[MERGE] Faster LocalTransport.put() and append() methods.

[Robert Collins]

On Thu, 2006-06-15 at 05:23 +1000, Martin Pool wrote:
> On 14/06/2006, at 7:16 PM, Robert Collins wrote:
> 
> > On Wed, 2006-06-14 at 13:36 +1000, Martin Pool wrote:
> >
> >> Since you're creating the file with O_EXCL I don't see any need to
> >> include the PID.  Instead, if that fails with EEXIST then just e.g.
> >> add a sequence number and try again.
> >
> > O_EXCL is documented as broken on NFS. if use a static suffix - i.e.
> > filename + '.bzrtmp', if someone has a file that looks like that,  
> > we may
> > overwrite it unintentionally - *depending on the manner of the
> > brokenness for NFS*.
> 
> But you may overwrite something called foo.$pid.tmp too. ??
> 
> > If its 'race conditions with two clients writing the same file'  
> > broken -
> > then I'm happy to remove the pid. If its 'O_EXCL is simply ignored on
> > some implementations' then I think the pid is a not-too-bad price to
> > pay.
> 
> I think your patch had the problem that if the file happens to exist  
> (e.g. a previous run crashed) then the open will fail, which would be  
> unfortunate.  Including the pid makes it less likely but it can still  
> happen.  So you do need to catch that case, and I would suggest just  
> retrying.
> 
> On local filesystems, O_EXCL will be safe.  On NFS, even including  
> the pid is not enough (and I don't think the atomic rename is  
> guaranteed either).  So I don't see what the pid really gains you.

I'm happy to pull it out - I think you put it in in the first place ;).
I agree with that bug condition, I'll add a fix for that before
resubmitting.

> > And thread safety may be an issue too. I think calculating the umask
> > when the module is first used, and then chmodding IFF its needed is a
> > reasonable compromise.
> 
> That's OK with me.

Cool.

Rob
-- 
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