Cpp socket - TCP传输（用同一端口发送然后接收）

Question

我正在写套接字编程，一部分先发送然后接收，一部分是接收然后发送。

的工作方案是这样的：

的ThreadA：发送到端口8000->关闭套接字 - >获得MyPort上（门），我送 - >听我的端口（门）

ThreadB ：监听端口8000 - >获取该端口接收（门） - >关闭套接字 - >送包到同一个端口（端口A）

std::thread ThreadA,ThreadB; 
long share_port=8000; 
char share_addr[INET_ADDRSTRLEN]="127.0.0.1"; 

void send_then_receive(); 
void receive_then_send(); 


void send_then_receive(){ 
    long myport = -1, receiver_port = share_port; 
    SOCKET receive_then_send_A_Socket,receive_then_send_A_Socket_b,receive_then_send_B_Socket; 

    //- Send to who i want 
    struct sockaddr_in receive_then_send_B_Addr; 
    receive_then_send_B_Addr.sin_family = AF_INET; 
    inet_pton(AF_INET, share_addr, &receive_then_send_B_Addr.sin_addr.s_addr); 
    receive_then_send_B_Addr.sin_port = htons((u_short)receiver_port); 
    receive_then_send_B_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); 
    while (connect(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, sizeof(sockaddr_in)) == SOCKET_ERROR){ 
     printf("\nConnect Fail in first response| Fail Code:%i\n", WSAGetLastError()); 
    } 
    send(receive_then_send_B_Socket, "4321", 5, 0); 
    printf("[1]The port I want to send to:%ld\n",receiver_port); 

    //- Check My Port 
    socklen_t checkport_adr_len = sizeof(receive_then_send_B_Addr); 
    if (getsockname(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, &checkport_adr_len) == 0){ 
     myport = ntohs(receive_then_send_B_Addr.sin_port); 
     printf("[1]MyPort Check:%ld\n", myport); 
    } 
    close(receive_then_send_B_Socket); 



    //- Then Recive 
    sockaddr_in *receive_then_send_A_Addr = new sockaddr_in; 
    receive_then_send_A_Addr->sin_family = AF_INET; 
    receive_then_send_A_Addr->sin_addr.s_addr = INADDR_ANY; 
    receive_then_send_A_Addr->sin_port = htons((u_short)myport); 
    receive_then_send_A_Socket = socket(AF_INET, SOCK_STREAM, 0); 
    bind(receive_then_send_A_Socket, (struct sockaddr *)receive_then_send_A_Addr, sizeof(struct sockaddr_in)); 
    listen(receive_then_send_A_Socket, 1); 
    std::this_thread::sleep_for(std::chrono::milliseconds(1000)); 
    receive_then_send_A_Socket_b = accept(receive_then_send_A_Socket, 0, 0); 
    char* buffer_A= new char[100]; 
    recv(receive_then_send_A_Socket_b, buffer_A, 100, 0); 
    printf("[1]What I then receive: %s\n",buffer_A); 

    close(receive_then_send_A_Socket); 
    close(receive_then_send_A_Socket_b); 


} 
void receive_then_send(){ 
    long myport = -1, receiver_port = -1; 
    SOCKET receive_then_send_A_Socket,receive_then_send_A_Socket_b,receive_then_send_B_Socket; 

    //- First Recive 
    sockaddr_in *receive_then_send_A_Addr = new sockaddr_in; 
    receive_then_send_A_Addr->sin_family = AF_INET; 
    receive_then_send_A_Addr->sin_addr.s_addr = INADDR_ANY; 
    receive_then_send_A_Addr->sin_port = htons((u_short)share_port); 
    receive_then_send_A_Socket = socket(AF_INET, SOCK_STREAM, 0); 
    bind(receive_then_send_A_Socket, (struct sockaddr *)receive_then_send_A_Addr, sizeof(struct sockaddr_in)); 
    listen(receive_then_send_A_Socket, 1); 
    receive_then_send_A_Socket_b = accept(receive_then_send_A_Socket, 0, 0); 
    char* buffer_A= new char[100]; 
    recv(receive_then_send_A_Socket_b, buffer_A, 100, 0); 
    printf("[2]What I first receive: %s\n",buffer_A); 

    //- Check receiver Port 
    struct sockaddr_storage receiver_addr; 
    socklen_t receiver_addr_len = (socklen_t)sizeof receiver_addr; 
    getpeername(receive_then_send_A_Socket_b, (struct sockaddr*)&receiver_addr, &receiver_addr_len); 


    struct sockaddr_in *s = (struct sockaddr_in *)&receiver_addr; 
    inet_ntop(AF_INET, &s->sin_addr, share_addr, sizeof share_addr); 
    receiver_port = ntohs(s->sin_port); 
    printf("[2]The port I want to send to:%ld\n",receiver_port); 
    close(receive_then_send_A_Socket); 
    close(receive_then_send_A_Socket_b); 

    //- Send Back to the port that sender send to me 
    struct sockaddr_in receive_then_send_B_Addr; 
    receive_then_send_B_Addr.sin_family = AF_INET; 
    inet_pton(AF_INET, share_addr, &receive_then_send_B_Addr.sin_addr.s_addr); 
    receive_then_send_B_Addr.sin_port = htons((u_short)receiver_port); 
    receive_then_send_B_Socket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP); 
    while (connect(receive_then_send_B_Socket, (struct sockaddr *)&receive_then_send_B_Addr, sizeof(sockaddr_in)) == SOCKET_ERROR){ 
     printf("\nFail Code:%i\n", WSAGetLastError()); 
     break; 
    } 
    send(receive_then_send_B_Socket, "1234", 5, 0); 
    close(receive_then_send_B_Socket); 
    printf("[2]The port I want to send to:%ld\n",receiver_port); 
} 

int main(int argc, char *argv[]) 
{ 
    ThreadB = std::thread(receive_then_send); 
    ThreadA = std::thread(send_then_receive); 
    while(1); 
    return 0; 
} 

然而，它运作良好，在第一次传输，但它不工作在第二次传输，什么是错的？

它这样表示：

连接失败的第一反应|失败代码：111

Connect in Fail in first response |失败码：111 [1]我想 的端口发送至：8000 [1] MyPort上检查：34004 [2]我第一次收到4321 [2]我要发送到的端口：34004

失败代码：111

请注意：我使用Linux（第二次传输不起作用），但是当我修改为WinSock版本时，所有功能都很好。为什么会发生？

请注意，在绑定之前，我已经厌倦了 //将套接字上的SO_REUSEADDR设置为true（1）： int optval = 1; setsockopt（receive_then_send_A_Socket，SOL_SOCKET，SO_REUSEADDR，& optval，sizeof（int））;

Answer 1

One liner answer：SO_REUSEADDR。

系统禁止重复使用给定端口上的IP地址，我记得它在释放后60秒。除非SO_REUSEADDR标志已被设置。

这是一个comprehensive answer on SO关于为什么以及如何设置此选项标志。