CODEWITHSUNDEEP
cmultithreadingsockets
NewToAndroid
NewToAndroid

Reputation: 581

Listening thread does not print statements

I am doing socket programming in C. In essence, I need a server that runs the indefinite listening loop in a separate thread and whenever it accepts a new connection, it must create a new client thread to handle the client's requests.

Below I have the main function that declares a port number and calls the function createListenThread. This function creates a new thread and invokes the function listenLoop. 

int main(int argc, char *argv[])
{
    int client_port = 6000;
    createListenThread(client_port);
}

void createListenThread(int listen_port)
{   
    pthread_t listen_tid;

    printf("In createListenThread\n");  
    // listenLoop(&listen_port);

    if(pthread_create(&listen_tid, NULL, listenLoop, &listen_port) != 0)
        socketError("Could not create thread\n");       

}

void *listenLoop(void *arg)
{
    pthread_detach(pthread_self());

        int listen_socket, listen_port, *client_socket, struct_size;
    struct sockaddr_in client_addr; 
    pthread_t client_tid;

    listen_port = *((int *)arg);        
    listen_socket = createSocket(listen_port);
    struct_size = sizeof(struct sockaddr_in);

    while(1)
    {  
        printf("In ListenLoop\n");
            client_socket = malloc(sizeof(int));
            *client_socket = -1;
            *client_socket = accept(listen_socket, (struct sockaddr *)&client_addr, &struct_size);

            printf("Received connection request from (%s , %d)\n",
            inet_ntoa(client_addr.sin_addr),ntohs(client_addr.sin_port));

            pthread_create(&client_tid, NULL, starterFunction, client_socket);
    }

    close(listen_socket);
}

My problem is that whenever I run the server, only "In ListenThread" and "In ListenLoop" is never printed. I have even tried fprintf(stdout, "In ListenLoop") and fflush(stdout) but the statement is still not printed. When I comment out:

if(pthread_create(&listen_tid, NULL, listenLoop, &listen_port) != 0)
         socketError("Could not create thread\n");

and simply invoke ListenLoop as follows:

listenLoop(&listen_port);

Both the print statements appear. Is there an obvious mistake in the way I'm creating the thread and invoking the ListenLoop function? Is the function ListenLoop ever executed?

Edit: I ran the program in gdb which printed the following:

In createListenThread
[New Thread 0xb7e30b70 (LWP 10024)]   
[Thread 0xb7e30b70 (LWP 10024) exited]
[Inferior 1 (process 10021) exited normally]

Why is the thread exiting??

Upvotes: 0

Views: 196

Answers (2)

Serge Ballesta
Serge Ballesta

Reputation: 148890

I hope that you declare all your functions above main ... But you should really call your listenLoop in main thread. Else, you create a thread to run the loop and main thread passively waits it. And you will not be bothered by argument passing, thread waiting and so on.

listenLoop could then be a true void and no longer a void *, as you do not return anything.

If you were forking a process, it would make sense, since it is the correct way to create a daemon process immediateley adopted by init process, but for threads it is simply useless.

Upvotes: 0

mathematician1975
mathematician1975

Reputation: 21351

The problem will be that your main function returns immediately after calling createListenThread. You should wait for your thread function to finish using pthread_join within your createListenThread otherwise the program may terminate before the thread function can finish. Calling pthread_join on your thread will wait until the thread function returns and will therefore definitely get chance to run before main() returns.

Upvotes: 2

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