Question

Possible Duplicate:
Understanding pthread_detach

The following code is creating a single thread which prints “new thread” .

#include<stdio.h>
#include<pthread.h>
void *thr_fn(void *arg)
{
      printf("New thread\n");
      sleep(5);
      return (void *)1;
}
int main()
{
       pthread_t pid;
       void *t;
       pthread_create(&pid,NULL,thr_fn,NULL);
       printf("main thread\n");
       exit(0);
}

The output can be any of these:

    1.main thread 
      New thread
    2.main thread
    3.main thread
      New thread
      New thread

First and second are convincing . But can anybody explain the reason behind the third optional output.

Answer 1

I’m quite sure, that your program does not create two threads 😉

Most likely you see the effects of a race-condition on stdout between your new thread and the main thread. exit flushes and closes all streams. This might happen non-atomically and in parallel to the other thread writing into the same stream buffer and flushing that also to the file descriptor.