希望有人能贡献一些东西......
进一步在 boost::asio 的实验中，我决定在服务器应用程序启动并运行后，我将在 C++ 的“新”代码处放置一个断点，即在“new.cpp”@ function“void *__CRTDECL 运算符”新的（size_t大小）_THROW1（_STD bad_alloc）”。请注意，我使用的是 MSVC 2008。
使用上面的原始帖子的代码:
现在 BP 已打开，我正在连接一个客户端。
分配已完成（几次）（如预期）（我知道这一点是因为调试器在我设置的“new”关键字处停止）并且新客户端现在已准备好发送/接收数据。
我从客户端向服务器发送“hi”。
'new'处的BP在handle_read()处被命中。
其来源是对 async_write() 的调用（我使用 MSVC 进行堆栈跟踪）。
按 F5（继续）会在“new”处生成另一个断点 - 这次是 async_read_some() 调用生成的。
结论：每个这样的操作都会生成对“new”的调用!!!!!!真实服务器可能出现的最坏情况！
因此，进一步寻找某种方法来使用某种内存池，这样这些“新”调用就不会存在，这让我想到了这个例子：“分配”。
它的路径：“......\boost_1_43_0\libs\asio\example\allocation\”。
对这个新代码（写在下面）做同样的事情给了我欢呼的结果;
调用 async_write() 和 async_read_some()不生成对“新”的呼唤。
到目前为止，一切都很好，但说实话，我不能说我完全理解这是如何完成的；如您所见，分配器被分解为几个部分，这让我有点困惑。
make_custom_alloc_handler() 什么是shared_from_this()？
我看到“会话”对象具有成员“handler_allocator allocator_”。每个“会话”对象是否都拥有这些对象的池？！我可以在“服务器”类级别拥有其中之一吗？它将被共享或其他什么？
“分配器”示例代码：
//
// server.cpp
// ~~~~~~~~~~
//
// Copyright (c) 2003-2010 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)
//
#include <cstdlib>
#include <iostream>
#include <boost/aligned_storage.hpp>
#include <boost/array.hpp>
#include <boost/bind.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/noncopyable.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/asio.hpp>
using boost::asio::ip::tcp;
// 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();
}
else
{
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);
}
class session
: public boost::enable_shared_from_this<session>
{
public:
session(boost::asio::io_service& io_service)
: socket_(io_service)
{
}
tcp::socket& socket()
{
return socket_;
}
void start()
{
socket_.async_read_some(boost::asio::buffer(data_),
make_custom_alloc_handler(allocator_,
boost::bind(&session::handle_read,
shared_from_this(),
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred)));
}
void handle_read(const boost::system::error_code& error,
size_t bytes_transferred)
{
if (!error)
{
boost::asio::async_write(socket_,
boost::asio::buffer(data_, bytes_transferred),
make_custom_alloc_handler(allocator_, boost::bind(&session::handle_write, shared_from_this(), boost::asio::placeholders::error))
);
}
}
void handle_write(const boost::system::error_code& error)
{
if (!error)
{
socket_.async_read_some(boost::asio::buffer(data_),
make_custom_alloc_handler(allocator_,
boost::bind(&session::handle_read,
shared_from_this(),
boost::asio::placeholders::error,
boost::asio::placeholders::bytes_transferred)));
}
}
private:
// The socket used to communicate with the client.
tcp::socket socket_;
// Buffer used to store data received from the client.
boost::array<char, 1024> data_;
// The allocator to use for handler-based custom memory allocation.
handler_allocator allocator_;
};
typedef boost::shared_ptr<session> session_ptr;
class server
{
public:
server(boost::asio::io_service& io_service, short port)
: io_service_(io_service),
acceptor_(io_service, tcp::endpoint(tcp::v4(), port))
{
session_ptr new_session(new session(io_service_));
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
void handle_accept(session_ptr new_session,
const boost::system::error_code& error)
{
if (!error)
{
new_session->start();
new_session.reset(new session(io_service_));
acceptor_.async_accept(new_session->socket(),
boost::bind(&server::handle_accept, this, new_session,
boost::asio::placeholders::error));
}
}
private:
boost::asio::io_service& io_service_;
tcp::acceptor acceptor_;
};
int main(int argc, char* argv[])
{
try
{
if (argc != 2)
{
std::cerr << "Usage: server <port>\n";
return 1;
}
boost::asio::io_service io_service;
using namespace std; // For atoi.
server s(io_service, atoi(argv[1]));
io_service.run();
}
catch (std::exception& e)
{
std::cerr << "Exception: " << e.what() << "\n";
}
return 0;
}
