On Wed, Jan 25, 2023 at 12:06:25PM +0600, NRK wrote:
> On Tue, Jan 24, 2023 at 09:01:08PM +0100, Hiltjo Posthuma wrote:
> > Although of course checking errno on a success condition is a bit wonky in
> > this test case.
>
> It was just an illustration that the malloc succeeded :)
> A more real-world check would be something like this (in fact, I'm quite
> sure this is precisely the cause of the xlib XIO error):
>
> if (poll(...) < 0) {
> if (errno == EINTR)
> continue;
> else
> error(...);
> }
>
> > What about a simplified version of a patch below, it should do a similar
> > thing:
> >
> > /* clean up any zombies immediately */
> > - sigchld(0);
> > + if (signal(SIGCHLD, SIG_IGN) == SIG_ERR)
> > + die("can't ignore SIGCHLD:");
>
> One issue here is that this will not clean up any existing zombies
> (inherited from .xinitrc etc).
>
> That's what that "clean up any zombies immediately" comment is referring
> to. I think that comment ought to be a bit more descriptive and mention
> where these zombies are coming from since it's not immediately obvious.
>
> One other thing worth mentioning is that this behavior wasn't well
> defined on earlier POSIX versions so some historical BSDs may have
> different behavior. From
> (https://man7.org/linux/man-pages/man2/sigaction.2.html#NOTES):
>
> | POSIX.1-1990 disallowed setting the action for SIGCHLD to
> | SIG_IGN. POSIX.1-2001 and later allow this possibility, so that
> | ignoring SIGCHLD can be used to prevent the creation of zombies.
> | Nevertheless, the historical BSD and System V behaviors for ignoring
> | SIGCHLD differ
>
> The POSIX manpage for signal(3p) also says that "new applications should
> use sigaction() rather than signal()" - probably due to these
> incompatibility reasons.
>
> But in any case, if you don't want to use `sigaction`, I think reaping
> the existing zombies after the `signal` call _should_ work:
>
> - /* clean up any zombies immediately */
> - sigchld(0);
> + if (signal(SIGCHLD, SIG_IGN) == SIG_ERR)
> + die("can't ignore SIGCHLD:");
> + /* clean up any zombies (inherited from .xinitrc etc)
> immediately */
> + while (waitpid(-1, NULL, WNOHANG) > 0);
>
> I haven't tested (or even compiled) the above patch. And it seems that
> signals (much like threads) are really easy to mess up, so feel free to
> correct if anything is wrong.
>
> - NRK
>
I don't think there can be any zombies since it is run in setup() before any
processes can spawn (via keybindings etc) or am I overlooking something
obvious?
--
Kind regards,
Hiltjo
