c++ - c++11后台运行线程

Question

我有一个带有 connect_to 方法的类，我在其中启动了一个线程，在调用它并加入它之后，我希望该线程在后台运行并且程序会继续执行，但它卡在我的 connect_to 方法，直到线程执行停止。我记得我曾经在 C# 中使用线程，一旦我启动它们，它们就会在后台运行。

#ifndef _TCP_CLIENT_H_
#define _TCP_CLIENT_H_

#ifndef WIN32_LEAN_AND_MEAN
#define WIN32_LEAN_AND_MEAN
#endif

void connection_thread(void *user);


class TCPClient
{

public:
    SOCKET                m_ConnectSocket = INVALID_SOCKET;
    char                  m_recvbuf[BUFFER_LENGTH];
    int                   m_recvbuflen = BUFFER_LENGTH;
    struct addrinfo*      m_result = NULL, *m_ptr = NULL, m_hints;
    vector<PacketInfo*>   m_packet_list;
    PacketInfo*           m_packet_data = new PacketInfo();
    thread*               m_conn_thread;

    int state = 0;
    char* ip_address;
    unsigned int port = 0;

    TCPClient() {}
    ~TCPClient() {
        delete m_packet_data;
    }


    int Init_Sockets() {
        WSADATA wsaData;
        int iResult;

        iResult = WSAStartup(MAKEWORD(2, 2), &wsaData);
        if (iResult != 0) {
            printf("WSAStartup failed with error: %d\n", iResult);
            return 0;
        }
        return 1;
    }



    int Connect_to(char* ip, unsigned int port_number) {
        port = port_number;
        ip_address = ip;

        //thread conn_thread(connection_thread, this);
                thread conn_thread([=]() {connection_thread(this); return 1; });
        conn_thread.join();



        state = 0;
        return 1;
    }


}; // end TCPClient class




void connection_thread(void *user) {
    TCPClient * self = static_cast<TCPClient*>(user);


        // connecting code here... //


    self->state = CONNECTED;
    do {

        iResult = recv(self->m_ConnectSocket, self->m_recvbuf, self->m_recvbuflen, 0);
        if (iResult > 0) {
            printf("Bytes received: %d\n", iResult);
        }
        else if (iResult == 0) {
            printf("Connection closed\n");
            self->state = DISCONNECTED;
        }
        else {
            //printf("recv failed with error: %d\n", WSAGetLastError());
        }

    }
    while (iResult > 0);
}

#endif

线程按预期工作，并一直循环直到连接关闭。知道我错过了什么吗？

Answer 1

I have a class with a connect_to method which i'm starting a thread in it, after calling it and joining it, i expected the thread to run in the background and the program execution would continue but it hangs in my connect_to method until the thread execution stops

从字面上看，这就是加入线程应该做的!

如果您不想加入线程，那就干脆不要。 :)

不过，也许您至少应该在您的类析构函数中或稍后的某个时间执行此操作，这样您的主线程就不会在工作线程仍在执行时尝试结束。因为那将以泪水告终......

在我看来，这是一个完美的例子，说明为什么我们不应该在不理解原因的情况下编写代码行。 :) 您对 conn_thread.join() 的含义做出了一个假设，这个假设是错误的:在这种情况下首先要做的事情之一是阅读文档 以确保您的假设成立。理想情况下，您应该在编写代码之前阅读它，但没关系。