On Thu, Sep 30, 2010 at 4:15 PM, Junio C Hamano <gitster@xxxxxxxxx> wrote:
> Ævar Arnfjörð Bjarmason <avarab@xxxxxxxxx> writes:
> > FWIW I think this is more readable, but maybe we want to retry on all
> > platforms:
> >
> > my $fh;
> > if ($^O eq 'MSWin32' or $^O eq 'cygwin') {
> > # Try 10 times to open our lock file, in case Windows is lagging
> > for my $try (1..10) {
> > sysopen($fh, $db_lock, O_RDWR | O_CREAT);
> > last if $fh;
> > }
> > } else {
> > sysopen($fh, $db_lock, O_RDWR | O_CREAT);
> > }
> >
> > warn "Couldnt open $db_lock: $!\n" unless $fh;'
I agree that this is more readable, although I don't think there needs
to be separate code sections for each OS. If it's a good OS, it will
only loop once. You would want to die or croak instead of warn,
though. It needs the lock to continue, right?
> What exactly does "Windows is lagging" mean in the above?
>
> Why does sysopen() randomly fail and why does it succeed (sometimes) when
> it immediately gets retried with the same argument? Is this a shared lock
> and is used by some other processes that drive git? Why does the issue
> manifest only on Windows? If there are competing processes, wouldn't it
> exacerbate the situation to run a tight loop to try grabbing the lock
> without waiting, like the above patch does?
All very good questions, and I don't know most of the answers. I know
that sysopen() is just a thin wrapper around the 'open' system call,
so the problem has to be with Windows somehow. It probably doesn't
happen with other OSes because they're better at files :P
I have verified (to the best of my ability) that this problem happens
even when TortoiseGit is not running, and I don't have cheetah
installed, and there are no other 'git.exe's running. I considered
putting some sort of sleep() in there, but since it worked so well
without the sleep (it only retried once at most). Fetching multiple
revisions is slow anyways, so I don't think a 2-second wait would
hurt, though.
-Nate
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html