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From: lm@slovax.Eng.Sun.COM (Larry McVoy)
Newsgroups: comp.unix.wizards
Subject: Re: lost of SIGIO in SunOS4.1/4.0.3
Message-ID: <613@appserv.Eng.Sun.COM>
Date: 30 May 91 21:56:13 GMT
References: <27061@adm.brl.mil>
Sender: news@appserv.Eng.Sun.COM
Organization: Sun Microsystems, Mt. View, CA.
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TAYBENGH%NUSDISCS.BITNET@cunyvm.cuny.edu (THE AGEIS) writes:
> found out SOME (not ALL - the last few sent) SIGIO signals are lost.
> I thought SunOS4.1 provides reliable signal as described by Steven in his

It is the intent that SunOS provided "normal" unix signals.  To wire
your brain properly, think of Unix as a processor, system calls as
instructions, and signals as interrupts.  That said, you may remember
that multiple unhandled interrupts get coalesced into one, in other
words, when you handle the interrupt the handler can't tell if it has
received 1 or 20 since the last time it handled the interrupt.  An
interrupt (and a Unix signal) just sets a bit in a mask.  The bit is
just one bit, you can set it 20 times but it still "1".

The problem is that the sending app is counting on the receiving app to 
handle each signal one at a time.  The sender's and reciever's idea of
the number of signals sent will get out of wack when the system gets busy.
---
Larry McVoy, Sun Microsystems     (415) 336-7627       ...!sun!lm or lm@sun.com