title: thread termination issue (c programming)
body: <p>I'm working on an application for Linux in C which uses multiple threads. The threads which are spawned by the main function do most of the work, and therefore usually finish last. I'm seeing some strange behavior, and I believe it's due to the main thread terminating before the spawned threads have a chance to finish their jobs. Here's some sample code to illustrate what I'm talking about:</p>
  
  <pre><code>#define _POSIX_C_SOURCE 200112L
  #define _ISOC99_SOURCE
  #define __EXTENSIONS__
  #define _GNU_SOURCE
  
  #include &lt;pthread.h&gt;
  #include &lt;stdio.h&gt;
  
  void
  my_cleanup(void *arg)
  {
       printf("cleanup: %s\n", (char *)arg);
  }
  
  
  void *
  thread_stuff(void *arg)
  {
       printf("thread started\n");
       pthread_cleanup_push(cleanup, "running");
       if (arg)
            pthread_exit((void *)2);
       pthread_cleanup_pop(0);
       pthread_exit((void *)2);
  }
  
  
  int
  main()
  {
       int err;
       pthread_t tid1, tid2;
  
       err = pthread_create(&amp;tid1, NULL, thread_stuff, (void *)1);
       err = pthread_create(&amp;tid2, NULL, thread_stuff, (void *)1);
  
       sleep(10);                 /* change the value here if you want */
  
       return SUCCESS;
  }
  </code></pre>
  
  <p>When this code is run, the message from the cleanup function is printed twice, as it should be, but other times when it is run, I see the message printed only once sometimes, and other times I see it printed three times or not at all. You add in the sleep function in the main function to play with how long it takes the main function to terminate.</p>
  
  <p>What can I do to make the program run as it should? I suspect it has something to do with joining to the children, but I don't entirely understand the concept of a join or how to apply it to this situation.</p>
  
  <p>Thanks in advance!</p>