lock free dirstate

[John Arbash Meinel]

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Robert Collins wrote:
> I plan to do an experiment this week on an OSLock free dirstate - this
> should work more robustly on NFS, AFP etc. I've tagged the bugs that
> stood out as being fixed by this as 'dirstate2' in launchpad.
> 
> The design I plan to use is the one that I've spoken about before:
>  - write a collection of dirstate files named by hash (like we do
> in .bzr/repository)
>  - have old dirstate files attempt to rm but handle them being open by
> other processes by leaving them behind
>  - have a near-atomic pointer file in the root that is updated by the
> standard foo.tmp, mv foo foo.old, mv foo.tmp foo, rm foo.old code

^- Presumably you don't need to 'mv foo foo.old' on POSIX platforms?

> 
> I figure this should be pretty straight forward to hook in. It will mean
> a new tree format, but if successful will allow 'bzr diff' from a commit
> editor to work and so forth.
> 
> If there are any objections to this design, please speak up now!
> 
> -Rob

It sounds reasonable to me.

John
=:->
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