c++ - 提升 asio 同步与异步操作性能

Question

这有点类似于boost::asio async performance .由于该问题没有确定的答案，我发布了一个类似的问题，其中包含示例代码和统计数据来证明该问题。

下面，我对同步和异步服务器应用程序进行了示例，它们在一个循环中连续向客户端发送 25 字节的消息。在客户端，我正在检查它能够以什么速率接收消息。示例设置非常简单。在同步服务器的情况下，它会为每个客户端连接生成一个新线程，并且该线程会循环发送 25 字节的消息。在异步服务器的情况下，它也会为每个客户端连接生成一个新线程，并且该线程使用异步写入在循环中不断发送 25 字节的消息(主线程是调用 ioservice.run()).对于性能测试，我只使用一个客户端。

同步服务器代码:

#include <iostream>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>
#include <boost/thread.hpp>

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

class tcp_connection : public boost::enable_shared_from_this<tcp_connection>
{
public:
    typedef boost::shared_ptr<tcp_connection> pointer;

    static pointer create(boost::asio::io_service& io_service)
    {
       return pointer(new tcp_connection(io_service));
    }

    tcp::socket& socket()
    {
        return socket_;
    }

    void start()
    {
        for (;;) {
            try {
                ssize_t len = boost::asio::write(socket_, boost::asio::buffer(message_));
                if (len != message_.length()) {
                    std::cerr<<"Unable to write all the bytes"<<std::endl;
                    break;
                }
                if (len == -1) {
                    std::cerr<<"Remote end closed the connection"<<std::endl;
                    break;
                }
            }
            catch (std::exception& e) {
                std::cerr<<"Error while sending data"<<std::endl;
                break;
            }
        }
    }

private:
    tcp_connection(boost::asio::io_service& io_service)
        : socket_(io_service),
          message_(25, 'A')
    {
    }

    tcp::socket socket_;
    std::string message_;
};

class tcp_server
{
public:
    tcp_server(boost::asio::io_service& io_service)
        : acceptor_(io_service, tcp::endpoint(tcp::v4(), 1234))
    {
        start_accept();
    }

private:
    void start_accept()
    {
        for (;;) {
            tcp_connection::pointer new_connection =
                tcp_connection::create(acceptor_.get_io_service());
            acceptor_.accept(new_connection->socket());
            boost::thread(boost::bind(&tcp_connection::start, new_connection));
        }
    }
    tcp::acceptor acceptor_;
};

int main()
{
    try {
        boost::asio::io_service io_service;
        tcp_server server(io_service);
    }
    catch (std::exception& e) {
        std::cerr << e.what() << std::endl;
    }
    return 0;
}

A同步服务器代码:

#include <iostream>
#include <string>
#include <boost/bind.hpp>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/asio.hpp>

#include <boost/thread.hpp>

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

class tcp_connection
        : public boost::enable_shared_from_this<tcp_connection>
{
public:
    typedef boost::shared_ptr<tcp_connection> pointer;

    static pointer create(boost::asio::io_service& io_service)
    {
        return pointer(new tcp_connection(io_service));
    }

    tcp::socket& socket()
    {
        return socket_;
    }

    void start()
    {
        while (socket_.is_open()) {
            boost::asio::async_write(socket_, boost::asio::buffer(message_),
                boost::bind(&tcp_connection::handle_write, shared_from_this(),
                            boost::asio::placeholders::error,
                            boost::asio::placeholders::bytes_transferred));
        }
    }

private:
    tcp_connection(boost::asio::io_service& io_service)
        : socket_(io_service),
          message_(25, 'A')
    {
    }

    void handle_write(const boost::system::error_code& error,
                      size_t bytes_transferred)
    {
        if (error) {
            if (socket_.is_open()) {
                std::cout<<"Error while sending data asynchronously"<<std::endl;
                socket_.close();
            }
        }
    }

    tcp::socket socket_;
    std::string message_;
};

class tcp_server
{
public:
    tcp_server(boost::asio::io_service& io_service)
        : acceptor_(io_service, tcp::endpoint(tcp::v4(), 1234))
    {
        start_accept();
    }

private:
    void start_accept()
    {
        tcp_connection::pointer new_connection =
                tcp_connection::create(acceptor_.get_io_service());
        acceptor_.async_accept(new_connection->socket(),
                boost::bind(&tcp_server::handle_accept, this, new_connection,
                        boost::asio::placeholders::error));
    }

    void handle_accept(tcp_connection::pointer new_connection,
                       const boost::system::error_code& error)
    {
        if (!error) {
            boost::thread(boost::bind(&tcp_connection::start, new_connection));
        }

        start_accept();
    }

    tcp::acceptor acceptor_;
};

int main()
{
    try {
        boost::asio::io_service io_service;
        tcp_server server(io_service);
        io_service.run();
    }
    catch (std::exception& e) {
        std::cerr << e.what() << std::endl;
    }

    return 0;
}

客户端代码:

#include <iostream>

#include <boost/asio.hpp>
#include <boost/array.hpp>

int main(int argc, char* argv[])
{
    if (argc != 3) {
        std::cerr<<"Usage: client <server-host> <server-port>"<<std::endl;
        return 1;
    }

    boost::asio::io_service io_service;
    boost::asio::ip::tcp::resolver resolver(io_service);
    boost::asio::ip::tcp::resolver::query query(argv[1], argv[2]);
    boost::asio::ip::tcp::resolver::iterator it = resolver.resolve(query);
    boost::asio::ip::tcp::resolver::iterator end;
    boost::asio::ip::tcp::socket socket(io_service);
    boost::asio::connect(socket, it);

//    Statscollector to periodically print received messages stats
//    sample::myboost::StatsCollector stats_collector(5);
//    sample::myboost::StatsCollectorScheduler statsScheduler(stats_collector);
//    statsScheduler.start();

    for (;;) {
        boost::array<char, 25> buf;
        boost::system::error_code error;
        size_t len = socket.read_some(boost::asio::buffer(buf), error);
//        size_t len = boost::asio::read(socket, boost::asio::buffer(buf));
        if (len != buf.size()) {
            std::cerr<<"Length is not "<< buf.size() << " but "<<len<<std::endl;
        }
//        stats_collector.incr_msgs_received();
    }
}

问题:

当客户端针对同步服务器运行时，它能够接收大约 700K 消息/秒，但当它针对异步服务器运行时，性能下降到大约 100K-120K 消息/秒。我知道当我们有更多客户端时应该使用异步 IO 来实现可伸缩性，在上述情况下，因为我只使用一个客户端，异步 IO 的明显优势并不明显。但问题是，对于单个客户端情况，异步 IO 是否会严重影响性能，或者我是否缺少一些明显的异步 IO 遵循的最佳实践？性能的显着下降是因为ioservice线程(在上面的例子中是主线程)和连接线程之间的线程切换吗？

设置: 我在 Linux 机器上使用 BOOST 1.47。

Answer 1

这不是异步发送的使用方式:以这种方式，连接的线程将越来越多的写入请求放入 asio 队列，同时线程调用 ioservice.run() 正在使它们出队。

低性能很可能是由于部分主线程(生产者)和运行 ioservice 的线程(消费者)上的 ioservice 工作队列存在高竞争。

此外，如果你监控你的内存，你应该看到它在增长，最终会阻塞你的系统:我确实希望生产者比消费者更快。

正确的方法(未经测试)，只报告两个相关的方法，应该是这样的:

    void start()
    {
        boost::asio::async_write(socket_, boost::asio::buffer(message_),
            boost::bind(&tcp_connection::handle_write, shared_from_this(),
                        boost::asio::placeholders::error,
                        boost::asio::placeholders::bytes_transferred));
    }

    void handle_write(const boost::system::error_code& error,
                      size_t bytes_transferred)
    {
        if (error) {
            if (socket_.is_open()) {
                std::cout<<"Error while sending data asynchronously"<<std::endl;
                socket_.close();
            }
        }
        if (socket_.is_open()) {
            boost::asio::async_write(socket_, boost::asio::buffer(message_),
                boost::bind(&tcp_connection::handle_write, shared_from_this(),
                            boost::asio::placeholders::error,
                            boost::asio::placeholders::bytes_transferred));
        }

    }    

也就是说，连接线程只“点燃”一个事件驱动循环，即运行ioservice线程的一部分:一旦写执行后，将调用回调以发布下一个。