Threads stopped after function return

Question

I'm trying to create several thread workers in a function called engine_setup, but every time the function returns, every thread stops as well. I tried to create pthread id as global pointer but didn't help. here's the global:pthread_t * threadIDs; the engine_setup function:

query_helper* engine_setup(size_t n_processors) {
    //some code that is not relevant
    int err;
    threadIDs=malloc(n_processors*sizeof(*threadIDs));
    for(int i=0;i<n_processors;i++){
      err = pthread_create(&threadIDs[i],NULL,tp,(void*)helper);
      if (err != 0)
      printf("can't create thread \n");
    }
    printf("end setup\n");
    return helper;
}

and the thread function pointer is here:

void* tp(void * ptr){
    query_helper * helper=(query_helper*)ptr;
    while(1){
        printf("1\n");
    }
}

the output is something like this:

1
1
1
1
1
1
1
1
1
end setup

which shows that all the threads stopped when engine_setup return. Is there a way to keep them running?

Answer 1

Yes, you can call pthread_join(threadIds[i],null); (for all threads i), which will wait until the thred function returns.

You can use the second argument for storing return value from thread. I.e:

void *results[n_processors];
for(int i=0; i<n_processors; i++){
    pthread_join(threadIds[i], &results[i]);
}