handler_allocator.hpp
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//
// handler_allocator.cpp
// ~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#ifndef HANDLER_ALLOCATOR_HPP
#define HANDLER_ALLOCATOR_HPP
#include "asio.hpp"
#include <boost/aligned_storage.hpp>
#include <boost/noncopyable.hpp>
// Class to manage the memory to be used for handler-based custom allocation.
// It contains a single block of memory which may be returned for allocation
// requests. If the memory is in use when an allocation request is made, the
// allocator delegates allocation to the global heap.
class handler_allocator
: private boost::noncopyable
{
public:
handler_allocator()
: in_use_(false)
{
}
void* allocate(std::size_t size)
{
if (!in_use_ && size < storage_.size)
{
in_use_ = true;
return storage_.address();
}
return ::operator new(size);
}
void deallocate(void* pointer)
{
if (pointer == storage_.address())
{
in_use_ = false;
}
else
{
::operator delete(pointer);
}
}
private:
// Storage space used for handler-based custom memory allocation.
boost::aligned_storage<1024> storage_;
// Whether the handler-based custom allocation storage has been used.
bool in_use_;
};
// Wrapper class template for handler objects to allow handler memory
// allocation to be customised. Calls to operator() are forwarded to the
// encapsulated handler.
template <typename Handler>
class custom_alloc_handler
{
public:
custom_alloc_handler(handler_allocator& a, Handler h)
: allocator_(a),
handler_(h)
{
}
template <typename Arg1>
void operator()(Arg1 arg1)
{
handler_(arg1);
}
template <typename Arg1, typename Arg2>
void operator()(Arg1 arg1, Arg2 arg2)
{
handler_(arg1, arg2);
}
friend void* asio_handler_allocate(std::size_t size,
custom_alloc_handler<Handler>* this_handler)
{
return this_handler->allocator_.allocate(size);
}
friend void asio_handler_deallocate(void* pointer, std::size_t /*size*/,
custom_alloc_handler<Handler>* this_handler)
{
this_handler->allocator_.deallocate(pointer);
}
private:
handler_allocator& allocator_;
Handler handler_;
};
// Helper function to wrap a handler object to add custom allocation.
template <typename Handler>
inline custom_alloc_handler<Handler> make_custom_alloc_handler(
handler_allocator& a, Handler h)
{
return custom_alloc_handler<Handler>(a, h);
}
#endif // HANDLER_ALLOCATOR_HPP