bzr, rsync, and atomic operations

[John Arbash Meinel]

Jan Hudec wrote:
> On Thu, Oct 13, 2005 at 13:41:42 -0500, John Arbash Meinel wrote:
> 
>>Well, for bzr, almost all writes to a file are done through "AtomicFile"
>>which means it writes to a temporary and copies it across.
> 
> 
> Does it work on Windows too? I know how atomic writes are done on POSIX
> using rename, but I am not sure Windows have the same semantics.

Well, we don't have truly atomic writes on windows. We still write to a
temporary, but instead of renaming over the existing file, we have to
delete it, and then rename into its place.
So it is "almost-atomic". It still is consistent, you just might end up
with nothing if something is interrupted at exactly the right time.

(Speaking of which, we probably should put in a couple of catches for
common exceptions like KeyboardInterrupt, to keep things working even then.)

> 
> Also where does the module come from? I can't seem to find it in python
> documentation nor in the cheese shop.

It is in the bzrlib source code. Not a separate module.
(bzrlib/atomicfile.py)

John
=:->

> 
> --
> 						 Jan 'Bulb' Hudec <bulb at ucw.cz>

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