使用-lpthread在C中进行多线程

Question

So I designed a server to accept multiple clients in real time where the clients will 'speak' and the server will 'repeat' it. The clients will remain active constantly until I quit it. I tried implementing this using the -lpthread but the server will accept all the client connections, but then ignore all commands received except from the first client. Here is what I tried so far:

int main(int argc, char *argv[]) {
    pthread_t client_thread;
    pthread_attr_t attr;
... 
while(1) {  /* main accept() loop */


    sin_size = sizeof(struct sockaddr_in);
    if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, \
    &sin_size)) == -1) {
        perror("accept");
        continue;
    }
    printf("server: got connection from %s\n", \
        inet_ntoa(their_addr.sin_addr));

    pthread_attr_t attr;
    pthread_attr_init(&attr);

    for (int i = 0; i < MAX_CLIENTS; i++) {
        pthread_create(&client_thread, &attr, decider, new_fd);
        pthread_join(client_thread,NULL);
    }
...

Currently, the only options I can choose between are multithreading or thread pooling. Thanks.

Answer 1

You call pthread_create and then immediately pthread_join .

The problem with that is that pthread_join will wait for the thread to exit, making your code serial instead of parallel.

If you want to dynamically create a thread when you receive a connection, then create one thread. Don't create MAX_CLIENT threads in a loop, where all threads handle the very same connection.

---

If you want to use a thread-pool, then create all threads first before the "main accept() loop", and simply have them do nothing (to begin with). Then use a (protected) queue where you add new connections, and the threads check this queue for new connections, and the one thread that doesn't already handle a connection will pick it up and process it.

In pseudo-code, something like this:

thread_function()
{
    while (true)
    {
        sleep_while_queue_is_empty();
        get_descriptor_from_queue();

        handle_connection();
    }
}