Re: Darcs-git: a few notes for Git hackers

["H. Peter Anvin" <hpa@zytor.com>]

Juliusz Chroboczek wrote:
>>>I see.  Let me know if you decide to use a different name for the
>>>lock file so I can switch to using the same one as yours.
> 
> 
>>Are you using flock(), or some other contraption that breaks if a
>>process dies unexpectedly?
> 
> No, I'm using a file that is created by the NFS-safe equivalent of
> open(O_CREAT | O_EXCL).  This is what Darcs has been doing basically
> forever.
> 
> Darcs usually doesn't die unexpectedly -- it's a Haskell program, so
> bugs usually manifest themselves with an exception being thrown
> allowing Darcs to clean-up after itself.
> 
> The one exception is when Darcs gets killed by the OOM killer (which,
> as you doubtless know, doesn't give any advance warning to a process,
> thus making it impossible for a process to deal with it gracefully).
> In such cases, manual intervention is necessary anyway -- a file could
> have been written half-way.
> 

In the case of git, it should not be necessary even then; there might be 
a broken file in the repository but nothing would reference it so it 
shouldn't have any effect.  Functionally speaking, operations on the git 
repository are in themselves atomic.

	-hpa