Re: [PATCH 1/4] run-command: add new check_command helper

From: Jeff King <peff@peff.net>
Date: Apr 2, 2013, 05:26 UTC
Message-ID: <20130402052630.GB22089@sigill.intra.peff.net>
In-Reply-To: <CAMP44s3oVJs_sWpemFVGSkj-u_SrjsxE1mYja+Scx3PTBXC67Q@mail.gmail.com>

On Mon, Apr 01, 2013 at 11:22:36PM -0600, Felipe Contreras wrote:

Show 15 quoted lines

> On Mon, Apr 1, 2013 at 11:14 PM, Jeff King <peff@peff.net> wrote:
> > 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.
> 
> It still can potentially stay in a loop for some cycles.

That should be OK; it's the same loop we use in wait_or_whine (and that is in fact how I managed to get the WNOHANG wrong, as I copied the loop from there but forgot to update the flag variable). A few cycles is OK, as it is really about handling a simultaneous signal; it should be rare that we loop at all, and even rarer to loop more than a single time. On Linux, I don't think we will ever get EINTR at all, according to the manpage; however, POSIX seems to allow EINTR even with WNOHANG.

-Peff