From: Jeff King <peff@peff.net>
Date: Tue, 02 Apr 2013 05:14:07 GMT
Subject: Re: [PATCH 1/4] run-command: add new check_command helper
Message-ID: <20130402051407.GA21906@sigill.intra.peff.net>
In-Reply-To: <CAMP44s3-DnBM7Tm_+igLN+c5MGrbJNXUBwcj1HvGCPEJEwJSBQ@mail.gmail.com>

On Mon, Apr 01, 2013 at 11:11:20PM -0600, Felipe Contreras wrote:

> > But if we know from reading waitpid(3) that waitpid should only fail due
> > to EINTR, or due to bogus arguments (e.g., a pid that does not exist or
> > has already been reaped), then maybe something like this makes sense:
> >
> >   while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
> >           ; /* nothing */
> 
> But we don't want to wait synchronously here, we just want to ping.

Yeah, sorry, I forgot the WNOHANG there.

> > After the fix above, yes; in the original we would always have exited
> > already.
> 
> No:
> 
> +       if (waiting != cmd->pid)
> +               return 1;
> 
> If waiting < 0, waiting != cmd->pid, and therefore this return is not
> triggered, and there's only one more return at the end of the
> function.

Are my eyes not working? If waiting < 0, then waiting != cmd->pid, and
therefore this return _is_ triggered.

-Peff