Thread Termination

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Terminating Threads.

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There are several ways in which a Pthread may be terminated:

a

The thread returns from its starting routine (the main routine for the initial thread).

b

The thread makes a call to the pthread_exit subroutine.

• Typically, the pthread_exit routine is called after a thread has completed its work and is no longer required to exist.

c

The thread is cancelled by another thread via the pthread_cancel routine.

d

The entire process is terminated due to a call to either the exec or exit subroutines.

• If main finishes before the threads and exits with pthread_exit(), the other threads will continue to execute (join function).
• If main finishes after the threads and exits, the threads will be automatically terminated.

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Cleanup: the pthread_exit() routine does not close files; any files opened inside the thread will remain open after the thread is terminated.

• Example: This example code creates 5 threads with the pthread_create() routine.
• Each thread prints a 'Hello World!' message, and then terminates with a call to pthread_exit().

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS     5

void *PrintHello(void *threadid)
{
  long tid;
  tid = (long)threadid;
  printf("Hello World! It's me, thread #%ld!\n", tid);
  pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
  pthread_t threads[NUM_THREADS];
  int rc;
  long t;
  for(t=0; t<NUM_THREADS; t++){
    printf("In main: creating thread %ld\n", t);
    rc = pthread_create(&threads[t], NULL, PrintHello, 
                                                  (void *)t);
    if (rc){
      printf("ERROR; return code from pthread_create() is
                                                  %d\n", rc);
      exit(-1);
    }
  }
pthread_exit(NULL);
}