c++ - boost::asio 是否进行过多的小堆分配或者我错了吗？

Question

#include <cstdlib>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/asio.hpp>

using boost::asio::ip::tcp;

class 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_, max_length - 1),
            boost::bind(&session::handle_read, 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)
        {
            data_[bytes_transferred] = '\0';
            if(NULL != strstr(data_, "quit"))
            {
                this->socket().shutdown(boost::asio::ip::tcp::socket::shutdown_both);
                this->socket().close(); // how to make this dispatch "handle_read()" with a "disconnected" flag?
            }
            else
            {
                boost::asio::async_write(socket_,
                    boost::asio::buffer(data_, bytes_transferred),
                    boost::bind(&session::handle_write, this,
                    boost::asio::placeholders::error));

                socket_.async_read_some(boost::asio::buffer(data_, max_length - 1),
                    boost::bind(&session::handle_read, this,
                    boost::asio::placeholders::error,
                    boost::asio::placeholders::bytes_transferred));
            }
        }
        else
        {
            delete this;
        }
    }

    void handle_write(const boost::system::error_code& error)
    {
        if (!error)
        {
            //
        }
        else
        {
            delete this;
        }
    }

private:
    tcp::socket socket_;
    enum { max_length = 1024 };
    char data_[max_length];
};

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* 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* new_session,
        const boost::system::error_code& error)
    {
        if (!error)
        {
            new_session->start();
            new_session = new session(io_service_);
            acceptor_.async_accept(new_session->socket(),
                boost::bind(&server::handle_accept, this, new_session,
                boost::asio::placeholders::error));
        }
        else
        {
            delete new_session;
        }
    }

private:
    boost::asio::io_service& io_service_;
    tcp::acceptor acceptor_;
};

int main(int argc, char* argv[])
{
    try
    {
        if (argc != 2)
        {
            std::cerr << "Usage: async_tcp_echo_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;
}

在试验 boost::asio 时，我注意到在对 async_write()/async_read_some() 的调用中使用了 C++“new”关键字。

此外，当使用客户端(1 个连接)发送例如 100,000 次某些数据时向此回显服务器施加压力时，此程序的内存使用量越来越高。

这是怎么回事？它会为每个调用分配内存吗？还是我错了？询问是因为服务器应用程序分配任何东西似乎都不对。我可以用内存池来处理吗？

另一个附带问题:

参见“this->socket().close();” ?
正如它的评论所说，我希望它最后一次分派(dispatch)相同的功能，但出现断开连接错误。需要做一些清理工作。我该怎么做？

谢谢各位大师(:

Answer 1

希望有人能有所贡献...

进一步在我在 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"new"代码处放置一个断点，即在“new.cpp”@function“void”处*__CRTDECL operator new(size_t size) _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 已开启，我正在连接一个客户端。
分配已完成(多次)(如预期)(我知道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。
来源是对 async_write() 的调用(我使用 MSVC 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产生对“new”的调用 !!!!!!真实服务器可能遇到的最坏情况!

因此，进一步寻找某种方法来使用某种内存池，这样这些"new"调用将不存在，这让我想到了示例:“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；
对 async_write() 和 async_read_some() 的调用不会生成对“new”的调用。

到目前为止还不错，但老实说我不能说我完全理解这是如何完成的；如您所见，分配器被分解成几个部分，这让我有点困惑。

make_custom_alloc_handler() <--- 它到底做了什么？
什么是 shared_from_this()？
我看到“ session ”对象有成员“handler_allocator allocator_”。每个“ session ”对象是否都包含这些对象的池？!我可以在将共享的“服务器”类级别拥有其中之一吗？

“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;
}