Question

How does a thread knows when to exit?

SITUATION:

-while the main program must wait for the threads to run to completion.

-This can be done by using a prototype function called pthread_join.

-after all, a call to this function waits for the termination of the thread whose id is given by thread itself.

Answer 1

After you have called pthread_join(ptherad_t &var)the main will wait untill all the threads for which you have called join have exited.

once all the threads are completed their tasks,
when it calls pthread_exit(NULL) main will exit.

inside the thread after its task is completed you need to call pthread_exit(NULL) which will stop the excution of the thread.But this is not mandatory and the thread can simply return which means that the thread has completed.

when it(thread) calls pthread_exit(NULL),the calling thread will exit.