class="computeroutput">const_buffer</code> or <code class="computeroutput">mutable_buffer</code>.
          Whenever this implicit conversion occurred, the return value of <code class="computeroutput">buffer_sequence_begin</code>
          or <code class="computeroutput">buffer_sequence_end</code> would point to a temporary object.
        </li>
<li class="listitem">
          Ensured SSL handshake errors are propagated to the peer before the local
          operation completes.
        </li>
<li class="listitem">
          Suppressed the <code class="computeroutput">eof</code> error on SSL shutdown as it actually indicates
          success.
        </li>
<li class="listitem">
          Added a fallback error code for when we OpenSSL produces an <code class="computeroutput">SSL_ERROR_SYSCALL</code>
          result without an associated error.
        </li>
<li class="listitem">
          Changed composed asynchronous read and write operations to move, rather
          than copy, the buffer sequence objects when the composed operation implementation
          is moved.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">&lt;atomic&gt;</code> when targeting apple/clang/libc++
          with recent Xcode versions, even for C++03. This fixes a warning about
          the deprecation of <code class="computeroutput">OSMemoryBarrier</code>.
        </li>
<li class="listitem">
          Fixed compile errors that occur when using the composed read and write
          operations with MSVC 11.0, by disabling <code class="computeroutput">decltype</code> support for
          that compiler.
        </li>
<li class="listitem">
          Increased the default value of <code class="computeroutput">_WIN32_WINNT</code> to <code class="computeroutput">0x0601</code>
          (Windows 7).
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">dispatch</code> documentation to note that it may call the
          supplied function object in the current thread.
        </li>
<li class="listitem">
          Updated <code class="computeroutput">post</code> and <code class="computeroutput">defer</code> documentation to clarify
          the the distinction between them.
        </li>
</ul></div>
<h4>
<a name="asio.history.h8"></a>
      <span><a name="asio.history.asio_1_12_2"></a></span><a class="link" href="history.html#asio.history.asio_1_12_2">Asio
      1.12.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed a problem with the detection of <code class="computeroutput">std::future</code> availability
          with libstdc++.
        </li>
<li class="listitem">
          Fixed compile error in regex overload of <code class="computeroutput">read_until</code>.
        </li>
<li class="listitem">
          Fixed a timer heap corruption issue that can occur when moving a cancelled
          timer.
        </li>
<li class="listitem">
          Fixed detection of <code class="computeroutput">std::experimental::string_view</code> and <code class="computeroutput">std::string_view</code>
          with newer clang/libc++.
        </li>
<li class="listitem">
          Fixed MSVC version detection for availability of <code class="computeroutput">std::invoke_result</code>.
        </li>
<li class="listitem">
          Fixed the buffer sequence traits to test the new requirements, if <code class="computeroutput">decltype</code>
          is available.
        </li>
<li class="listitem">
          Fixed an MSVC issue when building with exceptions disabled.
        </li>
<li class="listitem">
          Added SSL context options for TLS v1.3.
        </li>
<li class="listitem">
          Added a compile-time test for TLS v1 support.
        </li>
<li class="listitem">
          Fixed the macro used to test for TLS v1.2 support.
        </li>
<li class="listitem">
          Prevented global objects from being created once per thread on Windows.
        </li>
<li class="listitem">
          Fixed a crash when using <code class="computeroutput">size()</code>, <code class="computeroutput">max_size()</code> or
          <code class="computeroutput">empty()</code> on default-constructed resolver results.
        </li>
<li class="listitem">
          Changed to move the return value in basic_resolver_results::begin() to
          avoid copying.
        </li>
<li class="listitem">
          Enabled move support for the Intel Compiler.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">std::string_view</code> detection issue when using clang-cl.
        </li>
<li class="listitem">
          Fixed the handler tracking operation name for <code class="computeroutput">io_context::executor_type::dispatch</code>.
        </li>
<li class="listitem">
          Fixed a buffer overflow that could occur when parsing an address string
          with a 64-bit scope id.
        </li>
<li class="listitem">
          Added examples showing how to write composed operations.
        </li>
<li class="listitem">
          Added C++11 versions of the Timeouts, Timers, SOCKS4 and SSL examples.
        </li>
<li class="listitem">
          Fixed minor issues in documentation and examples.
        </li>
</ul></div>
<h4>
<a name="asio.history.h9"></a>
      <span><a name="asio.history.asio_1_12_1"></a></span><a class="link" href="history.html#asio.history.asio_1_12_1">Asio
      1.12.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added missing const qualifier to <code class="computeroutput">basic_socket_acceptor::get_option</code>.
        </li>
<li class="listitem">
          Worked around a parsing error that occurs with some versions of gcc.
        </li>
<li class="listitem">
          Fixed broken code samples in tutorial.
        </li>
<li class="listitem">
          Added new experimental features. (Note that "experimental" features
          may be changed without notice in subsequent releases.)
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Added <code class="computeroutput">experimental::detached</code> completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput">experimental::redirect_error</code> completion token.
              </li>
<li class="listitem">
                Added <code class="computeroutput">experimental::co_spawn</code> facility for integration
                with the coroutines technical specification.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Updated timeout examples to use latest features.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Used <code class="computeroutput">asio::steady_timer</code> rather than <code class="computeroutput">asio::deadline_timer</code>.
              </li>
<li class="listitem">
                Used <code class="computeroutput">asio::dynamic_buffer</code> rather than <code class="computeroutput">asio::streambuf</code>.
              </li>
<li class="listitem">
                Used timed <code class="computeroutput">asio::io_context::run_for()</code> function for
                blocking clients.
              </li>
<li class="listitem">
                Added example showing a custom completion token for blocking with
                timeouts.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed unit tests to compile when <code class="computeroutput">(BOOST_)ASIO_NO_DEPRECATED</code>
          is defined.
        </li>
<li class="listitem">
          Changed socket iostreams to use chrono by default, to fix compatibility
          with the Networking TS. Define <code class="computeroutput">(BOOST_)ASIO_USE_BOOST_DATE_TIME_FOR_SOCKET_IOSTREAM</code>
          to enable the old Boost.Date_Time interface in <code class="computeroutput">basic_socket_streambuf</code>
          and <code class="computeroutput">basic_socket_iostream</code>.
        </li>
<li class="listitem">
          Updated examples to use chrono rather than Boost.Date_Time.
        </li>
<li class="listitem">
          Fixed an incorrect member function detector in the <code class="computeroutput">is_dynamic_buffer</code>
          trait.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput">async_result</code> incompatibility with deprecated <code class="computeroutput">handler_type</code>.
        </li>
<li class="listitem">
          Added a missing move optimisation in the SSL stream implementation.
        </li>
<li class="listitem">
          Fixed incorrect <code class="computeroutput">basic_resolver_results::value_type</code> typedef.
        </li>
<li class="listitem">
          Fixed a compile error with some OpenSSL versions when <code class="computeroutput">SSL_OP_NO_COMPRESSION</code>
          is defined.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">add_certificate_authority</code> to process multiple certificates
          in a bundle.
        </li>
<li class="listitem">
          Eliminated deprecation warning with MSVC by using <code class="computeroutput">std::invoke_result</code>
          rather than <code class="computeroutput">std::result_of</code>.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">std::string_view</code> for C++17 or later, and <code class="computeroutput">std::experimental::string_view</code>
          for C++14. Define the preprocessor macro <code class="computeroutput">(BOOST_)ASIO_DISABLE_STD_STRING_VIEW</code>
          to force the use of std::experimental::string_view (assuming it is available)
          when compiling in C++17 mode.
        </li>
<li class="listitem">
          Ensured <code class="computeroutput">DynamicBuffer</code> template arguments are decayed before
          using in <code class="computeroutput">enable_if</code> tests.
        </li>
<li class="listitem">
          Changed documentation to distinguish legacy completion handlers (which
          are still required to be CopyConstructible) from new MoveConstructible
          handlers.
        </li>
<li class="listitem">
          Suppressed a discarded return value warning in the buffer debugging support.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">basic_yield_context</code> to work with completion signatures
          containing reference parameters.
        </li>
<li class="listitem">
          Ensured that stackful coroutines launched using <code class="computeroutput">spawn()</code> correctly
          store decayed copies of their function and handler arguments.
        </li>
<li class="listitem">
          Fixed some compatibility issues with Android.
        </li>
<li class="listitem">
          Fixed some minor portability issues in examples.
        </li>
</ul></div>
<h4>
<a name="asio.history.h10"></a>
      <span><a name="asio.history.asio_1_12_0"></a></span><a class="link" href="history.html#asio.history.asio_1_12_0">Asio
      1.12.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Completed the interface changes to reflect the Networking TS (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4656.pdf" target="_top">N4656</a>).
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                See the <a class="link" href="net_ts.html" title="Networking TS compatibility">list</a> of new interfaces
                and, where applicable, the corresponding old interfaces that have
                been superseded.
              </li>
<li class="listitem">
                The service template parameters, and the corresponding classes, are
                disabled by default. For example, instead of <code class="computeroutput">basic_socket&lt;Protocol,
                SocketService&gt;</code> we now have simply <code class="computeroutput">basic_socket&lt;Protocol&gt;</code>.
                The old interface can be enabled by defining the <code class="computeroutput">(BOOST_)ASIO_ENABLE_OLD_SERVICES</code>
                macro.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added support for customised handler tracking.
        </li>
<li class="listitem">
          Added reactor-related (i.e. descriptor readiness) events to handler tracking.
        </li>
<li class="listitem">
          Added special <a class="link" href="overview/core/concurrency_hint.html" title="Concurrency Hints">concurrency
          hint</a> values that may be used to disable locking on a per <code class="computeroutput">io_context</code>
          basis.
        </li>
<li class="listitem">
          Enabled perfect forwarding for the first <code class="computeroutput">ssl::stream&lt;&gt;</code>
          constructor argument.
        </li>
<li class="listitem">
          Added ability to release ownership of the underlying native socket. (Requires
          Windows 8.1 or later when using the I/O completion port backend.)
        </li>
</ul></div>
<h4>
<a name="asio.history.h11"></a>
      <span><a name="asio.history.asio_1_11_0"></a></span><a class="link" href="history.html#asio.history.asio_1_11_0">Asio
      1.11.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented changes to substantially reflect the Networking Library Proposal
          (<a href="../www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/n4370.html" target="_top">N4370</a>).
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                New <code class="computeroutput">Executor</code> type requirements and classes to support
                an executor framework, including the <code class="computeroutput">execution_context</code>
                base class, the <code class="computeroutput">executor_work</code> class for tracking outstanding
                work, and the <code class="computeroutput">executor</code> polymorphic wrapper. Free functions
                <code class="computeroutput">dispatch()</code>, <code class="computeroutput">post()</code> and <code class="computeroutput">defer()</code>
                have been added and are used to submit function objects to executors.
              </li>
<li class="listitem">
                Completion handlers now have an associated executor and associated
                allocator. The free function <code class="computeroutput">wrap()</code> is used to associate
                an executor with a handler or other object. The handler hooks for
                allocation, invocation and continuation have been deprecated.
              </li>
<li class="listitem">
                A <code class="computeroutput">system_executor</code> class has been added as a default
                executor.
              </li>
<li class="listitem">
                The <code class="computeroutput">io_service</code> class is now derived from <code class="computeroutput">execution_context</code>
                and implements the executor type requirements in its nested <code class="computeroutput">executor_type</code>
                class. The member functions <code class="computeroutput">dispatch()</code>, <code class="computeroutput">post()</code>,
                <code class="computeroutput">defer()</code> and <code class="computeroutput">wrap()</code> have been deprecated.
                The <code class="computeroutput">io_service::work</code> class has been deprecated.
              </li>
<li class="listitem">
                The <code class="computeroutput">io_service</code> member function <code class="computeroutput">reset()</code>
                has been renamed to <code class="computeroutput">restart()</code>. The old name is retained
                for backward compatibility but has been deprecated.
              </li>
<li class="listitem">
                The <code class="computeroutput">make_service&lt;&gt;()</code> function is now used to add
                a new service to an execution context such as an <code class="computeroutput">io_service</code>.
                The <code class="computeroutput">add_service()</code> function has been deprecated.
              </li>
<li class="listitem">
                A new <code class="computeroutput">strand&lt;&gt;</code> template has been added to allow
                strand functionality to be used with generic executor types.
              </li>
<li class="listitem">
                I/O objects (such as sockets and timers) now provide access to their
                associated <code class="computeroutput">io_service</code> via a <code class="computeroutput">context()</code> member
                function. The <code class="computeroutput">get_io_service()</code> member function is deprecated.
              </li>
<li class="listitem">
                All asynchronous operations and executor operations now support move-only
                handlers. However, the deprecated <code class="computeroutput">io_service::post()</code>,
                <code class="computeroutput">io_service::dispatch()</code>, <code class="computeroutput">io_service::strand::post()</code>
                and <code class="computeroutput">io_service::strand::dispatch()</code> functions still require
                copyable handlers.
              </li>
<li class="listitem">
                Waitable timer objects are now movable.
              </li>
<li class="listitem">
                Waitable timers, socket iostreams and socket streambufs now provide
                an <code class="computeroutput">expiry()</code> member function for obtaining the expiry
                time. The accessors <code class="computeroutput">expires_at()</code> and <code class="computeroutput">expires_after()</code>
                have been deprecated, though those names are retained for the mutating
                members.
              </li>
<li class="listitem">
                The <code class="computeroutput">std::packaged_task</code> class template is now supported
                as a completion handler. The initiating operation automatically returns
                the future associated with the task. The <code class="computeroutput">package()</code> function
                has been added as a convenient factory for packaged tasks.
              </li>
<li class="listitem">
                Sockets, socket acceptors and descriptors now provide <code class="computeroutput">wait()</code>
                and <code class="computeroutput">async_wait()</code> operations that may be used to wait
                for readiness. The <code class="computeroutput">null_buffers</code> type has been deprecated.
              </li>
<li class="listitem">
                The proposed error code enum classes are simulated using namespaces.
                Existing asio error codes now have a correspondence with the standard
                error conditions.
              </li>
<li class="listitem">
                Conversion between IP address types, and conversion from string to
                address, is now supported via the <code class="computeroutput">address_cast&lt;&gt;()</code>,
                <code class="computeroutput">make_address()</code>, <code class="computeroutput">make_address_v4()</code> and
                <code class="computeroutput">make_address_v6()</code> free functions. The <code class="computeroutput">from_string()</code>,
                <code class="computeroutput">to_v4()</code>, <code class="computeroutput">to_v6()</code> and <code class="computeroutput">v4_mapped()</code>
                member functions have been deprecated.
              </li>
<li class="listitem">
                A default-constructed <code class="computeroutput">ip::address</code> now represents an
                invalid address value that is neither IPv4 nor IPv6.
              </li>
<li class="listitem">
                New <code class="computeroutput">buffer()</code> overloads that generate mutable buffers
                for non-const <code class="computeroutput">string</code> objects.
              </li>
<li class="listitem">
                Support for dynamic buffer sequences that automatically grow and
                shrink to accomodate data as it is read or written. This is a generic
                facility similar to the existing <code class="computeroutput">asio::streambuf</code> class.
                This support includes:
                <div class="itemizedlist"><ul class="itemizedlist" type="square">
<li class="listitem">
                      New <code class="computeroutput">dynamic_string_buffer</code> and <code class="computeroutput">dynamic_vector_buffer</code>
                      adapter classes that meet the <code class="computeroutput">DynamicBufferSequence</code>
                      type requirements.
                    </li>
<li class="listitem">
                      New <code class="computeroutput">dynamic_buffer()</code> factory functions for creating
                      a dynamic buffer adapter for a <code class="computeroutput">vector</code> or <code class="computeroutput">string</code>.
                    </li>
<li class="listitem">
                      New overloads for the <code class="computeroutput">read()</code>, <code class="computeroutput">async_read()</code>,
                      <code class="computeroutput">write()</code> and <code class="computeroutput">async_write()</code>, <code class="computeroutput">read_until()</code>
                      and <code class="computeroutput">async_read_until()</code> free functions that directly
                      support dynamic buffer sequences.
                    </li>
</ul></div>
              </li>
<li class="listitem">
                Support for networks and address ranges. Thanks go to Oliver Kowalke
                for contributing to the design and providing the implementation on
                which this facility is based. The following new classes have been
                added:
                <div class="itemizedlist"><ul class="itemizedlist" type="square">
<li class="listitem">
                      <code class="computeroutput">address_iterator_v4</code> for iterating across IPv4
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_iterator_v6</code> for iterating across IPv6
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_range_v4</code> to represent a range of IPv4
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">address_range_v6</code> to represent a range of IPv6
                      addresses
                    </li>
<li class="listitem">
                      <code class="computeroutput">network_v4</code> for manipulating IPv4 CIDR addresses,
                      e.g. 1.2.3.0/24
                    </li>
<li class="listitem">
                      <code class="computeroutput">network_v6</code> for manipulating IPv6 CIDR addresses,
                      e.g. ffe0:/120
                    </li>
</ul></div>
              </li>
<li class="listitem">
                New convenience headers in <code class="literal">&lt;asio/ts/*.hpp&gt;</code>
                that correspond to the headers in the proposal.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Added a new, executor-aware <code class="computeroutput">thread_pool</code> class.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">spawn()</code> to be executor-aware.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">spawn()</code> overload that takes only a function object.
        </li>
<li class="listitem">
          Changed <code class="computeroutput">spawn()</code> and <code class="computeroutput">yield_context</code> to permit nested
          calls to the completion handler.
        </li>
<li class="listitem">
          Removed previously deprecated functions.
        </li>
<li class="listitem">
          Added options for disabling TLS v1.1 and v1.2.
        </li>
<li class="listitem">
          Changed the SSL wrapper to call the password callback when loading an in-memory
          key.
        </li>
<li class="listitem">
          Changed the tutorial to use <code class="computeroutput">std::endl</code> to ensure output is
          flushed.
        </li>
<li class="listitem">
          Fixed false SSL error reports by ensuring that the SSL error queue is cleared
          prior to each operation.
        </li>
<li class="listitem">
          Fixed an <code class="computeroutput">ssl::stream&lt;&gt;</code> bug that may result in spurious
          'short read' errors.
        </li>
<li class="listitem">
          Enabled perfect forwarding for the first <code class="computeroutput">ssl::stream&lt;&gt;</code>
          constructor argument.
        </li>
<li class="listitem">
          Added standalone Asio support for Clang when used with libstdc++ and C++11.
        </li>
<li class="listitem">
          Fixed an unsigned integer overflow reported by Clang's integer sanitizer.
        </li>
<li class="listitem">
          Added support for move-only return types when using a <code class="computeroutput">yield_context</code>
          object with asynchronous operations.
        </li>
<li class="listitem">
          Ensured errors generated by Windows' <code class="computeroutput">ConnectEx</code> function are
          mapped to their portable equivalents.
        </li>
<li class="listitem">
          Changed multicast test to treat certain <code class="computeroutput">join_group</code> failures
          as non-fatal.
        </li>
</ul></div>
<h4>
<a name="asio.history.h12"></a>
      <span><a name="asio.history.asio_1_10_5"></a></span><a class="link" href="history.html#asio.history.asio_1_10_5">Asio
      1.10.5</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed the <code class="literal">kqueue</code> reactor so that it works on FreeBSD.
        </li>
<li class="listitem">
          Fixed an issue in the <code class="literal">kqueue</code> reactor which resulted
          in spinning when using serial ports on Mac OS.
        </li>
<li class="listitem">
          Fixed <code class="literal">kqueue</code> reactor support for read-only file descriptors.
        </li>
<li class="listitem">
          Fixed a compile error when using the <code class="literal">/dev/poll</code> reactor.
        </li>
<li class="listitem">
          Changed the Windows backend to use <code class="computeroutput">WSASocketW</code>, as <code class="computeroutput">WSASocketA</code>
          has been deprecated.
        </li>
<li class="listitem">
          Fixed some warnings reported by Visual C++ 2013.
        </li>
<li class="listitem">
          Fixed integer type used in the WinRT version of the byte-order conversion
          functions.
        </li>
<li class="listitem">
          Changed documentation to indicate that <code class="computeroutput">use_future</code> and <code class="computeroutput">spawn()</code>
          are not made available when including the <code class="computeroutput">asio.hpp</code> convenience
          header.
        </li>
<li class="listitem">
          Explicitly marked <code class="computeroutput">asio::strand</code> as deprecated. Use <code class="computeroutput">asio::io_service::strand</code>
          instead.
        </li>
</ul></div>
<h4>
<a name="asio.history.h13"></a>
      <span><a name="asio.history.asio_1_10_4"></a></span><a class="link" href="history.html#asio.history.asio_1_10_4">Asio
      1.10.4</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Stopped using certain Winsock functions that are marked as deprecated in
          the latest Visual C++ and Windows SDK.
        </li>
<li class="listitem">
          Fixed a shadow variable warning on Windows.
        </li>
<li class="listitem">
          Fixed a regression in the <code class="literal">kqueue</code> backend that was introduced
          in Asio 1.10.2.
        </li>
<li class="listitem">
          Added a workaround for building the unit tests with <code class="literal">gcc</code>
          on AIX.
        </li>
</ul></div>
<h4>
<a name="asio.history.h14"></a>
      <span><a name="asio.history.asio_1_10_3"></a></span><a class="link" href="history.html#asio.history.asio_1_10_3">Asio
      1.10.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Worked around a <code class="literal">gcc</code> problem to do with anonymous enums.
        </li>
<li class="listitem">
          Reverted the Windows <code class="computeroutput">HANDLE</code> backend change to ignore <code class="computeroutput">ERROR_MORE_DATA</code>.
          Instead, the error will be propagated as with any other (i.e. in an <code class="computeroutput">error_code</code>
          or thrown as a <code class="computeroutput">system_error</code>), and the number of bytes transferred
          will be returned. For code that needs to handle partial messages, the
          <code class="computeroutput">error_code</code> overload should be used.
        </li>
<li class="listitem">
          Fixed an off-by-one error in the <code class="computeroutput">signal_set</code> implementation's
          signal number check.
        </li>
<li class="listitem">
          Changed the Windows IOCP backend to not assume that <code class="computeroutput">SO_UPDATE_CONNECT_CONTEXT</code>
          is defined.
        </li>
<li class="listitem">
          Fixed a Windows-specific issue, introduced in Asio 1.10.2, by using <code class="computeroutput">VerifyVersionInfo</code>
          rather than <code class="computeroutput">GetVersionEx</code>, as <code class="computeroutput">GetVersionEx</code> has
          been deprecated.
        </li>
<li class="listitem">
          Changed to use SSE2 intrinsics rather than inline assembly, to allow the
          Cray compiler to work.
        </li>
</ul></div>
<h4>
<a name="asio.history.h15"></a>
      <span><a name="asio.history.asio_1_10_2"></a></span><a class="link" href="history.html#asio.history.asio_1_10_2">Asio
      1.10.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed <code class="computeroutput">asio::spawn()</code> to work correctly with new Boost.Coroutine
          interface.
        </li>
<li class="listitem">
          Ensured that incomplete <code class="computeroutput">asio::spawn()</code> coroutines are correctly
          unwound when cleaned up by the <code class="computeroutput">io_service</code> destructor.
        </li>
<li class="listitem">
          Fixed delegation of continuation hook for handlers produced by <code class="computeroutput">io_service::wrap()</code>
          and <code class="computeroutput">strand::wrap()</code>.
        </li>
<li class="listitem">
          Changed the Windows I/O completion port backend to use <code class="computeroutput">ConnectEx</code>,
          if available, for connection-oriented IP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">io_service</code> backend for non-Windows (and non-IOCP
          Windows) platforms to use a single condition variable per <code class="computeroutput">io_service</code>
          instance. This addresses a potential race condition when <code class="computeroutput">run_one()</code>
          is used from multiple threads.
        </li>
<li class="listitem">
          Prevented integer overflow when computing timeouts based on some <code class="computeroutput">boost::chrono</code>
          and <code class="computeroutput">std::chrono</code> clocks.
        </li>
<li class="listitem">
          Made further changes to <code class="computeroutput">EV_CLEAR</code> handling in the kqueue backend,
          to address other cases where the <code class="computeroutput">close()</code> system call may hang
          on Mac OS X.
        </li>
<li class="listitem">
          Fixed infinite recursion in implementation of <code class="computeroutput">resolver_query_base::flags::operator~</code>.
        </li>
<li class="listitem">
          Made the <code class="computeroutput">select</code> reactor more efficient on Windows for large
          numbers of sockets.
        </li>
<li class="listitem">
          Fixed a Windows-specific type-aliasing issue reported by <code class="literal">gcc</code>.
        </li>
<li class="listitem">
          Prevented execution of compile-time-only buffer test to avoid triggering
          an address sanitiser warning.
        </li>
<li class="listitem">
          Disabled the <code class="computeroutput">GetQueuedCompletionStatus</code> timeout workaround
          on recent versions of Windows.
        </li>
<li class="listitem">
          Changed implementation for Windows Runtime to use <code class="computeroutput">FormatMessageW</code>
          rather than <code class="computeroutput">FormatMessageA</code>, as the Windows store does not
          permit the latter.
        </li>
<li class="listitem">
          Added support for string-based scope IDs when using link-local multicast
          addresses.
        </li>
<li class="listitem">
          Changed IPv6 multicast group join to use the address's scope ID as the
          interface, if an interface is not explicitly specified.
        </li>
<li class="listitem">
          Fixed multicast test failure on Mac OS X and the BSDs by using a link-local
          multicast address.
        </li>
<li class="listitem">
          Various minor documentation improvements.
        </li>
</ul></div>
<h4>
<a name="asio.history.h16"></a>
      <span><a name="asio.history.asio_1_10_1"></a></span><a class="link" href="history.html#asio.history.asio_1_10_1">Asio
      1.10.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented a limited port to Windows Runtime. This support requires that
          the language extensions be enabled. Due to the restricted facilities exposed
          by the Windows Runtime API, the port also comes with the following caveats:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                The core facilities such as the <code class="computeroutput">io_service</code>, <code class="computeroutput">strand</code>,
                buffers, composed operations, timers, etc., should all work as normal.
              </li>
<li class="listitem">
                For sockets, only client-side TCP is supported.
              </li>
<li class="listitem">
                Explicit binding of a client-side TCP socket is not supported.
              </li>
<li class="listitem">
                The <code class="computeroutput">cancel()</code> function is not supported for sockets.
                Asynchronous operations may only be cancelled by closing the socket.
              </li>
<li class="listitem">
                Operations that use <code class="computeroutput">null_buffers</code> are not supported.
              </li>
<li class="listitem">
                Only <code class="computeroutput">tcp::no_delay</code> and <code class="computeroutput">socket_base::keep_alive</code>
                options are supported.
              </li>
<li class="listitem">
                Resolvers do not support service names, only numbers. I.e. you must
                use "80" rather than "http".
              </li>
<li class="listitem">
                Most resolver query flags have no effect.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Extended the ability to use Asio without Boost to include Microsoft Visual
          Studio 2012. When using a C++11 compiler, most of Asio may now be used
          without a dependency on Boost header files or libraries. To use Asio in
          this way, define <code class="computeroutput">ASIO_STANDALONE</code> on your compiler command
          line or as part of the project options. This standalone configuration has
          been tested for the following platforms and compilers:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Microsoft Visual Studio 2012
              </li>
<li class="listitem">
                Linux with g++ 4.7 or 4.8 (requires <code class="literal">-std=c++11</code>)
              </li>
<li class="listitem">
                Mac OS X with clang++ / Xcode 4.6 (requires <code class="literal">-std=c++11 -stdlib=libc++</code>)
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a regression (introduced in 1.10.0) where, on some platforms, errors
          from <code class="computeroutput">async_connect</code> were not correctly propagated through to
          the completion handler.
        </li>
<li class="listitem">
          Fixed a Windows-specific regression (introduced in 1.10.0) that occurs
          when multiple threads are running an <code class="computeroutput">io_service</code>. When the
          bug occurs, the result of an asynchronous operation (error and bytes tranferred)
          is incorrectly discarded and zero values used instead. For TCP sockets
          this results in spurious end-of-file notifications.
        </li>
<li class="listitem">
          Fixed a bug in handler tracking, where it was not correctly printing out
          some handler IDs.
        </li>
<li class="listitem">
          Fixed the comparison used to test for successful synchronous accept operations
          so that it works correctly with unsigned socket descriptors.
        </li>
<li class="listitem">
          Ensured the signal number is correctly passed to the completion handler
          when starting an <code class="computeroutput">async_wait</code> on a signal that is already raised.
        </li>
<li class="listitem">
          Suppressed a g++ 4.8+ warning about unused typedefs.
        </li>
<li class="listitem">
          Enabled the move optimisation for handlers that use the default invocation
          hook.
        </li>
<li class="listitem">
          Clarified that programs must not issue overlapping <code class="computeroutput">async_write_at</code>
          operations.
        </li>
<li class="listitem">
          Changed the Windows <code class="computeroutput">HANDLE</code> backend to treat <code class="computeroutput">ERROR_MORE_DATA</code>
          as a non-fatal error when returned by <code class="computeroutput">GetOverlappedResult</code>
          for a synchronous read.
        </li>
<li class="listitem">
          Visual C++ language extensions use <code class="computeroutput">generic</code> as a keyword. Added
          a workaround that renames the namespace to <code class="computeroutput">cpp_generic</code> when
          those language extensions are in effect.
        </li>
<li class="listitem">
          Fixed some asynchronous operations that missed out on getting <code class="computeroutput">async_result</code>
          support in 1.10.0. In particular, the buffered stream templates have been
          updated so that they adhere to current handler patterns.
        </li>
<li class="listitem">
          Enabled move support for Microsoft Visual Studio 2012.
        </li>
<li class="listitem">
          Added <code class="computeroutput">use_future</code> support for Microsoft Visual Studio 2012.
        </li>
<li class="listitem">
          Removed a use of <code class="computeroutput">std::min</code> in the Windows IOCP backend to avoid
          a dependency on the <code class="computeroutput">&lt;algorithm&gt;</code> header.
        </li>
<li class="listitem">
          Eliminated some unnecessary handler copies.
        </li>
<li class="listitem">
          Fixed support for older versions of OpenSSL that do not provide the <code class="computeroutput">SSL_CTX_clear_options</code>
          function.
        </li>
<li class="listitem">
          Fixed various minor and cosmetic issues in code and documentation.
        </li>
</ul></div>
<h4>
<a name="asio.history.h17"></a>
      <span><a name="asio.history.asio_1_10_0"></a></span><a class="link" href="history.html#asio.history.asio_1_10_0">Asio
      1.10.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added new traits classes, <code class="computeroutput">handler_type</code> and <code class="computeroutput">async_result</code>,
          that allow the customisation of the return type of an initiating function.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">asio::spawn()</code> function, a high-level wrapper for
          running stackful coroutines, based on the Boost.Coroutine library. The
          <code class="computeroutput">spawn()</code> function enables programs to implement asynchronous
          logic in a synchronous manner. For example: <code class="computeroutput">size_t n = my_socket.async_read_some(my_buffer,
          yield);</code>. For further information, see <a class="link" href="overview/core/spawn.html" title="Stackful Coroutines">Stackful
          Coroutines</a>.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">asio::use_future</code> special value, which provides first-class
          support for returning a C++11 <code class="computeroutput">std::future</code> from an asynchronous
          operation's initiating function. For example: <code class="computeroutput">future&lt;size_t&gt;
          = my_socket.async_read_some(my_buffer, asio::use_future);</code>. For further
          information, see <a class="link" href="overview/cpp2011/futures.html" title="Futures">C++ 2011
          Support - Futures</a>.
        </li>
<li class="listitem">
          Promoted the stackless coroutine class and macros to be part of Asio's
          documented interface, rather than part of the HTTP server 4 example. For
          further information, see <a class="link" href="overview/core/coroutine.html" title="Stackless Coroutines">Stackless
          Coroutines</a>.
        </li>
<li class="listitem">
          Added a new handler hook called <code class="computeroutput">asio_handler_is_continuation</code>.
          Asynchronous operations may represent a continuation of the asynchronous
          control flow associated with the current executing handler. The <code class="computeroutput">asio_handler_is_continuation</code>
          hook can be customised to return <code class="computeroutput">true</code> if this is the case,
          and Asio's implementation can use this knowledge to optimise scheduling
          of the new handler. To cover common cases, Asio customises the hook for
          strands, <code class="computeroutput">spawn()</code> and composed asynchronous operations.
        </li>
<li class="listitem">
          Added four new generic protocol classes, <code class="computeroutput">generic::datagram_protocol</code>,
          <code class="computeroutput">generic::raw_protocol</code>, <code class="computeroutput">generic::seq_packet_protocol</code>
          and <code class="computeroutput">generic::stream_protocol</code>, which implement the <code class="computeroutput">Protocol</code>
          type requirements, but allow the user to specify the address family (e.g.
          <code class="computeroutput">AF_INET</code>) and protocol type (e.g. <code class="computeroutput">IPPROTO_TCP</code>)
          at runtime. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Added C++11 move constructors that allow the conversion of a socket (or
          acceptor) into a more generic type. For example, an <code class="computeroutput">ip::tcp::socket</code>
          can be converted into a <code class="computeroutput">generic::stream_protocol::socket</code> via
          move construction. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput">basic_socket_acceptor&lt;&gt;</code>'s <code class="computeroutput">accept()</code>
          and <code class="computeroutput">async_accept()</code> functions to allow a new connection to
          be accepted directly into a socket of a more generic type. For example,
          an <code class="computeroutput">ip::tcp::acceptor</code> can be used to accept into a <code class="computeroutput">generic::stream_protocol::socket</code>
          object. For further information, see <a class="link" href="overview/networking/other_protocols.html" title="Support for Other Protocols">Support
          for Other Protocols</a>.
        </li>
<li class="listitem">
          Moved existing examples into a C++03-specific directory, and added a new
          directory for C++11-specific examples. A limited subset of the C++03 examples
          have been converted to their C++11 equivalents.
        </li>
<li class="listitem">
          Add the ability to use Asio without Boost, for a limited set of platforms.
          When using a C++11 compiler, most of Asio may now be used without a dependency
          on Boost header files or libraries. To use Asio in this way, define <code class="computeroutput">ASIO_STANDALONE</code>
          on your compiler command line or as part of the project options. This standalone
          configuration has currently been tested for the following platforms and
          compilers:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Linux with g++ 4.7 (requires <code class="literal">-std=c++11</code>)
              </li>
<li class="listitem">
                Mac OS X with clang++ / Xcode 4.6 (requires <code class="literal">-std=c++11 -stdlib=libc++</code>)
              </li>
</ul></div>
        </li>
<li class="listitem">
          Various SSL enhancements. Thanks go to Nick Jones, on whose work these
          changes are based.
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Added support for SSL handshakes with re-use of data already read
                from the wire. New overloads of the <code class="computeroutput">ssl::stream&lt;&gt;</code>
                class's <code class="computeroutput">handshake()</code> and <code class="computeroutput">async_handshake()</code>
                functions have been added. These accept a <code class="computeroutput">ConstBufferSequence</code>
                to be used as initial input to the ssl engine for the handshake procedure.
              </li>
<li class="listitem">
                Added support for creation of TLSv1.1 and TLSv1.2 <code class="computeroutput">ssl::context</code>
                objects.
              </li>
<li class="listitem">
                Added a <code class="computeroutput">set_verify_depth()</code> function to the <code class="computeroutput">ssl::context</code>
                and <code class="computeroutput">ssl::stream&lt;&gt;</code> classes.
              </li>
<li class="listitem">
                Added the ability to load SSL certificate and key data from memory
                buffers. New functions, <code class="computeroutput">add_certificate_authority()</code>,
                <code class="computeroutput">use_certificate()</code>, <code class="computeroutput">use_certificate_chain()</code>,
                <code class="computeroutput">use_private_key()</code>, <code class="computeroutput">use_rsa_private_key()</code>
                and <code class="computeroutput">use_tmp_dh()</code>, have been added to the <code class="computeroutput">ssl::context</code>
                class.
              </li>
<li class="listitem">
                Changed <code class="computeroutput">ssl::context</code> to automatically disable SSL compression
                by default. To enable, use the new <code class="computeroutput">ssl::context::clear_options()</code>
                function, as in <code class="computeroutput">my_context.clear_options(ssl::context::no_compression)</code>.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a potential deadlock in <code class="computeroutput">signal_set</code> implementation.
        </li>
<li class="listitem">
          Fixed an error in acceptor example in documentation.
        </li>
<li class="listitem">
          Fixed copy-paste errors in waitable timer documentation.
        </li>
<li class="listitem">
          Added assertions to satisfy some code analysis tools.
        </li>
<li class="listitem">
          Fixed a malformed <code class="computeroutput">#warning</code> directive.
        </li>
<li class="listitem">
          Fixed a potential data race in the Linux <code class="computeroutput">epoll</code> implementation.
        </li>
<li class="listitem">
          Fixed a Windows-specific bug, where certain operations might generate an
          <code class="computeroutput">error_code</code> with an invalid (i.e. <code class="computeroutput">NULL</code>) <code class="computeroutput">error_category</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">basic_waitable_timer</code>'s underlying implementation so
          that it can handle any <code class="computeroutput">time_point</code> value without overflowing
          the intermediate duration objects.
        </li>
<li class="listitem">
          Fixed a problem with lost thread wakeups that can occur when making concurrent
          calls to <code class="computeroutput">run()</code> and <code class="computeroutput">poll()</code> on the same <code class="computeroutput">io_service</code>
          object.
        </li>
<li class="listitem">
          Fixed implementation of asynchronous connect operation so that it can cope
          with spurious readiness notifications from the reactor.
        </li>
<li class="listitem">
          Fixed a memory leak in the <code class="computeroutput">ssl::rfc2818_verification</code> class.
        </li>
<li class="listitem">
          Added a mechanism for disabling automatic Winsock initialisation. See the
          header file <code class="literal">asio/detail/winsock_init.hpp</code> for details.
        </li>
</ul></div>
<h4>
<a name="asio.history.h18"></a>
      <span><a name="asio.history.asio_1_8_3"></a></span><a class="link" href="history.html#asio.history.asio_1_8_3">Asio
      1.8.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed some 64-to-32-bit conversion warnings.
        </li>
<li class="listitem">
          Fixed various small errors in documentation and comments.
        </li>
<li class="listitem">
          Fixed an error in the example embedded in <code class="computeroutput">basic_socket::get_option</code>'s
          documentation.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">long</code> rather than <code class="computeroutput">int</code> for SSL_CTX
          options, to match OpenSSL.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">_snwprintf</code> to address a compile error due to
          the changed <code class="computeroutput">swprintf</code> signature in recent versions of MinGW.
        </li>
<li class="listitem">
          Fixed a deadlock that can occur on Windows when shutting down a pool of
          <code class="computeroutput">io_service</code> threads due to running out of work.
        </li>
<li class="listitem">
          Changed UNIX domain socket example to treat errors from <code class="computeroutput">accept</code>
          as non-fatal.
        </li>
<li class="listitem">
          Added a small block recycling optimisation to improve default memory allocation
          behaviour.
        </li>
</ul></div>
<h4>
<a name="asio.history.h19"></a>
      <span><a name="asio.history.asio_1_8_2"></a></span><a class="link" href="history.html#asio.history.asio_1_8_2">Asio
      1.8.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed an incompatibility between <code class="computeroutput">ip::tcp::iostream</code> and C++11.
        </li>
<li class="listitem">
          Decorated GCC attribute names with underscores to prevent interaction with
          user-defined macros.
        </li>
<li class="listitem">
          Added missing <code class="computeroutput">#include &lt;cctype&gt;</code>, needed for some versions
          of MinGW.
        </li>
<li class="listitem">
          Changed to use <code class="literal">gcc</code>'s atomic builtins on ARM CPUs, when
          available.
        </li>
<li class="listitem">
          Changed strand destruction to be a no-op, to allow strand objects to be
          destroyed after their associated <code class="computeroutput">io_service</code> has been destroyed.
        </li>
<li class="listitem">
          Added support for some newer versions of glibc which provide the <code class="computeroutput">epoll_create1()</code>
          function but always fail with ENOSYS.
        </li>
<li class="listitem">
          Changed the SSL implementation to throw an exception if SSL engine initialisation
          fails.
        </li>
<li class="listitem">
          Fixed another regression in <code class="computeroutput">buffered_write_stream</code>.
        </li>
<li class="listitem">
          Implemented various minor performance improvements, primarily targeted
          at Linux x86 and x86-64 platforms.
        </li>
</ul></div>
<h4>
<a name="asio.history.h20"></a>
      <span><a name="asio.history.asio_1_8_1"></a></span><a class="link" href="history.html#asio.history.asio_1_8_1">Asio
      1.8.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Changed the <code class="computeroutput">epoll_reactor</code> backend to do lazy registration
          for <code class="computeroutput">EPOLLOUT</code> events.
        </li>
<li class="listitem">
          Fixed the <code class="computeroutput">epoll_reactor</code> handling of out-of-band data, which
          was broken by an incomplete fix in the last release.
        </li>
<li class="listitem">
          Changed Asio's SSL wrapper to respect OpenSSL's <code class="computeroutput">OPENSSL_NO_ENGINE</code>
          feature test <code class="computeroutput">#define</code>.
        </li>
<li class="listitem">
          Fixed <code class="computeroutput">windows::object_handle</code> so that it works with Windows
          compilers that support C++11 move semantics (such as <code class="literal">g++</code>).
        </li>
<li class="listitem">
          Improved the performance of strand rescheduling.
        </li>
<li class="listitem">
          Added support for <code class="literal">g++</code> 4.7 when compiling in C++11 mode.
        </li>
<li class="listitem">
          Fixed a problem where <code class="computeroutput">signal_set</code> handlers were not being delivered
          when the <code class="computeroutput">io_service</code> was constructed with a <code class="computeroutput">concurrency_hint</code>
          of 1.
        </li>
</ul></div>
<h4>
<a name="asio.history.h21"></a>
      <span><a name="asio.history.asio_1_8_0"></a></span><a class="link" href="history.html#asio.history.asio_1_8_0">Asio
      1.8.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new class template <code class="computeroutput">basic_waitable_timer</code> based around
          the C++11 clock type requirements. It may be used with the clocks from
          the C++11 <code class="computeroutput">&lt;chrono&gt;</code> library facility or, if those are
          not available, Boost.Chrono. The typedefs <code class="computeroutput">high_resolution_timer</code>,
          <code class="computeroutput">steady_timer</code> and <code class="computeroutput">system_timer</code> may be used to
          create timer objects for the standard clock types.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">windows::object_handle</code> class for performing waits
          on Windows kernel objects. Thanks go to Boris Schaeling for contributing
          substantially to the development of this feature.
        </li>
<li class="listitem">
          On Linux, <code class="computeroutput">connect()</code> can return EAGAIN in certain circumstances.
          Remapped this to another error so that it doesn't look like a non-blocking
          operation.
        </li>
<li class="listitem">
          Fixed a compile error on NetBSD.
        </li>
<li class="listitem">
          Fixed deadlock on Mac OS X.
        </li>
<li class="listitem">
          Fixed a regression in <code class="computeroutput">buffered_write_stream</code>.
        </li>
<li class="listitem">
          Fixed a non-paged pool "leak" on Windows when an <code class="computeroutput">io_service</code>
          is repeatedly run without anything to do.
        </li>
<li class="listitem">
          Reverted earlier change to allow some speculative operations to be performed
          without holding the lock, as it introduced a race condition in some multithreaded
          scenarios.
        </li>
<li class="listitem">
          Fixed a bug where the second buffer in an array of two buffers may be ignored
          if the first buffer is empty.
        </li>
</ul></div>
<h4>
<a name="asio.history.h22"></a>
      <span><a name="asio.history.asio_1_6_1"></a></span><a class="link" href="history.html#asio.history.asio_1_6_1">Asio
      1.6.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implemented various performance improvements, including:
          <div class="itemizedlist"><ul class="itemizedlist" type="circle">
<li class="listitem">
                Using thread-local operation queues in single-threaded use cases
                (i.e. when <code class="computeroutput">concurrency_hint</code> is 1) to eliminate a lock/unlock
                pair.
              </li>
<li class="listitem">
                Allowing some <code class="computeroutput">epoll_reactor</code> speculative operations to
                be performed without holding the lock.
              </li>
<li class="listitem">
                Improving locality of reference by performing an <code class="computeroutput">epoll_reactor</code>'s
                I/O operation immediately before the corresponding handler is called.
                This also improves scalability across CPUs when multiple threads
                are running the <code class="computeroutput">io_service</code>.
              </li>
<li class="listitem">
                Specialising asynchronous read and write operations for buffer sequences
                that are arrays (<code class="computeroutput">boost::array</code> or <code class="computeroutput">std::array</code>)
                of exactly two buffers.
              </li>
</ul></div>
        </li>
<li class="listitem">
          Fixed a compile error in the regex overload of <code class="computeroutput">async_read_until</code>.
        </li>
<li class="listitem">
          Fixed a Windows-specific compile error by explicitly specifying the <code class="computeroutput">signal()</code>
          function from the global namespace.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">deadline_timer</code> implementation so that it does
          not read the clock unless the timer heap is non-empty.
        </li>
<li class="listitem">
          Changed the SSL stream's buffers' sizes so that they are large enough to
          hold a complete TLS record.
        </li>
<li class="listitem">
          Fixed the behaviour of the synchronous <code class="computeroutput">null_buffers</code> operations
          so that they obey the user's non-blocking setting.
        </li>
<li class="listitem">
          Changed to set the size of the select <code class="computeroutput">fd_set</code> at runtime when
          using Windows.
        </li>
<li class="listitem">
          Disabled an MSVC warning due to const qualifier being applied to function
          type.
        </li>
<li class="listitem">
          Fixed a crash that occurs when using the Intel C++ compiler.
        </li>
<li class="listitem">
          Changed the initialisation of the OpenSSL library so that it supports all
          available algorithms.
        </li>
<li class="listitem">
          Fixed the SSL error mapping used when the session is gracefully shut down.
        </li>
<li class="listitem">
          Added some latency test programs.
        </li>
<li class="listitem">
          Clarified that a read operation ends when the buffer is full.
        </li>
<li class="listitem">
          Fixed an exception safety issue in <code class="computeroutput">epoll_reactor</code> initialisation.
        </li>
<li class="listitem">
          Made the number of strand implementations configurable by defining <code class="computeroutput">(BOOST_)ASIO_STRAND_IMPLEMENTATIONS</code>
          to the desired number.
        </li>
<li class="listitem">
          Added support for a new <code class="computeroutput">(BOOST_)ASIO_ENABLE_SEQUENTIAL_STRAND_ALLOCATION</code>
          flag which switches the allocation of strand implementations to use a round-robin
          approach rather than hashing.
        </li>
<li class="listitem">
          Fixed potential strand starvation issue that can occur when <code class="computeroutput">strand.post()</code>
          is used.
        </li>
</ul></div>
<h4>
<a name="asio.history.h23"></a>
      <span><a name="asio.history.asio_1_6_0"></a></span><a class="link" href="history.html#asio.history.asio_1_6_0">Asio
      1.6.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved support for C++0x move construction to further reduce copying
          of handler objects. In certain designs it is possible to eliminate virtually
          all copies. Move support is now enabled when compiling in <code class="literal">-std=c++0x</code>
          mode on g++ 4.5 or higher.
        </li>
<li class="listitem">
          Added build support for platforms that don't provide either of <code class="computeroutput">signal()</code>
          or <code class="computeroutput">sigaction()</code>.
        </li>
<li class="listitem">
          Changed to use C++0x variadic templates when they are available, rather
          than generating function overloads using the Boost.Preprocessor library.
        </li>
<li class="listitem">
          Ensured the value of <code class="computeroutput">errno</code> is preserved across the implementation's
          signal handler.
        </li>
<li class="listitem">
          On Windows, ensured the count of outstanding work is decremented for abandoned
          operations (i.e. operations that are being cleaned up within the <code class="computeroutput">io_service</code>
          destructor).
        </li>
<li class="listitem">
          Fixed behaviour of zero-length reads and writes in the new SSL implementation.
        </li>
<li class="listitem">
          Added support for building with OpenSSL 1.0 when <code class="computeroutput">OPENSSL_NO_SSL2</code>
          is defined.
        </li>
<li class="listitem">
          Changed most examples to treat a failure by an accept operation as non-fatal.
        </li>
<li class="listitem">
          Fixed an error in the <code class="literal">tick_count_timer</code> example by making
          the duration type signed. Previously, a wait on an already-passed deadline
          would not return for a very long time.
        </li>
</ul></div>
<h4>
<a name="asio.history.h24"></a>
      <span><a name="asio.history.asio_1_5_3"></a></span><a class="link" href="history.html#asio.history.asio_1_5_3">Asio
      1.5.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new, completely rewritten SSL implementation. The new implementation
          compiles faster, shows substantially improved performance, and supports
          custom memory allocation and handler invocation. It includes new API features
          such as certificate verification callbacks and has improved error reporting.
          The new implementation is source-compatible with the old for most uses.
          However, if necessary, the old implementation may still be used by defining
          <code class="computeroutput">(BOOST_)ASIO_ENABLE_OLD_SSL</code>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">asio::buffer()</code> overloads for <code class="computeroutput">std::array</code>,
          when available. The support is automatically enabled when compiling in
          <code class="literal">-std=c++0x</code> mode on g++ 4.3 or higher, or when using
          MSVC 10. The support may be explicitly enabled by defining <code class="computeroutput">(BOOST_)ASIO_HAS_STD_ARRAY</code>,
          or disabled by defining <code class="computeroutput">(BOOST_)ASIO_DISABLE_STD_ARRAY</code>.
        </li>
<li class="listitem">
          Changed to use the C++0x standard library templates <code class="computeroutput">array</code>,
          <code class="computeroutput">shared_ptr</code>, <code class="computeroutput">weak_ptr</code> and <code class="computeroutput">atomic</code>
          when they are available, rather than the Boost equivalents.
        </li>
<li class="listitem">
          Support for <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>
          is no longer enabled by default for g++ 4.5, as that compiler's standard
          library does not implement <code class="computeroutput">std::system_error::what()</code> correctly.
        </li>
</ul></div>
<h4>
<a name="asio.history.h25"></a>
      <span><a name="asio.history.asio_1_5_2"></a></span><a class="link" href="history.html#asio.history.asio_1_5_2">Asio
      1.5.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for C++0x move construction and assignment to sockets, serial
          ports, POSIX descriptors and Windows handles.
        </li>
<li class="listitem">
          Added support for the <code class="computeroutput">fork()</code> system call. Programs that use
          <code class="computeroutput">fork()</code> must call <code class="computeroutput">io_service.notify_fork()</code> at
          the appropriate times. Two new examples have been added showing how to
          use this feature.
        </li>
<li class="listitem">
          Cleaned up the handling of errors reported by the <code class="computeroutput">close()</code>
          system call. In particular, assume that most operating systems won't have
          <code class="computeroutput">close()</code> fail with <code class="computeroutput">EWOULDBLOCK</code>, but if it does
          then set the blocking mode and restart the call. If any other error occurs,
          assume the descriptor is closed.
        </li>
<li class="listitem">
          The kqueue flag <code class="computeroutput">EV_ONESHOT</code> seems to cause problems on some
          versions of Mac OS X, with the <code class="computeroutput">io_service</code> destructor getting
          stuck inside the <code class="computeroutput">close()</code> system call. Changed the kqueue backend
          to use <code class="computeroutput">EV_CLEAR</code> instead.
        </li>
<li class="listitem">
          Changed exception reporting to include the function name in exception
          <code class="computeroutput">what()</code> messages.
        </li>
<li class="listitem">
          Fixed an insufficient initialisers warning with MinGW.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">shutdown_service()</code> member functions to be private.
        </li>
<li class="listitem">
          Added archetypes for testing socket option functions.
        </li>
<li class="listitem">
          Added a missing lock in <code class="computeroutput">signal_set_service::cancel()</code>.
        </li>
<li class="listitem">
          Fixed a copy/paste error in <code class="computeroutput">SignalHandler</code> example.
        </li>
<li class="listitem">
          Added the inclusion of the signal header to <code class="computeroutput">signal_set_service.hpp</code>
          so that constants like <code class="computeroutput">NSIG</code> may be used.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">signal_set_service</code> implementation so that it doesn't
          assume that <code class="computeroutput">SIGRTMAX</code> is a compile-time constant.
        </li>
<li class="listitem">
          Changed the Boost.Asio examples so that they don't use Boost.Thread's convenience
          header. Use the header file that is specifically for the boost::thread
          class instead.
        </li>
</ul></div>
<h4>
<a name="asio.history.h26"></a>
      <span><a name="asio.history.asio_1_5_1"></a></span><a class="link" href="history.html#asio.history.asio_1_5_1">Asio
      1.5.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for signal handling, using a new class called <code class="computeroutput">signal_set</code>.
          Programs may add one or more signals to the set, and then perform an <code class="computeroutput">async_wait()</code>
          operation. The specified handler will be called when one of the signals
          occurs. The same signal number may registered with multiple <code class="computeroutput">signal_set</code>
          objects, however the signal number must be used only with Asio.
        </li>
<li class="listitem">
          Added handler tracking, a new debugging aid. When enabled by defining
          <code class="computeroutput">(BOOST_)ASIO_ENABLE_HANDLER_TRACKING</code>, Asio writes debugging
          output to the standard error stream. The output records asynchronous operations
          and the relationships between their handlers. It may be post-processed
          using the included <code class="literal">handlerviz.pl</code> tool to create a visual
          representation of the handlers (requires GraphViz).
        </li>
<li class="listitem">
          Fixed a bug in <code class="computeroutput">asio::streambuf</code> where the <code class="computeroutput">consume()</code>
          function did not always update the internal buffer pointers correctly.
          The problem may occur when the <code class="computeroutput">asio::streambuf</code> is filled with
          data using the standard C++ member functions such as <code class="computeroutput">sputn()</code>.
          (Note: the problem does not manifest when the streambuf is populated by
          the Asio free functions <code class="computeroutput">read()</code>, <code class="computeroutput">async_read()</code>,
          <code class="computeroutput">read_until()</code> or <code class="computeroutput">async_read_until()</code>.)
        </li>
<li class="listitem">
          Fixed a bug on kqueue-based platforms, where reactor read operations that
          return false from their <code class="computeroutput">perform()</code> function are not correctly
          re-registered with kqueue.
        </li>
<li class="listitem">
          Support for <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>
          is no longer enabled by default for MSVC10, as that compiler's standard
          library does not implement <code class="computeroutput">std::system_error::what()</code> correctly.
        </li>
<li class="listitem">
          Modified the <code class="computeroutput">buffers_iterator&lt;&gt;</code> and <code class="computeroutput">ip::basic_resolver_iterator</code>
          classes so that the value_type typedefs are non-const byte types.
        </li>
</ul></div>
<h4>
<a name="asio.history.h27"></a>
      <span><a name="asio.history.asio_1_5_0"></a></span><a class="link" href="history.html#asio.history.asio_1_5_0">Asio
      1.5.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for timeouts on socket iostreams, such as <code class="computeroutput">ip::tcp::iostream</code>.
          A timeout is set by calling <code class="computeroutput">expires_at()</code> or <code class="computeroutput">expires_from_now()</code>
          to establish a deadline. Any socket operations which occur past the deadline
          will put the iostream into a bad state.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">error()</code> member function to socket iostreams, for
          retrieving the error code from the most recent system call.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">basic_deadline_timer::cancel_one()</code> function. This
          function lets you cancel a single waiting handler on a timer. Handlers
          are cancelled in FIFO order.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">transfer_exactly()</code> completion condition. This
          can be used to send or receive a specified number of bytes even if the
          total size of the buffer (or buffer sequence) is larger.
        </li>
<li class="listitem">
          Added new free functions <code class="computeroutput">connect()</code> and <code class="computeroutput">async_connect()</code>.
          These operations try each endpoint in a list until the socket is successfully
          connected.
        </li>
<li class="listitem">
          Extended the <code class="computeroutput">buffer_size()</code> function so that it works for buffer
          sequences in addition to individual buffers.
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">buffer_copy()</code> function that can be used to copy
          the raw bytes between individual buffers and buffer sequences.
        </li>
<li class="listitem">
          Added new non-throwing overloads of <code class="computeroutput">read()</code>, <code class="computeroutput">read_at()</code>,
          <code class="computeroutput">write()</code> and <code class="computeroutput">write_at()</code> that do not require a
          completion condition.
        </li>
<li class="listitem">
          Added friendlier compiler errors for when a completion handler does not
          meet the necessary type requirements. When C++0x is available (currently
          supported for g++ 4.5 or later, and MSVC 10), <code class="computeroutput">static_assert</code>
          is also used to generate an informative error message. This checking may
          be disabled by defining <code class="computeroutput">(BOOST_)ASIO_DISABLE_HANDLER_TYPE_REQUIREMENTS</code>.
        </li>
<li class="listitem">
          Added support for using <code class="computeroutput">std::error_code</code> and <code class="computeroutput">std::system_error</code>,
          when available. The support is automatically enabled when compiling in
          <code class="literal">-std=c++0x</code> mode on g++ 4.5 or higher, or when using
          MSVC 10. The support may be explicitly enabled by defining <code class="computeroutput">ASIO_HAS_STD_SYSTEM_ERROR</code>,
          or disabled by defining <code class="computeroutput">ASIO_DISABLE_STD_SYSTEM_ERROR</code>. (Available
          in non-Boost version of Asio only.)
        </li>
<li class="listitem">
          Made the <code class="computeroutput">is_loopback()</code>, <code class="computeroutput">is_unspecified()</code> and
          <code class="computeroutput">is_multicast()</code> functions consistently available across the
          <code class="computeroutput">ip::address</code>, <code class="computeroutput">ip::address_v4</code> and <code class="computeroutput">ip::address_v6</code>
          classes.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">non_blocking()</code> functions for managing the non-blocking
          behaviour of a socket or descriptor. The <code class="computeroutput">io_control()</code> commands
          named <code class="computeroutput">non_blocking_io</code> are now deprecated in favour of these
          new functions.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">native_non_blocking()</code> functions for managing the
          non-blocking mode of the underlying socket or descriptor. These functions
          are intended to allow the encapsulation of arbitrary non-blocking system
          calls as asynchronous operations, in a way that is transparent to the user
          of the socket object. The functions have no effect on the behaviour of
          the synchronous operations of the socket or descriptor.
        </li>
<li class="listitem">
          Added the <code class="computeroutput">io_control()</code> member function for socket acceptors.
        </li>
<li class="listitem">
          For consistency with the C++0x standard library, deprecated the <code class="computeroutput">native_type</code>
          typedefs in favour of <code class="computeroutput">native_handle_type</code>, and the <code class="computeroutput">native()</code>
          member functions in favour of <code class="computeroutput">native_handle()</code>.
        </li>
<li class="listitem">
          Added a <code class="computeroutput">release()</code> member function to posix descriptors. This
          function releases ownership of the underlying native descriptor to the
          caller.
        </li>
<li class="listitem">
          Added support for sequenced packet sockets (<code class="computeroutput">SOCK_SEQPACKET</code>).
        </li>
<li class="listitem">
          Added a new <code class="computeroutput">io_service::stopped()</code> function that can be used
          to determine whether the <code class="computeroutput">io_service</code> has stopped (i.e. a <code class="computeroutput">reset()</code>
          call is needed prior to any further calls to <code class="computeroutput">run()</code>, <code class="computeroutput">run_one()</code>,
          <code class="computeroutput">poll()</code> or <code class="computeroutput">poll_one()</code>).
        </li>
<li class="listitem">
          Reduced the copying of handler function objects.
        </li>
<li class="listitem">
          Added support for C++0x move construction to further reduce copying of
          handler objects. Move support is enabled when compiling in <code class="literal">-std=c++0x</code>
          mode on g++ 4.5 or higher, or when using MSVC10.
        </li>
<li class="listitem">
          Removed the dependency on OS-provided macros for the well-known IPv4 and
          IPv6 addresses. This should eliminate the annoying "missing braces
          around initializer" warnings.
        </li>
<li class="listitem">
          Reduced the size of <code class="computeroutput">ip::basic_endpoint&lt;&gt;</code> objects (such
          as <code class="computeroutput">ip::tcp::endpoint</code> and <code class="computeroutput">ip::udp::endpoint</code>).
        </li>
<li class="listitem">
          Changed the reactor backends to assume that any descriptors or sockets
          added using <code class="computeroutput">assign()</code> may have been <code class="computeroutput">dup()</code>-ed,
          and so require explicit deregistration from the reactor.
        </li>
<li class="listitem">
          Changed the SSL error category to return error strings from the OpenSSL
          library.
        </li>
<li class="listitem">
          Changed the separate compilation support such that, to use Asio's SSL capabilities,
          you should also include 'asio/ssl/impl/src.hpp` in one source file in your
          program.
        </li>
<li class="listitem">
          Removed the deprecated member functions named <code class="computeroutput">io_service()</code>.
          The <code class="computeroutput">get_io_service()</code> member functions should be used instead.
        </li>
<li class="listitem">
          Removed the deprecated typedefs <code class="computeroutput">resolver_query</code> and <code class="computeroutput">resolver_iterator</code>
          from the <code class="computeroutput">ip::tcp</code>, <code class="computeroutput">ip::udp</code> and <code class="computeroutput">ip::icmp</code>
          classes.
        </li>
<li class="listitem">
          Fixed a compile error on some versions of g++ due to anonymous enums.
        </li>
<li class="listitem">
          Added an explicit cast to the <code class="computeroutput">FIONBIO</code> constant to int to suppress
          a compiler warning on some platforms.
        </li>
<li class="listitem">
          Fixed warnings reported by g++'s <code class="literal">-Wshadow</code> compiler option.
        </li>
</ul></div>
<h4>
<a name="asio.history.h28"></a>
      <span><a name="asio.history.asio_1_4_8"></a></span><a class="link" href="history.html#asio.history.asio_1_4_8">Asio
      1.4.8</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed an integer overflow problem that occurs when <code class="computeroutput">ip::address_v4::broadcast()</code>
          is used on 64-bit platforms.
        </li>
<li class="listitem">
          Fixed a problem on older Linux kernels (where epoll is used without <code class="computeroutput">timerfd</code>
          support) that prevents timely delivery of <code class="computeroutput">deadline_timer</code> handlers,
          after the program has been running for some time.
        </li>
</ul></div>
<h4>
<a name="asio.history.h29"></a>
      <span><a name="asio.history.asio_1_4_7"></a></span><a class="link" href="history.html#asio.history.asio_1_4_7">Asio
      1.4.7</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Fixed a problem on kqueue-based platforms where a <code class="computeroutput">deadline_timer</code>
          may never fire if the <code class="computeroutput">io_service</code> is running in a background
          thread.
        </li>
<li class="listitem">
          Fixed a const-correctness issue that prevented valid uses of <code class="computeroutput">has_service&lt;&gt;</code>
          from compiling.
        </li>
<li class="listitem">
          Fixed MinGW cross-compilation.
        </li>
<li class="listitem">
          Removed dependency on deprecated Boost.System functions (Boost.Asio only).
        </li>
<li class="listitem">
          Ensured <code class="computeroutput">close()</code>/<code class="computeroutput">closesocket()</code> failures are correctly
          propagated.
        </li>
<li class="listitem">
          Added a check for errors returned by <code class="computeroutput">InitializeCriticalSectionAndSpinCount</code>.
        </li>
<li class="listitem">
          Added support for hardware flow control on QNX.
        </li>
<li class="listitem">
          Always use <code class="computeroutput">pselect()</code> on HP-UX, if it is available.
        </li>
<li class="listitem">
          Ensured handler arguments are passed as lvalues.
        </li>
<li class="listitem">
          Fixed Windows build when thread support is disabled.
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where <code class="computeroutput">deadline_timer</code> objects
          with expiry times set more than 5 minutes in the future may never expire.
        </li>
<li class="listitem">
          Fixed the resolver backend on BSD platforms so that an empty service name
          resolves to port number <code class="computeroutput">0</code>, as per the documentation.
        </li>
<li class="listitem">
          Fixed read operations so that they do not accept buffer sequences of type
          <code class="computeroutput">const_buffers_1</code>.
        </li>
<li class="listitem">
          Redefined <code class="computeroutput">Protocol</code> and <code class="computeroutput">id</code> to avoid clashing with
          Objective-C++ keywords.
        </li>
<li class="listitem">
          Fixed a <code class="computeroutput">vector</code> reallocation performance issue that can occur
          when there are many active <code class="computeroutput">deadline_timer</code> objects.
        </li>
<li class="listitem">
          Fixed the kqueue backend so that it compiles on NetBSD.
        </li>
<li class="listitem">
          Fixed the socket <code class="computeroutput">io_control()</code> implementation on 64-bit Mac
          OS X and BSD platforms.
        </li>
<li class="listitem">
          Fixed a Windows-specific problem where failures from <code class="computeroutput">accept()</code>
          are incorrectly treated as successes.
        </li>
<li class="listitem">
          Deprecated the separate compilation header <code class="computeroutput">asio/impl/src.cpp</code>
          in favour of <code class="computeroutput">asio/impl/src.hpp</code>.
        </li>
</ul></div>
<h4>
<a name="asio.history.h30"></a>
      <span><a name="asio.history.asio_1_4_6"></a></span><a class="link" href="history.html#asio.history.asio_1_4_6">Asio
      1.4.6</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Reduced compile times. (Note that some programs may need to add additional
          <code class="computeroutput">#include</code>s, e.g. if the program uses boost::array but does
          not explicitly include <code class="computeroutput">&lt;boost/array.hpp&gt;</code>.)
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Refactored <code class="computeroutput">deadline_timer</code> implementation to improve performance.
        </li>
<li class="listitem">
          Improved multiprocessor scalability on Windows by using a dedicated hidden
          thread to wait for timers.
        </li>
<li class="listitem">
          Improved performance of <code class="computeroutput">asio::streambuf</code> with <code class="computeroutput">async_read()</code>
          and <code class="computeroutput">async_read_until()</code>. These read operations now use the
          existing capacity of the <code class="computeroutput">streambuf</code> when reading, rather than
          limiting the read to 512 bytes.
        </li>
<li class="listitem">
          Added optional separate compilation. To enable, include <code class="computeroutput">asio/impl/src.cpp</code>
          in one source file in a program, then build the program with <code class="computeroutput">(BOOST_)ASIO_SEPARATE_COMPILATION</code>
          defined in the project/compiler settings. Alternatively, <code class="computeroutput">(BOOST_)ASIO_DYN_LINK</code>
          may be defined to build a separately-compiled Asio as part of a shared
          library.
        </li>
<li class="listitem">
          Added new macro <code class="computeroutput">(BOOST_)ASIO_DISABLE_FENCED_BLOCK</code> to permit
          the disabling of memory fences around completion handlers, even if thread
          support is enabled.
        </li>
<li class="listitem">
          Reworked timeout examples to better illustrate typical use cases.
        </li>
<li class="listitem">
          Ensured that handler arguments are passed as const types.
        </li>
<li class="listitem">
          Fixed incorrect parameter order in <code class="computeroutput">null_buffers</code> variant of
          <code class="computeroutput">async_send_to</code>.
        </li>
<li class="listitem">
          Ensured unsigned char is used with <code class="computeroutput">isdigit</code> in <code class="computeroutput">getaddrinfo</code>
          emulation.
        </li>
<li class="listitem">
          Fixed handling of very small but non-zero timeouts.
        </li>
<li class="listitem">
          Fixed crash that occurred when an empty buffer sequence was passed to a
          composed read or write operation.
        </li>
<li class="listitem">
          Added missing operator+ overload in <code class="computeroutput">buffers_iterator</code>.
        </li>
<li class="listitem">
          Implemented cancellation of <code class="computeroutput">null_buffers</code> operations on Windows.
        </li>
</ul></div>
<h4>
<a name="asio.history.h31"></a>
      <span><a name="asio.history.asio_1_4_5"></a></span><a class="link" href="history.html#asio.history.asio_1_4_5">Asio
      1.4.5</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved performance.
        </li>
<li class="listitem">
          Reduced compile times.
        </li>
<li class="listitem">
          Reduced the size of generated code.
        </li>
<li class="listitem">
          Extended the guarantee that background threads don't call user code to
          all asynchronous operations.
        </li>
<li class="listitem">
          Changed to use edge-triggered epoll on Linux.
        </li>
<li class="listitem">
          Changed to use <code class="computeroutput">timerfd</code> for dispatching timers on Linux, when
          available.
        </li>
<li class="listitem">
          Changed to use one-shot notifications with kqueue on Mac OS X and BSD platforms.
        </li>
<li class="listitem">
          Added a bitmask type <code class="computeroutput">ip::resolver_query_base::flags</code> as per
          the TR2 proposal. This type prevents implicit conversion from <code class="computeroutput">int</code>
          to <code class="computeroutput">flags</code>, allowing the compiler to catch cases where users
          incorrectly pass a numeric port number as the service name.
        </li>
<li class="listitem">
          Added <code class="computeroutput">#define NOMINMAX</code> for all Windows compilers. Users can
          define <code class="computeroutput">(BOOST_)ASIO_NO_NOMINMAX</code> to suppress this definition.
        </li>
<li class="listitem">
          Fixed a bug where 0-byte asynchronous reads were incorrectly passing an
          <code class="computeroutput">error::eof</code> result to the completion handler.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">io_control()</code> member functions to always call
          <code class="computeroutput">ioctl</code> on the underlying descriptor when modifying blocking
          mode.
        </li>
<li class="listitem">
          Changed the resolver implementation so that it no longer requires the typedefs
          <code class="computeroutput">InternetProtocol::resolver_query</code> and <code class="computeroutput">InternetProtocol::resolver_iterator</code>,
          as neither typedef is part of the documented <code class="computeroutput">InternetProtocol</code>
          requirements. The corresponding typedefs in the <code class="computeroutput">ip::tcp</code>,
          <code class="computeroutput">ip::udp</code> and <code class="computeroutput">ip::icmp</code> classes have been deprecated.
        </li>
<li class="listitem">
          Fixed out-of-band handling for reactors not based on <code class="computeroutput">select()</code>.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">(BOOST_)ASIO_DISABLE_THREADS</code> macro that allows Asio's
          threading support to be independently disabled.
        </li>
<li class="listitem">
          Minor documentation improvements.
        </li>
</ul></div>
<h4>
<a name="asio.history.h32"></a>
      <span><a name="asio.history.asio_1_4_4"></a></span><a class="link" href="history.html#asio.history.asio_1_4_4">Asio
      1.4.4</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new HTTP Server 4 example illustrating the use of stackless coroutines
          with Asio.
        </li>
<li class="listitem">
          Changed handler allocation and invocation to use <code class="computeroutput">boost::addressof</code>
          to get the address of handler objects, rather than applying <code class="computeroutput">operator&amp;</code>
          directly.
        </li>
<li class="listitem">
          Restricted MSVC buffer debugging workaround to 2008, as it causes a crash
          with 2010 beta 2.
        </li>
<li class="listitem">
          Fixed a problem with the lifetime of handler memory, where Windows needs
          the <code class="computeroutput">OVERLAPPED</code> structure to be valid until both the initiating
          function call has returned and the completion packet has been delivered.
        </li>
<li class="listitem">
          Don't block signals while performing system calls, but instead restart
          the calls if they are interrupted.
        </li>
<li class="listitem">
          Documented the guarantee made by strand objects with respect to order of
          handler invocation.
        </li>
<li class="listitem">
          Changed strands to use a pool of implementations, to make copying of strands
          cheaper.
        </li>
<li class="listitem">
          Ensured that kqueue support is enabled for BSD platforms.
        </li>
<li class="listitem">
          Added a <code class="computeroutput">boost_</code> prefix to the <code class="computeroutput">extern "C"</code>
          thread entry point function.
        </li>
<li class="listitem">
          In <code class="computeroutput">getaddrinfo</code> emulation, only check the socket type (<code class="computeroutput">SOCK_STREAM</code>
          or <code class="computeroutput">SOCK_DGRAM</code>) if a service name has been specified. This
          should allow the emulation to work with raw sockets.
        </li>
<li class="listitem">
          Added a workaround for some broken Windows firewalls that make a socket
          appear bound to 0.0.0.0 when it is in fact bound to 127.0.0.1.
        </li>
<li class="listitem">
          Applied a fix for reported excessive CPU usage under Solaris.
        </li>
<li class="listitem">
          Added some support for platforms that use older compilers such as g++ 2.95.
        </li>
</ul></div>
<h4>
<a name="asio.history.h33"></a>
      <span><a name="asio.history.asio_1_4_3"></a></span><a class="link" href="history.html#asio.history.asio_1_4_3">Asio
      1.4.3</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added a new ping example to illustrate the use of ICMP sockets.
        </li>
<li class="listitem">
          Changed the <code class="computeroutput">buffered*_stream&lt;&gt;</code> templates to treat 0-byte
          reads and writes as no-ops, to comply with the documented type requirements
          for <code class="computeroutput">SyncReadStream</code>, <code class="computeroutput">AsyncReadStream</code>, <code class="computeroutput">SyncWriteStream</code>
          and <code class="computeroutput">AsyncWriteStream</code>.
        </li>
<li class="listitem">
          Changed some instances of the <code class="computeroutput">throw</code> keyword to <code class="computeroutput">boost::throw_exception()</code>
          to allow Asio to be used when exception support is disabled. Note that
          the SSL wrappers still require exception support.
        </li>
<li class="listitem">
          Made Asio compatible with the OpenSSL 1.0 beta.
        </li>
<li class="listitem">
          Eliminated a redundant system call in the Solaris /dev/poll backend.
        </li>
<li class="listitem">
          Fixed a bug in resizing of the bucket array in the internal hash maps.
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous accept
          fails.
        </li>
<li class="listitem">
          Ensured correct propagation of the error code when a synchronous read or
          write on a Windows <code class="computeroutput">HANDLE</code> fails.
        </li>
<li class="listitem">
          Fixed failures reported when <code class="computeroutput">_GLIBCXX_DEBUG</code> is defined.
        </li>
<li class="listitem">
          Fixed custom memory allocation support for timers.
        </li>
<li class="listitem">
          Tidied up various warnings reported by g++.
        </li>
<li class="listitem">
          Various documentation improvements, including more obvious hyperlinks to
          function overloads, header file information, examples for the handler type
          requirements, and adding enum values to the index.
        </li>
</ul></div>
<h4>
<a name="asio.history.h34"></a>
      <span><a name="asio.history.asio_1_4_2"></a></span><a class="link" href="history.html#asio.history.asio_1_4_2">Asio
      1.4.2</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Implement automatic resizing of the bucket array in the internal hash maps.
          This is to improve performance for very large numbers of asynchronous operations
          and also to reduce memory usage for very small numbers. A new macro <code class="computeroutput">(BOOST_)ASIO_HASH_MAP_BUCKETS</code>
          may be used to tweak the sizes used for the bucket arrays. (N.B. this feature
          introduced a bug which was fixed in Asio 1.4.3 / Boost 1.40.)
        </li>
<li class="listitem">
          Add performance optimisation for the Windows IOCP backend for when no timers
          are used.
        </li>
<li class="listitem">
          Prevent locale settings from affecting formatting of TCP and UDP endpoints.
        </li>
<li class="listitem">
          Fix a memory leak that occurred when an asynchronous SSL operation's completion
          handler threw an exception.
        </li>
<li class="listitem">
          Fix the implementation of <code class="computeroutput">io_control()</code> so that it adheres
          to the documented type requirements for IoControlCommand.
        </li>
<li class="listitem">
          Fix incompatibility between Asio and ncurses.h.
        </li>
<li class="listitem">
          On Windows, specifically handle the case when an overlapped <code class="computeroutput">ReadFile</code>
          call fails with <code class="computeroutput">ERROR_MORE_DATA</code>. This enables a hack where
          a <code class="computeroutput">windows::stream_handle</code> can be used with a message-oriented
          named pipe.
        </li>
<li class="listitem">
          Fix system call wrappers to always clear the error on success, as POSIX
          allows successful system calls to modify errno.
        </li>
<li class="listitem">
          Don't include termios.h if <code class="computeroutput">(BOOST_)ASIO_DISABLE_SERIAL_PORT</code>
          is defined.
        </li>
<li class="listitem">
          Cleaned up some more MSVC level 4 warnings.
        </li>
<li class="listitem">
          Various documentation fixes.
        </li>
</ul></div>
<h4>
<a name="asio.history.h35"></a>
      <span><a name="asio.history.asio_1_4_1"></a></span><a class="link" href="history.html#asio.history.asio_1_4_1">Asio
      1.4.1</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Improved compatibility with some Windows firewall software.
        </li>
<li class="listitem">
          Ensured arguments to <code class="computeroutput">windows::overlapped_ptr::complete()</code> are
          correctly passed to the completion handler.
        </li>
<li class="listitem">
          Fixed a link problem and multicast failure on QNX.
        </li>
<li class="listitem">
          Fixed a compile error in SSL support on MinGW / g++ 3.4.5.
        </li>
<li class="listitem">
          Drop back to using a pipe for notification if eventfd is not available
          at runtime on Linux.
        </li>
<li class="listitem">
          Various minor bug and documentation fixes.
        </li>
</ul></div>
<h4>
<a name="asio.history.h36"></a>
      <span><a name="asio.history.asio_1_4_0"></a></span><a class="link" href="history.html#asio.history.asio_1_4_0">Asio
      1.4.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Enhanced CompletionCondition concept with the signature <code class="computeroutput">size_t CompletionCondition(error_code
          ec, size_t total)</code>, where the return value indicates the maximum
          number of bytes to be transferred on the next read or write operation.
          (The old CompletionCondition signature is still supported for backwards
          compatibility).
        </li>
<li class="listitem">
          New <code class="computeroutput">windows::overlapped_ptr</code> class to allow arbitrary overlapped
          I/O functions (such as <code class="computeroutput">TransmitFile</code>) to be used with Asio.
        </li>
<li class="listitem">
          On recent versions of Linux, an <code class="computeroutput">eventfd</code> descriptor is now
          used (rather than a pipe) to interrupt a blocked select/epoll reactor.
        </li>
<li class="listitem">
          Added const overloads of <code class="computeroutput">lowest_layer()</code>.
        </li>
<li class="listitem">
          Synchronous read, write, accept and connect operations are now thread safe
          (meaning that it is now permitted to perform concurrent synchronous operations
          on an individual socket, if supported by the OS).
        </li>
<li class="listitem">
          Reactor-based <code class="computeroutput">io_service</code> implementations now use lazy initialisation
          to reduce the memory usage of an <code class="computeroutput">io_service</code> object used only
          as a message queue.
        </li>
</ul></div>
<h4>
<a name="asio.history.h37"></a>
      <span><a name="asio.history.asio_1_2_0"></a></span><a class="link" href="history.html#asio.history.asio_1_2_0">Asio
      1.2.0</a>
    </h4>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
          Added support for serial ports.
        </li>
<li class="listitem">
          Added support for UNIX domain sockets.
        </li>
<li class="listitem">
          Added support for raw sockets and ICMP.
        </li>
<li class="listitem">
          Added wrappers for POSIX stream-oriented file descriptors (excluding regular
          files).
        </li>
<li class="listitem">
          Added wrappers for Windows stream-oriented <code class="computeroutput">HANDLE</code>s such as
          named pipes (requires <code class="computeroutput">HANDLE</code>s that work with I/O completion
          ports).
        </li>
<li class="listitem">
          Added wrappers for Windows random-access <code class="computeroutput">HANDLE</code>s such as files
          (requires <code class="computeroutput">HANDLE</code>s that work with I/O completion ports).
        </li>
<li class="listitem">
          Added support for reactor-style operations (i.e. they report readiness
          but perform no I/O) using a new <code class="computeroutput">null_buffers</code> type.
        </li>
<li class="listitem">
          Added an iterator type for bytewise traversal of buffer sequences.
        </li>
<li class="listitem">
          Added new <code class="computeroutput">read_until()</code> and <code class="computeroutput">async_read_until()</code>
          overloads that take a user-defined function object for locating message
          boundaries.
        </li>
<li class="listitem">
          Added an experimental two-lock queue (enabled by defining <code class="computeroutput">(BOOST_)ASIO_ENABLE_TWO_LOCK_QUEUE</code>)
          that may provide better <code class="computeroutput">io_service</code> scalability across many
          processors.
        </li>
<li class="listitem">
          Various fixes, performance improvements, and more complete coverage of
          the custom memory allocation support.
        </li>
</ul></div>
<h4>
<a name="asio.history.h38"></a>
      <span><a name="asio.history.asio_1_0_0"></a></span><a class="link" href="history.html#asio.history.asio_1_0_0">Asio
      1.0.0</a>
    </h4>
<p>
      First stable release of Asio.
    </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M.
      Kohlhoff<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
      </p>
</div></td>
</tr></table>
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