Date: Sat, 29 Sep 2001 21:43:38 +0100 From: David Taylor <davidt@yadt.co.uk> To: freebsd-hackers@FreeBSD.org Subject: Re: Doubt of system(3) Message-ID: <20010929214338.A57903@gattaca.yadt.co.uk> In-Reply-To: <20010929153433.U59854@elvis.mu.org>; from bright@mu.org on Sat, Sep 29, 2001 at 15:34:33 -0500 References: <200109291527.f8TFRrU76727.toshi@jp.FreeBSD.org> <20010929153433.U59854@elvis.mu.org>
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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.
> >=20
> > default: /* parent */
> > do {
> > pid =3D _wait4(pid, &pstat, 0, (struct rusage *=
)0);
> > } while (pid =3D=3D -1 && errno =3D=3D EINTR);
> > break;
> >=20
> > Please review and commit this patch.
>=20
> 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'.
>=20
> What's a, b and c?
>=20
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 [=3D11], ...);
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 =3D=3D -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...)
--=20
David Taylor
davidt@yadt.co.uk
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