c - 为什么 pthread_join() 从未被调用？

Question

我对 C 语言的多线程非常缺乏经验，因此我非常感谢对这段客户端代码的一些输入(为了简单起见，无关的部分已被删除)。

// client_read(): read from server
void *client_read(int sockfd) {
    char text[MAX_TEXT_SIZE + 2];
    while (1) {
        // clean out buffer
        bzero(text, sizeof(text));
        // read from server
        if (read(sockfd, text, sizeof(text)) <= 0) {
            fprintf(stderr, "failed to read\n");
            exit(1);
        }
        // print message from server to stdout
        fprintf(stdout, "%s", text);
        // quit conversation
        if (strncmp(text, "bye\n", 4) == 0) {
            fprintf(stdout, "end to conversation\n");
            close(sockfd);
            exit(0);
        }
    }
}

// client_write(): write to server
void *client_write(int sockfd) {
    char text[MAX_TEXT_SIZE + 2];
    int c, d, i;
    size_t text_len;
    while (1) {
        // clean out buffer
        bzero(text, sizeof(text));
        i = 0;
        // read from stdin
        while ((c = getchar()) != '\n' && c != EOF && i < MAX_TEXT_SIZE) {
            text[i++] = c;
        }
        // clean out stdin if MAX_TEXT_SIZE exceeded
        if (i == MAX_TEXT_SIZE && c != '\n') {
            while ((d = getchar()) != EOF && d != '\n') {
    }
        }
        text[i++] = '\n';
        text[i] = '\0';
        text_len = strlen(text);
        // write to server
        if (write(sockfd, text, text_len) != text_len) {
            fprintf(stderr, "sent wrong number of bytes\n");
            exit(1);
         }
        // quit conversation
        if (strncmp(text, "bye\n", 4) == 0) {
            fprintf(stdout, "end to conversation\n");
            close(sockfd);
            exit(0);
        }
    }
}

int main(int argc, char **argv) {
    char keyword[MAX_KEY_SIZE + 1], *server_IP;
    in_port_t server_port = 6000;
    int r_val, rtn_val, sockfd, w_val;
    pthread_t th_r, th_w;
    struct sockaddr_in server_addr;

    // checking number of command line arguments
    if (argc != 3 && argc != 5) {
        fprintf(stderr, "Usage: ./client server_IP [-p server_port] key\n");
        exit(1);
    }
    // Usage: ./client server_IP key
    else if (argc == 3) {
        if (strlen(argv[2]) > MAX_KEY_SIZE) {
            fprintf(stderr, "maximum key length exceeded\n");
            exit(1);
        }
        else {
            strcpy(keyword, argv[2]);
        }
    }
    // Usage: ./client server_IP -p server_port key
    else {
        if (strcmp("-p", argv[2]) != 0) {
            fprintf(stderr, "client: illegal option %s\n", argv[2]);
            exit(1);
        }
        else {
            server_port = atoi(argv[3]);
        }
        if (strlen(argv[4]) > MAX_KEY_SIZE) {
            fprintf(stderr, "maximum key length exceeded\n");
            exit(1);
        }
        else {
            strcpy(keyword, argv[4]);
        }
    }
    server_IP = argv[1];
    // creating reliable stream socket using TCP
    if ((sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
        fprintf(stderr, "unable to create TCP socket\n");
        exit(1);
    }
    // Constructing server address structure
    memset(&server_addr, 0, sizeof(server_addr));
    server_addr.sin_family = AF_INET;
    // Converting address into proper format
    if ((rtn_val = inet_pton(AF_INET, server_IP, &server_addr.sin_addr.s_addr)) == 0) {
        fprintf(stderr, "invalid IP address\n");
        exit(1);
    }
    else if (rtn_val < 0) {
        fprintf(stderr, "failed to convert IP string\n");
        exit(1);
    }
    // server port
    server_addr.sin_port = htons(server_port);
    // connecting to server
    if (connect(sockfd, (struct sockaddr *) &server_addr, sizeof(server_addr)) < 0) {
        fprintf(stderr, "failed to connect to server\n");
        exit(1);
    }
    // beginning chat
    else {
        fprintf(stdout, "successfully connected to server\n");
        // starting separate thread for reading from server
        if ((r_val = pthread_create(&th_r, NULL, (void *) client_read, (void *) sockfd)) != 0) {
            fprintf(stderr, "failed to create read thread\n");
            exit(1);
        }
        // starting separate thread for writing to server
        if ((w_val = pthread_create(&th_w, NULL, (void *) client_write, (void *) sockfd)) != 0) {
            fprintf(stderr, "failed to create write thread\n");
            exit(1);
        }
        // Waiting until threads close to return resources
        printf("hello1\n");
        pthread_join(th_r, NULL);
        printf("hello2\n");
        pthread_join(th_w, NULL);
        printf("hello3\n");
    }
    return 0;
}

对于熟悉客户端-服务器编程的人来说，您应该会发现，除了使用 POSIX 线程之外，客户端代码在处理用户输入以及读取和写入服务器方面没有任何异常。我决定使用单独的线程进行读取和写入；否则，客户端必须写一些东西，等待服务器回复，然后再写一些东西。

我在 main() 的最后使用了 pthread_join() 方法。这些函数应该等到读(th_r)和写(th_w)线程完成并放弃它们使用的资源。我遇到的问题是这些方法显然从未被调用过。

当我启动客户端时，我看到它立即到达“hello1”，但是当客户端或服务器终止通信流时，我看不到“hello2”或“hello3”，这意味着两者都没有到达。

有人可以解释一下我所缺少的内容吗？

Answer 1

您不应该在线程中调用 exit，您应该在线程完成时返回 NULL。调用 exit 只是终止整个程序。