How can I wait for any/all pthreads to complete?

Question

I just want my main thread to wait for any and all my (p)threads to complete before exiting.

The threads come and go a lot for different reasons, and I really don\'

Answer 1

Do you want your main thread to do anything in particular after all the threads have completed?

If not, you can have your main thread simply call pthread_exit() instead of returning (or calling exit()).

If main() returns it implicitly calls (or behaves as if it called) exit(), which will terminate the process. However, if main() calls pthread_exit() instead of returning, that implicit call to exit() doesn't occur and the process won't immediately end - it'll end when all threads have terminated.

• http://pubs.opengroup.org/onlinepubs/007908799/xsh/pthread_exit.html

Can't get too much quick-n-dirtier.

Here's a small example program that will let you see the difference. Pass -DUSE_PTHREAD_EXIT to the compiler to see the process wait for all threads to finish. Compile without that macro defined to see the process stop threads in their tracks.

#include 
#include 
#include 
#include 

static
void sleep(int ms)
{
    struct timespec waittime;

    waittime.tv_sec = (ms / 1000);
    ms = ms % 1000;
    waittime.tv_nsec = ms * 1000 * 1000;

    nanosleep( &waittime, NULL);
}

void* threadfunc( void* c)
{
    int id = (int) c;
    int i = 0;

    for (i = 0 ; i < 12; ++i) {
        printf( "thread %d, iteration %d\n", id, i);
        sleep(10);
    }

    return 0;
}


int main()
{
    int i = 4;

    for (; i; --i) {
        pthread_t* tcb = malloc( sizeof(*tcb));

        pthread_create( tcb, NULL, threadfunc, (void*) i);
    }

    sleep(40);

#ifdef USE_PTHREAD_EXIT
    pthread_exit(0);
#endif

    return 0;
}