[misterhouse-users] Re: Zombie Processes

[Harald K. <ch...@po...>]

> My mh produces about two zombie processes everytime i reload/refresh a mh
> produced web page.  This problem does not seem to happen with the photo
> frame code however.

Generally speaking, one of two things has to happen:

1) If $SIG{CHLD} = "IGNORE" will automatically reap all children.
2) MH must call wait() or waitpid() to reap each child process. This is
   usually handled by installing a signal handler.

It looks like, at startup, A signal handler is installed for CHLD, which
reaps the process (except on FreeBSD for some reason). However, the code
isn't quite right.

UNIX does not signal once for each event; multiple signals are collapsed
into a single signal handler call. The current signal handler reaps one
child then returns; if multiple children exited before the signal
handler triggered, the rest will be left behind.

The perlfunc man page documents this 'standard' loop:

	use POSIX ":sys_wait_h";
	#...
	do {
		$kid = waitpid(-1,&WNOHANG);
	} until $kid == -1;

(The WNOHANG is necessary to prevent a blocking wait :-)

I also found at least one place in the code where SIGCHLD is reset to
IGNORE (in Voice_Text.pm), which would make the problem completely
disappear and may be why most of us don't see it.


As always, Bruce is the expert :-)

-- 
Harald Koch     <ch...@po...>