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

Thanks all for the great answers! There has been a lot of talk about using memory barriers etc - so I figured I'd post an answer that properly showed them used for this.

#define NUM_THREADS 5

unsigned int thread_count;
void *threadfunc(void *arg) {
  printf("Thread %p running\n",arg);
  sleep(3);
  printf("Thread %p exiting\n",arg);
  __sync_fetch_and_sub(&thread_count,1);
  return 0L;
}

int main() {
  int i;
  pthread_t thread[NUM_THREADS];

  thread_count=NUM_THREADS;
  for (i=0;i

Note that the __sync macros are "non-standard" GCC internal macros. LLVM supports these too - but if your using another compiler, you may have to do something different.

Another big thing to note is: Why would you burn an entire core, or waste "half" of a CPU spinning in a tight poll-loop just waiting for others to finish - when you could easily put it to work? The following mod uses the initial thread to run one of the workers, then wait for the others to complete:

  thread_count=NUM_THREADS;
  for (i=1;i

Note that we start creating the threads starting at "1" instead of "0", then directly run "thread 0" inline, waiting for all threads to complete after it's done. We pass &thread[0] to it for consistency (even though it's meaningless here), though in reality you'd probably pass your own variables/context.