Re: [PATCH] t5510: run auto-gc in the foreground

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: May 4, 2016, 05:48 UTC
Message-ID: <alpine.DEB.2.20.1605040741500.9313@virtualbox>
In-Reply-To: <20160503135028.Horde.jeJdKT1kb2NTVAS1HpcsQh2@webmail.informatik.kit.edu>

Hi Gábor,

On Tue, 3 May 2016, SZEDER Gábor wrote:

Show 34 quoted lines

> Quoting SZEDER Gábor <szeder@ira.uka.de>:
> 
> >Quoting Johannes Schindelin <Johannes.Schindelin@gmx.de>:
> >
> > >Hi Gábor,
> > >
> > >On Sun, 1 May 2016, SZEDER Gábor wrote:
> > >
> > > >diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
> > > >index 38321d19efbe..454d896390c0 100755
> > > >--- a/t/t5510-fetch.sh
> > > >+++ b/t/t5510-fetch.sh
> > > >@@ -682,6 +682,7 @@ test_expect_success 'fetching with auto-gc does
> > > >not lock up' '
> > > > (
> > > >  cd auto-gc &&
> > > >  git config gc.autoPackLimit 1 &&
> > > >+		git config gc.autoDetach false &&
> > > >  GIT_ASK_YESNO="$D/askyesno" git fetch >fetch.out 2>&1 &&
> > > >  ! grep "Should I try again" fetch.out
> > > > )
> > >
> > >Sounds good to me.
> >
> >There is something still bothering me, though.
> >
> >I take this was a Windows-specific issue; deleting open files on Linux is
> >no brainer.  According to a comment on the original Git for Windows issue
> >at github[1], 'git gc' runs in the background by default on Windows as well.
> 
> Ok, having slept on it, it was a false alarm.
> 
> Though 'git gc --auto' claims "Auto packing the repository in background for
> optimum performance." on Windows, it does in fact runs in the foreground.

Thanks for checking. I ran out of time yesterday.

> 'git gc --auto' first prints that message, unless gc.autoDetach is disabled,
> and then calls daemonize() to go to the background.  However, daemonize() is
> basically a no-op on Windows, thus 'git gc' will remain in the foreground and
> the sequence I described below is impossible.  Good.

Oh, right. I think this will take a lot of energy to fix: daemonize()'s functionality is not really available, indeed. What *is* available is a spawn() that detaches the new process.

> Perhaps it would be worth updating 'git gc' to not lie about going to the
> background when we can already know in advance that it won't.

Hmm. https://github.com/git/git/blob/master/builtin/gc.c#L372-L373 already looks correct (should it really know that we cannot daemonize()? What about other code paths using that function?):

			if (detach_auto)
				fprintf(stderr, _("Auto packing the repository in background for optimum performance.\n"));
			else
				fprintf(stderr, _("Auto packing the repository for optimum performance.\n"));

Ciao, Dscho