wait() and strace -f

Kurt Roeckx (Q@ping.be)
Tue, 18 Dec 2001 02:14:07 +0100


I got a weird problem here. I have a process that creates 2
childs, the first one dies very fast before the parent can call
wait(). When I strace -f this wait() doesn't clean up the zombie
as it should.

Note that this problem only happens when I have 2 childeren, use
strace -f, and call wait after the first child died. Just
strace, without strace, only 1 child, or call wait() after the
child died doesn't seem to cause the problem.

Btw, this is with 2.4.16.

Simple program to demostrate it:

int main()
{
int i;

if (!fork())
{
/* Child 1. */
return 0;
}

if (!fork())
{
/* Child 2. */
sleep(10);
return 0;
}

/* Parent. */
sleep(1);
wait(&i);
return 0;
}

Without strace -f, this program stops after 1 second and the
second child still lives for 9 seconds. With strace -f this
program stops after 10 second after the second child died.

I think it's related to strace being the "real" parent of the
child. But that doesn't really explain why I need 2 childs.

Kurt

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