为什么这个简单的Boost :: asio程序不能按预期工作？

Question

我写了这个:

#include <vector>
#include <iostream>
#include <sstream>
#include <boost/asio.hpp>
#include <tr1/memory>
#include <boost/bind.hpp>
#include <stdint.h>

    using namespace boost::asio;
    using namespace boost::asio::ip;

class tcpServer{
public:

    class connection{

        tcp::socket socketConnection;

        enum {CONNECTED, CLOSED, CREATED}STATUS;

    public:

        uint32_t addr;
        uint16_t port;

        connection(boost::asio::io_service &ioServ): socketConnection(ioServ){
            STATUS = CREATED;
        }

        void setConnected(bool is) {
            if (is) {
                STATUS = CONNECTED;
                port = socketConnection.remote_endpoint().port();
                addr
                        = socketConnection.remote_endpoint().address().to_v4().to_ulong();
                std::cout << "Connected to "
                        << socketConnection.remote_endpoint().address().to_v4().to_string()
                        << " : " << socketConnection.remote_endpoint().port()
                        << "\n";
            }
        }

        tcp::socket& getSocket(){
            return socketConnection;
        }
    };

    typedef std::tr1::shared_ptr<tcpServer::connection> CONNSHPTR;

private:
    boost::asio::io_service io_service;
    tcp::acceptor tcpAcceptor;
    int localPort;

    void accept(CONNSHPTR connection, const boost::system::error_code& error){
        connection->setConnected(true);
        std::cout.flush();
    }

    void startAccept(){
        CONNSHPTR newConn(new connection(tcpAcceptor.io_service()));

        tcpAcceptor.async_accept(newConn->getSocket(), boost::bind(
                        &tcpServer::accept, this, newConn,
                        boost::asio::placeholders::error));
    }

public:



    tcpServer(int localPort) :
        io_service(), tcpAcceptor(io_service, tcp::endpoint(tcp::v4(),
                localPort)) {
        this->localPort = localPort;

    }

    void start(){
        io_service.run();
        startAccept();
    }
};

int main(int argc, char** argv) {
try{
    tcpServer tp(1033);
    tp.start();
}catch(std::exception &e){
    std::cout << e.what();
}
    sleep(5000);
    return 0;
}

然后我去了终端,我写了telnet localhost 1033.Telnet说我已连接,但处理程序没有被调用(gdb没有命中断点,coutS没有效果).如果我杀了程序,telnet会说连接已经关闭.所以似乎连接已经建立,但为什么处理程序不被调用？

编辑:

奇怪的是,如果在start()中我将ioservice.run()放在startAccept()之后.现在我想知道为什么这个有用......事实上后来我再次调用start accept它仍然有效,它是在ioservice.run()调用之后....

Answer 1

来自asio文档:

run()函数将阻塞,直到所有工作完成,并且不再有调度程序,或者直到io_service已停止.

当在 startAccept()之前调用run()时,它会立即返回,因为它还没有任何操作.然后调用startAccept(),它将套接字置于接受模式(因此,当您在服务器上telnet时,网络子系统接受它),但之后不调用run(),因此永远不会调用您的接受处理程序.