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From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga
Subject: Re: Endless WaitIO() in VT100
Message-ID: <31537@sun.uucp>
Date: Wed, 21-Oct-87 14:07:59 EDT
Article-I.D.: sun.31537
Posted: Wed Oct 21 14:07:59 1987
Date-Received: Sat, 24-Oct-87 06:21:58 EDT
References: <16584@amdahl.amdahl.com>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 28

In article <16584@amdahl.amdahl.com> acs@amdahl.amdahl.com (Tony Sumrall) writes:
}
}Ed Puckett has zeroed in on an AbortIO()/WaitIO() bug that is present in
}VT100 R2.7 but was present back in R2.6 days.  The problem appears to be
}that sometimes, after an AbortIO(), the subsequent WaitIO() is never
}satisfied.  Way back when this problem was originally discussed, Neil
}Katin of Commodore said that the AbortIO() should be followed by a
}Wait()/GetMsg() pair or, alternatively, a WaitIO() since the abort doesn't
}remove the reply.  Ed changed the WaitIO() with a GetMsg() call with no
}intervening Wait() and, he reports, the problem disappears!
}
}Anyone got the straight scoop?  Doesn't seem that, in a message passing
}system, one should simply do a GetMsg() without a preceeding Wait().

Actually, there is a definite race condition when you use AbortIO to 
abort a request. Since the request may actually finish just before the
call to AbortIO, if you then do a WaitIO you will never return because
the there is no request there! So you probably want to add a call to 
CheckIO to make sure the request still exists before waiting on it, thus
the code would look something like ...

	AbortIO(request);
	if (CheckIO(...)) WaitIO(request);


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.