Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!van-bc!sl
From: sl@van-bc.UUCP (pri=-10 Stuart Lynne)
Newsgroups: comp.unix.wizards
Subject: signal(SIGCLD,SIG_IGN)
Keywords: race condition
Message-ID: <2371@van-bc.UUCP>
Date: 15 Apr 89 07:40:15 GMT
Organization: Public Access Network, Vancouver, BC.
Lines: 39

Under SYS V SIGCLD has special behaviour depending on what you pass to the
signal system call.

Specifically if SIG_IGN is used a parent process calling wait() will block
until all child processes die, and child processes will not become zombies
when the exit.

If SIG_DFL is used the parent process will proceed from a wait() after any
child process terminates and child processes will become zombies until the
parent process excutes a wait.

The question is:

	If there are child processes in the zombie state when signal(SIGCLD,
	SIG_IGN) is executed will they be terminated?


For example in the following code fragment is there a race condition between
the wait() call and the following signal(SIGCLD,SIG_IGN) call?

	while (1) {
		while(findajob()) {
			if (cantfindslot()) {
				signal(SIGCLD,SIG_DFL);
				wait(&rc);		/* race here */
				signal(SIGCLD,SIG_IGN);	/* race here */
			}	
			startthejob();
		}
		sleep(30);
	}
  
It seems to be ok. Can anyone who has seen the inner workings of signal()
comment?

--
Stuart.Lynne@wimsey.bc.ca uunet!van-bc!sl 604-937-7532(voice) 604-939-4768(fax)
-- 
Stuart.Lynne@wimsey.bc.ca uunet!van-bc!sl 604-937-7532(voice) 604-939-4768(fax)