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From: simon@its63b.ed.ac.uk (Simon Brown)
Newsgroups: comp.unix.wizards
Subject: Re: No more signals
Message-ID: <492@its63b.ed.ac.uk>
Date: Sun, 21-Jun-87 18:07:03 EDT
Article-I.D.: its63b.492
Posted: Sun Jun 21 18:07:03 1987
Date-Received: Fri, 26-Jun-87 03:46:39 EDT
References: <48300005@hcx1> <1714@munnari.oz>
Reply-To: simon@its63b.ed.ac.uk (Simon Brown)
Organization: Computer Science Department, Edinburgh University
Lines: 45

In article <1714@munnari.oz> kre@munnari.oz (Robert Elz) writes:
>In article <48300005@hcx1>, tomp@hcx1.SSD.HARRIS.COM writes:
>> a mask of the signals and checks it in such places as system call entry/exit.
>> ... the signal mask is checked in critical places.
>
>I think you'll find that the vast majority of the checks (executed)
>are actually "is there a signal", the code doesn't care which signal
>is pending, only whether one is.
>
>You could implement the signal pending and mask stuff anyway that
>you like from this point of view, only the signal sending, and delivery
>code care about this part of things, and they're not time critical,
>so indexing into an array of bits would be reasonable.

One really nasty bug that really needs fixing fast is that the so-called
"safe signal" mechanism is anything but! If I send 5 SIGINT signals to a
process, there is no guarentee that that process will receive them all - ok,
it will certainly receive at least one, but whether it receives 2,3,4 or 5
is pretty much left to chance!

>
>However, there's a problem with any change here .. he user interface
>assumes that the signal bits can be implemented by a bit mask of 32
>bits (actually an "int" which we hope like hell has NSIG (32) bits
>in it).
>
Yes, but you can always build a little backward-compatibility library to
allow people to still use bitmasks if they want to.

Also, if your "int" doesn't have 32 bits, then you should be using a "long"
instead, for this - like 2.9BSD does.


	%{
	    Simon!
	%}


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| Department of Computer Science | JANET: simon@uk.ac.ed.its63b
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