From: SZEDER Gábor <szeder@ira.uka.de>
Date: Thu, 05 May 2016 15:14:30 GMT
Subject: Re: [PATCH] t5510: run auto-gc in the foreground
Message-ID: <20160505171430.Horde.-GuvDpZBfS8VI1Zcfn4bJQI@webmail.informatik.kit.edu>
In-Reply-To: <alpine.DEB.2.20.1605040741500.9313@virtualbox>


Quoting Johannes Schindelin <Johannes.Schindelin@gmx.de>:

> Hi Gábor,
>
> On Tue, 3 May 2016, SZEDER Gábor wrote:
>
>> 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()?
>
> 			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"));

It is only correct as far as the value of the 'gc.autoDetach' config
variable is concerned, which is enabled by default, even on Windows, where
it can't go to the background.

> (should it really know that we cannot daemonize()?
> What about other code paths using that function?):

daemonize() is currently only used in the 'git gc --auto' code path and in
'git daemon', which doesn't announce that it is about to go in the
background.  Then there is the WIP index-helper, which will use daemonize()
as well, but it won't announce that either.

Being the sole callsite that makes such an announcement, I think it should
know or at least should check whether "daemonizing" is possible. (as
opposed to e.g. teaching daemonize() to print such messages)


Gábor