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Re: [PATCH] t6500: don't run detached auto gc at the end of the test script

On Mon, Apr 10, 2017 at 02:59:11PM +0200, SZEDER Gábor wrote:

> While this change doesn't completely eliminate the possibility of
> this race, it significantly and seemingly sufficiently reduces its
> probability.  Running t6500 in a loop while my box was under heavy CPU
> and I/O load usually triggered the error under 15 seconds, but with
> this patch it run overnight without incident.
> (Alternatively, we could check the presence of the gc.pid file after
> starting the detached auto gc, and wait while it's there.  However,
> this would create a different race: the auto gc process creates the
> pid file after it goes to the background, so our check in the
> foreground might racily look for the pid file before it's even
> created, and thus would not wait for the background gc to finish.
> Furthermore, this would open up the possibility of the test hanging if
> something were to go wrong with the gc process and the pid file were
> not removed.)

Could we just leave open a pipe descriptor that the child inherits, and
wait for it to close?

Something like:

  git gc --auto 9>&1 | read

should wait until the background gc process finishes. It depends on our
daemonize() not closing descriptors beyond 0/1/2, but that is certainly
the case now.

It also loses the exit status of the main "git gc", but that can be
fixed with shell hackery:

  code=$(sh -c 'git gc --auto; echo $?' 9>&1)
  test "$code" = 0