c - 为什么 pthread_join 没有返回？

Question

我认为 pthread_join 应该总是返回一个值，然后让主线程处理之后的代码。根据我过去的经验，这会奏效。但现在我坚持下去了。不知何故，它只是不返回并阻塞主线程。或者它可能是执行任务的主线程。我不知道为什么。在下面的代码中，在终止客户端之前我无法到达“Thread created2”。有什么想法吗？

int main(int argc, char *argv[]) {

    int sockfd, port;  /* listen on sock_fd, new connection on new_fd */
    struct sockaddr_in my_addr;    /* my address information */
    struct sockaddr_in their_addr; /* connector's address information */
    socklen_t sin_size;

    if(signal(SIGINT, sigintEvent) == SIG_ERR)
        printf("can't catch SIGINT!");

    /* generate the socket */
    if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    if (argc > 1) {
        port = atoi(argv[1]);
    } else {
        port = MYPORT;
    }

    /* generate the end point */
    my_addr.sin_family = AF_INET;         /* host byte order */
    my_addr.sin_port = htons(port);     /* short, network byte order */
    my_addr.sin_addr.s_addr = INADDR_ANY; /* auto-fill with my IP */
    /* bzero(&(my_addr.sin_zero), 8);   ZJL*/     /* zero the rest of the struct */

    /* bind the socket to the end point */
    if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) \
            == -1) {
        perror("bind");
        exit(1);
    }

    /* start listnening */
    if (listen(sockfd, MAXCONNECTIONS) == -1) {
        perror("listen");
        exit(1);
    }

    createPool(MAXCONNECTIONS);

    /* create a node pointer as head of the list */
    head = (node*)malloc(sizeof(node));

    openFile();

    printf("server starts listnening ...\n");

    int new_fd;
    sin_size = sizeof(struct sockaddr_in);

    while((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size))) {
        printf("Accepted!\n");
        printf("server: got connection!\n");

        //tNode* tThread = (tNode*)threadDequeue();

        pthread_t pt;

        printf("Got tThread.\n");

        if((pthread_create(&pt, NULL, runService,(void*)&new_fd)) != 0) {
            printf("error creating thread.");
            abort();
        }

        printf("Thread created.\n");

        if( pthread_join(pt, NULL) != 0 ) {
            printf("error joining thread");
            abort();
        }

        printf("Thread created2.\n");
    }

    exit(1);
}

Answer 1

从文档中我们可以阅读以下关于 pthread_join 的信息

The pthread_join() function waits for the thread specified by thread to terminate. If that thread has already terminated, then pthread_join() returns immediately. The thread specified by thread must be joinable.

这表明在您的情况下，父线程正在等待其子线程pt 完成。正在执行 runService 的子线程 pt 仍未返回/完成。因此，您的父线程将继续等待完成(不从 pthread_join 方法返回)。

您应该尝试查看runService 的代码以了解这种情况。