Date: Fri, 11 Dec 1998 11:40:58 -0800 (PST) From: Archie Cobbs <archie@whistle.com> To: peter.edwards@isocor.ie (Peter Edwards) Cc: dillon@apollo.backplane.com, jwd@unx.sas.com, freebsd-current@FreeBSD.ORG Subject: Re: inetd: realloc/free bug Message-ID: <199812111940.LAA27652@bubba.whistle.com> In-Reply-To: <3670EC02.D35D99CC@isocor.ie> from Peter Edwards at "Dec 11, 98 01:55:14 am"
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Peter Edwards writes:
> > It's not trivial if you want to guarantee that no signals are missed.
> > There's no way atomically to: unblock signals and call select().
>
> Hmm. I must be twisted.
> What horror results from doing this in a signal handler? On e-paper, it
> seems to give the desired effect, but does a return from a signal
> handler implicitly call sigreturn(2) when it returns? And if so, is
> there anything that requires this to happen?
I guess I was thinking in terms of the event library model; that is,
you don't handle the signal event in the signal handler (because in
general the event handler could call malloc(), etc), but rather you
simply set a flag (call it "signalFlag").
The race condition is getting a signal between the first and second
lines below:
sigprocmask(SIG_UNBLOCK ..) /* unblock signals */
r = select(...) /* wait for event */
sigprocmask(SIG_BLOCK ..) /* block signals */
if (signalFlag || r > 0) {
... /* handle event(s) */
}
But there are probably smarter ways to do it than this.
-Archie
___________________________________________________________________________
Archie Cobbs * Whistle Communications, Inc. * http://www.whistle.com
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