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From: jsq@ut-sally.UUCP (John Quarterman)
Newsgroups: net.unix-wizards
Subject: Re: New? idea
Message-ID: <783@ut-sally.UUCP>
Date: Mon, 16-Jan-84 13:43:35 EST
Article-I.D.: ut-sally.783
Posted: Mon Jan 16 13:43:35 1984
Date-Received: Tue, 17-Jan-84 02:38:49 EST
References: <4771@umcp-cs.UUCP>
Organization: U. Texas CS Dept., Austin, Texas
Lines: 52

x
	From: chris@umcp-cs.UUCP
	Subject: New? idea
	Message-ID: <4771@umcp-cs.UUCP>
	Date: Sun, 15-Jan-84 17:43:17 CST
	
	Something that network servers often do is

		while ((netfd = netopen ()) >= 0) {
			if ((pid = fork ()) == 0) {
				if (fork ())
					exit (0);
				workhorse ();
				exit (0);
			}
			close (netfd);
		}

	The purpose of the double-fork is to "disown" the actual worker and
	let the server continue to accept network connections.  Without the
	"disownment", when the "workhorse" finishes and exit()s, it hangs around
	forever taking up a process slot, just so that it can return its status
	to its parent.  But the server doesn't care, ergo the double-fork-be-
	inherited-by-init trick.

	So, my suggestion is a "disown" system call, to allow parents to give
	up their children so that on exit they will vanish without a trace.
	Does anyone know why this should not be implemented (other than because
	you can do it without this)?  Alternatively, does anyone have better
	ideas?
	
That's called a spawn.  For it to work correctly, you need to have a wait:

	while ((netfd = netopen ()) >= 0) {
		if ((pid = fork ()) == 0) {
			if (fork ())
				exit (0);
			workhorse ();
			exit (0);
		}
		wait (0);	/* clean up child, leave granchild */
		close (netfd);
	}

and some error checking and fork retrying is quite useful in practice.

I prefer SIGCHLD, myself.  It's too bad select wasn't made general enough
to allow selecting on dead or stopped processes as well as file and socket
conditions.
-- 
John Quarterman, CS Dept., University of Texas, Austin, Texas
{ihnp4,seismo,ctvax}!ut-sally!jsq, jsq@ut-sally.{ARPA,UUCP}