From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <junkio@cox.net>
Subject: Re: Question about possible git races
Date: Wed, 22 Mar 2006 16:24:58 -0800
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To: Radoslaw Szkodzinski <astralstorm@o2.pl>
In-Reply-To: <200603201724.12442.astralstorm@o2.pl> (Radoslaw Szkodzinski's
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Radoslaw Szkodzinski <astralstorm@o2.pl> writes:

> - push vs pull
>
> - push vs push
>
> - fetch vs fetch

About push vs push, with "really bare git", I take it that you
mean two send-pack from remote sites running two receive-pack
simultaneously.

There is an explicit race avoidance between the receive-pack
processes.  When a ref (either branch head or a tag) is updated,
it does:

 - read the current value from the ref.
 - do its work.
 - lock to prevent others to create the temporary file for
   updating the ref.
 - create the temporary file for the ref and write the new value.
 - check if the ref's value has not changed from what it
   initially read;
 - rename the temporary file to the ref to unlock.

Read receive-pack.c::update() for exact details if you are
interested.

> I'm meaning really bare git there, w/o bash+perl scripts.

The question does not make any sense for other cases, because
branch update by fetch and pull are all scripts based.