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Re: [Duplicity-talk] Re: Re: Can one safely run multiple instances tothe


From: Peter Schuller
Subject: Re: [Duplicity-talk] Re: Re: Can one safely run multiple instances tothesame target?
Date: Tue, 18 Mar 2008 16:09:33 +0100
User-agent: Mutt/1.5.17 (2007-11-01)

> I'm not entirely sure.  One thing that one could conceivably do is something 
> like "heartbeat" file whose timestamp is updated every XXX seconds.  If you 
> set duplicity to produce a 5s heartbeat, a second instance would expect to 
> see that file's timestamp be modified within 5 seconds.  If not, then the 
> original duplicity likely failed.  Obviously, this is a very basic concept 
> that I'm describing; I'd probably have the second instance wait a factor of 
> the heartbeat timeout before it were to determine that the lock was stale. 
> Of course, this would imply 2 simultaneous connections from duplicity to the 
> backend; one to upload the file, and one to keep the heartbeat updated.  I 
> don't know how easy it is to develop multi-threaded things in python ... i'm 
> just brainstorming a little.

My mkdir() lock was actually meant to be local, rather than on the
backend. While a lock on the actual backend would be useful, that is
going to be more problematic to do portably. It is also likely to
cause a very high amount of false positives in many situations, as any
failures due to communication will generate stale files. With a local
lock, only harder local crashes would cause false positives.

-- 
/ Peter Schuller

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