停止阻塞recv()的接收器线程

Question

我有一个聊天应用程序,它有一个单独的线程来监听传入的消息.

while (main thread not calling for receiver to quit) {
  string message = tcpCon.tcpReceive();    // Relies on the recv() function
  processIncomingMessage(message);
}

这种工作方式有一个大问题.大多数情况下,循环将被阻塞,recv()因此接收器线程将不会退出.在没有强制线程终止几秒钟的情况下解决此问题的正确方法是什么？

Answer 1

关闭插座,shutdown()关闭所有接收器.

这会在我的系统上输出'recv return 0',表示接收器看到有序关机.评论shutdown()并观看它永远挂起.

从长远来看,OP应该修复设计,使用select或包含协议中的显式退出消息.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <pthread.h>

/* Free on my system. YMMV */
int port = 7777;
int cd;

void *f(void *arg)
{
    /* Hack: proper code would synchronize here */
    sleep(1);

    /* This works: */
    shutdown(cd, SHUT_RDWR);

    close(cd);
    return 0;
}

int main(void)
{
    /* Create a fake server which sends nothing */
    int sd = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in sa = { 0 };
    const int on = 1;
    char buf;
    pthread_t thread;
    sa.sin_family = AF_INET;
    sa.sin_addr.s_addr = htonl(INADDR_ANY);
    sa.sin_port = htons(port);
    setsockopt(sd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof on);

    /* Other error reporting omitted for clarity */
    if (bind(sd, (const struct sockaddr*)&sa, sizeof sa) < 0) {
        perror("bind");
        return EXIT_FAILURE;
    }

    /* Create a client */
    listen(sd, 1);
    cd = socket(AF_INET, SOCK_STREAM, 0);
    connect(cd, (const struct sockaddr*)&sa, sizeof sa);
    accept(sd, 0, 0);

    /* Try to close socket on another thread */
    pthread_create(&thread, 0, f, 0);
    printf("recv returned %d\n", recv(cd, &buf, 1, 0));
    pthread_join(thread, 0);

    return 0;
}

Answer 2

您可以使用 select() 等待传入数据并避免在 receive() 中阻塞。select() 也会阻塞，但您可以让它在设定的时间间隔后超时，以便 while 循环可以继续并检查从主线程退出的信号：

while (main thread not calling for receiver to quit) {
  if (tcpCon.hasData(500)) {              // Relies on select() to determine that data is
                                          // available; times out after 500 milliseconds
    string message = tcpCon.tcpReceive(); // Relies on the recv() function
    processIncomingMessage(message);
  }
}