Date: Sat, 29 Sep 2001 16:05:00 -0500 From: Alfred Perlstein <bright@mu.org> To: David Taylor <davidt@yadt.co.uk> Cc: freebsd-hackers@FreeBSD.org Subject: Re: Doubt of system(3) Message-ID: <20010929160500.X59854@elvis.mu.org> In-Reply-To: <20010929214338.A57903@gattaca.yadt.co.uk>; from davidt@yadt.co.uk on Sat, Sep 29, 2001 at 09:43:38PM %2B0100 References: <200109291527.f8TFRrU76727.toshi@jp.FreeBSD.org> <20010929153433.U59854@elvis.mu.org> <20010929214338.A57903@gattaca.yadt.co.uk>
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* David Taylor <davidt@yadt.co.uk> [010929 15:44] wrote:
> On Sat, 29 Sep 2001, Alfred Perlstein wrote:
> > * Toshihiko ARAI <toshi@jp.FreeBSD.org> [010929 11:10] wrote:
> > > I consider the following code of system(3). pid is changed by return
> > > value of _wait4(). I feel this need a correction.
> > >
> > > default: /* parent */
> > > do {
> > > pid = _wait4(pid, &pstat, 0, (struct rusage *)0);
> > > } while (pid == -1 && errno == EINTR);
> > > break;
> > >
> > > Please review and commit this patch.
> >
> > Why does it need to be corrected? What sort of bad behaviour
> > are you seeing? You do 'a' and you see 'b' when you should
> > see 'c'.
> >
> > What's a, b and c?
> >
>
> Well, hypothetically (I have no time to attempt to set something up to test
> this), it looks to me like:
>
> If you:
>
> 1. Fork, and create a child (say, pid 10)
> 2. Call system, which forks and creates a child (say, pid 11)
> 3. Make the child (pid 10) exit now.
> 3. Interrupt the call to _wait4(pid [=11], ...);
>
> You _should_ see nothing happen. i.e. system() would simply loop again
> until the other child exits.
>
> However, what I think you'd see is system() setting pid == -1, calling
> _wait4(-1, ...); and _wait4() returning 10, and system() returning whilst
> your child is still running happily away.
>
> If I run out of bugs to squash in ircd, I might try to produce this (I
> suppose reproduce is the wrong word, since no one has reported it in the
> first place...)
Yes, makes sense.
--
-Alfred Perlstein [alfred@freebsd.org]
'Instead of asking why a piece of software is using "1970s technology,"
start asking why software is ignoring 30 years of accumulated wisdom.'
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