Thread: Can't get Mutual Exclusion to Work

I have a program that spawns a number of threads. Each thread generates a table of output. During the time that it is creating this output, I don't want the other threads to be outputting, so I've attempted to create a mutex semaphore to allow only one thread at time to ouput.

Code:

sem_t mutex;

void* node(void *thread_arg) {

    ...
    // set a mutex lock to allow the output for this next step to complete for this thread
    sem_wait(&mutex);

   // generate table with various fprintf statements

   sem_post(&mutex);

   ...
}

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

    // semaphore to allow the output to organize correctly
    sem_init(&mutex, 0, 1);
    
    // spawn a separate thread for each host
    for (i = 0; i < NUM_HOSTS; i++) {
        host_thread[i] = (pthread_t *) malloc(sizeof(pthread_t));
        
        if (verbose) printf ("In main, spawning thread for host %d\n", i);
        
        int rc = pthread_create (host_thread[i], NULL, node, (void *) &thread_data_array[i]);
        
        if (rc)
            printf("ERROR: return code from pthread_create() is %d for host thread %d\n", rc, i);
    }

    ...
}

This approach isn't working. Can anyone set me on the right path? Thanks!

Perfect. Easy solution. Exactly what I needed. Thank you!