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From: discolo@ucsbcsl.UUCP (Anthony V. Discolo)
Newsgroups: net.unix-wizards
Subject: 4.2BSD signal question.
Message-ID: <158@ucsbcsl.UUCP>
Date: Thu, 30-Aug-84 14:10:36 EDT
Article-I.D.: ucsbcsl.158
Posted: Thu Aug 30 14:10:36 1984
Date-Received: Mon, 3-Sep-84 08:44:25 EDT
Organization: U.C. Santa Barbara
Lines: 64

A friend of mine had an interesting problem with signals.  He has a
program that catches SIGHUP and SIGQUIT.  When the process is stopped,
sending it a SIGHUP will restart it, but sending it a SIGQUIT will not
restart it.  The SIGQUIT signal is received when the process is 
restarted, either by a SIGQUIT, or by a SIGCONT.

For example, a.out continuously prints periods, it will print an H
when it receives a SIGHUP, and it will print a Q when it receives
a SIGQUIT.  The following is a script that should explain the situation.
My comments are within {}.

			% a.out > OUT
			^Z
			Stopped
			% cat OUT
			......................
			% cat OUT
			......................
			{ a.out is stopped and is not printing
			periods at this time }
			% jobs
			[1] + Stopped		a.out
			% kill -HUP %1
			% cat OUT
			......................H.........
			% cat OUT
			......................H......................
			{ a.out has received the SIGHUP, and has
			been restarted }
			% jobs
			[1] + Stopped		a.out
			{ csh doesn't know that the process has been 
			restarted }
			% fg
			^Z
			Stopped
			% kill -QUIT %1
			% cat OUT
			......................H..........................
			% cat OUT
			......................H..........................
			{ a.out has not received the SIGQUIT yet, and has
			not been restarted }
			% fg
			^Z
			% cat OUT
			......................H..........................Q...
			% cat OUT
			......................H..........................Q..........
			{ now a.out has received the SIGQUIT and is running }

Can someone please explain to me in detail why this is so?  I've briefly
searched the source code, but haven't found an explanation.

Please reply by mail, and I'll post satisfactory explanations.
-- 

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