"Zombies are created when a child has exited, but the parent has not wait()ed for it yet."

We have a little bit misunderstanding of "zombie" here ;-) Zombie is actually a process still running, but we lost track of it. In other words, in the fork case, if the parent created a child that cannot exit on its own, say it has some sort of dead loop, whatever the dead loop is created by mistake or purposely, as a good practice, the parent process should kill the child process. Otherwise, the child becomes a zombie, as it will run forever, and it will have that seat in the process table forever.

If a process exited, it will be removed from the process table, doesn't matter whether it is created by a parent process, or it runs on its own, as it is a process any way.

Other than the zombie situation, there are also other cases you may want to waitpid on your child process. For example, a parent process keeps creating child processes, and delegating tasks to them at a high speed. If you don't waitpid() to control the number of child processes you created and still alive, you would soon see an error message saying that, you cannot create child process, as resource used up.

In this case, you would keep a counter of running child processes, and when it reaches a predefined max, stop creating child process, and start waitpid(), until the number of running child processes drop below a safe line.

Also a little comment about SIGCHLD. You cannot capture SIGCHLD on win32, so the approach is not fully portable.

In reply to Re: Re: open(KID, "-|") and wait()? by pg
in thread open(KID, "-|") and wait()? by edan

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