pthread_exit() is reached before pthread_join call

Question

Having this piece of code:

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

void* PrintHello(void* data){

        printf("Hello from new thread\n");
        pthread_exit(NULL);

}

int main(int argc, char* argv[]){
    int rc;
    pthread_t thread_id;
    T_DATA data;

    Data = init_data();
    rc = pthread_create(&thread_id, NULL, PrintHello, (void*)data);
    if(rc){
        printf("\n ERROR: return code from pthread_create is %d \n", rc);
        exit(1);
    }
    sleep(100);
    printf("\n Created new thread (%d) ... \n", thread_id);
    pthread_join(thread_id);
}

When main creates the new thread and then perform sleep(100), the new thread probably reach pthread_exit before main reach pthread_join. Anyways the new thread waits and his resources are not freed until main perform pthread_join so if i execute ps command i will see the new thread during next 100 seconds, am i right?. I would get the same behavior if I use pthread_detach instead pthread_join? I wonder what happen when the new thread perform the pthread_exit before main perform pthread_detach over the thread.

Answer 1

The thread cannot be cleaned up until it terminates, of course. But it also cannot be cleaned up until it is either joined or detached. A thread that terminates without being detached will keep enough information around to allow another thread to join it.