Re: 1.3.20 : getpgid returns pid != -1 when specified pid no longer exists

[gavin bowlby <gavin_bowlby@yahoo.com>]

>Ok.  In that event, please provide a simple test
case.

Christopher, Corinna:

Thanks for you help on this!

Here's a short program to recreate this problem:

("main.c")
=====================================================
int main(int argc, char *argv[]) {

   int pid, sid, rc;

   if ((pid = fork()) == 0) {
      // child thread
      pid = getppid();
      while(1) {
         rc = sleep(10);
         printf("child is alive...\n");
         if ((sid = getpgid(pid)) == -1) {
            printf("exiting child process...rc=2\n");
            exit(2);
         }
      }
   }
   else {
      // parent thread
      while(1) {
         rc = sleep(10);
         printf("parent is alive...\n");
         // check if our child process has been killed
         if ((sid = getpgid(pid)) == -1)
            exit(3);

         printf("getpgid of child pid:%d returned
pid:%d\n", pid, sid);
      }
   }
}
==========================================
and here are the steps I used to find the problem:

1) bring up Cygwin shell 1
2) gcc main.c <create executable>
3) a.exe <run executable>
4) let program run 10-15 seconds to see output from
    parent and child
5) bring up Cygwin shell 2
6) ps <to see PIDs of parent and child>
7) kill -9 <child PID>
8) observe that parent continues to run, and sees
   the parent's PID reported as the result of the
   getpgid

BTW, the same problem occurs if the parent PID is
killed - the child continues to see that the parent
PID is alive.

The general problem I'm trying to solve here is:

Given a long-lived parent process and a long-lived
child process, I want the parent and child to be able
to detect if the child or parent has died, and if so,
exit.

Thanks again for your kind assistance.

Gavin Bowlby
<gavin_bowlby@yahoo.com>


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