On Sat, Nov 30, 2019 at 01:16:30PM -0800, Junio C Hamano wrote:
> SZEDER Gábor <szeder.dev@xxxxxxxxx> writes:
>
> > + (
> > + git fast-import $options <&8 >&9 &
> > + echo $! >V.fi.pid
> > + wait $!
> > + echo >&2 "background fast-import terminated too early with exit code $?"
> > + # Un-block the read loop in the main shell process.
> > + echo >&9 UNEXPECTED
> > + ) &
> > + echo $! >V.sh.pid
> > # We don't mind if fast-import has already died by the time the test
> > # ends.
> > - test_when_finished "
> > + test_when_finished '
> > exec 8>&-; exec 9>&-;
> > - kill $(cat V.pid) && wait $(cat V.pid)
> > - true"
> > + kill $(cat V.sh.pid) && wait $(cat V.sh.pid)
> > + kill $(cat V.fi.pid) && wait $(cat V.sh.pid)
> > + true'
>
> The original interpolates the PID of the fast-import when
> "when-finished" program is registered, so it is OK if somebody else
> removed V.pid file; the new one interpolates when "when-finished"
> program is run, reading from V.??.pid, so somebody needs to make
> sure these pid files will stay around. I do not think it is an
> issue as I suspect we've left it to the global clean-up procedure
> that removes the trash directory to remove the pid file.
In the original the same shell process starts 'git fast-import',
writes its pidfile, and registers the test_when_finished commands, so
we can be sure that the pid file is already present when the shell
runs the $(cat V.pid) command substitutions.
With this patch that's not the case anymore, because the background
subshell starts 'git fast-import' and writes the pidfile, but the main
shell process registers the test_when_finished commands. IOW these
two shell processes are racing, and it's possible that the
test_when_finished command is executed before the background subshell
can write the pidfile. So double quotes around the block of
test_when_finished commands are not good.
> By the way, does the second "kill && wait" wait for the right
> process?
Ouch, it clearly doesn't. Copy-paste error I suppose.
Thanks for spotting it.
>
> > background_import_still_running () {
> > - if ! kill -0 "$(cat V.pid)"
> > + if ! kill -0 "$(cat V.fi.pid)"
> > then
> > echo >&2 "background fast-import terminated too early"
> > false
> > fi
> > }
