parent process and child processes, if one exits, how to inform the other exits?

Question

If I spawn a process in my linux C program and there are 2 processes in total, a parent process and a child process. I want: if one of these 2 processes exits, the other process also exits.

How to achieve this? are there any similar source codes?

Note: I don't want to block both processes, e.g, I don't want the parent process to be blocked by wait()

thanks!

Check http://stackoverflow.com/questions/2377811/tracking-the-death-of-a-child-process — VoidPointer, Jul 01 '13 at 16:31
Read http://advancedlinuxprogramming.com/ which has a full chapter to answer that. — Basile Starynkevitch, Jul 01 '13 at 16:35

hek2mgl · Accepted Answer · 2013-07-01T17:04:02.163

In father process you can use the waitpid system call. It will block until the child exits.

In the child process you cannot use waitpid. One option would be that the father will inform the child by sending it a SIGTERM on exit. But this will only work if the father won't get killed using SIGKILL. I would suggest to periodically send a signal using kill with param 0 to the father process. If this fails, the process has terminated.

From the kill(2) man page:

if sig is 0, then no signal is sent, but error checking is still performed; this can be used to check for the existence of a process ID or process group ID.

score 1 · Answer 2 · answered Jul 01 '13 at 16:29

1

If the child exits, the parent will be sent a SIGCHLD. If the parent is going to die, it should notify the child somehow, or at least send it a SIGTERM.

answered Jul 01 '13 at 16:29

Ignacio Vazquez-Abrams

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What if the father will be terminated using `SIGKILL`. Then the child won't recieve SIGTERM – hek2mgl Jul 01 '13 at 16:32
Then you can use a signalhandler function to do the cleanup. – Varvarigos Emmanouil Jul 01 '13 at 16:33
@V_Maenolis you cannot handle `SIGKILL` – hek2mgl Jul 01 '13 at 16:34
@hek2mgl That was my bad. I had forgotten. I just did a quick research. – Varvarigos Emmanouil Jul 01 '13 at 16:36
@V_Maenolis I would use `kill(pid, 0);` in the child process to check actively if the father is still alive. This can run in a separate thread if necessary. – hek2mgl Jul 01 '13 at 16:41

score 0 · Answer 3 · answered Jul 01 '13 at 16:28

0

http://linux.die.net/man/2/waitpid

Wait for any child process, then exit when you return from waitpid.

answered Jul 01 '13 at 16:28

KrisSodroski

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it is also possible that the parent process exits first – user1944267 Jul 01 '13 at 16:30
No, you just kill your child group when you exit out of the waitpid. Duh. Does every little thing have to be explicit? Its common sense, just like this question. – KrisSodroski Jul 01 '13 at 16:32

score -1 · Answer 4 · answered Jul 01 '13 at 16:29

-1

If the parent process exits, then the child process becomes a zombie process.

If the child exits, the parent can be notified by the wait system call. You can exit the parent by reading the status of it.

answered Jul 01 '13 at 16:29

bazzinga

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If the parent exits, the child is inherited by `init` that is pid 1 by defintion. A child becomes a zombie if its own dead is not handled by (current) the parent. – alk Sep 07 '13 at 17:14

parent process and child processes, if one exits, how to inform the other exits?

4 Answers4