Thomas Munro <thomas.munro@gmail.com> writes:
> Did I understand correctly that the places that do kill(-pid) followed
> by kill(pid) really only need the kill(-pid)?
Uh ... did you read the comment right above signal_child?
* There is a race condition for recently-forked children: they might not
* have executed setsid() yet. So we signal the child directly as well as
* the group. We assume such a child will handle the signal before trying
* to spawn any grandchild processes. We also assume that signaling the
* child twice will not cause any problems.
It might be that this is wrong and signaling -pid will work even if
the child hasn't yet done setsid(), but I doubt it: the kill(2) man
page is pretty clear that it'll fail if "the process group doesn't
exist".
Perhaps we could finesse that by signaling -pid first, and then
signaling pid if that fails, but offhand it seems like that has
the described race condition w.r.t. grandchild processes.
regards, tom lane
