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

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

On Mon, Apr 1, 2013 at 11:14 PM, Jeff King [off-list ref] wrote:

quoted

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

quoted

quoted

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