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From Felix Meschberger <fmesc...@gmail.com>
Subject Re: [jr3] Synchronized sessions
Date Thu, 25 Feb 2010 15:56:29 GMT
Hi,

On 25.02.2010 16:33, Thomas Müller wrote:
> Hi,
> 
>> this creates a big potential for deadlocks
> 
> Could you provide an example on how such a deadlock could look like?

I don't have an example off hand, and as Jukka said, it might well be,
that there might be none. Still the potential exists, especially if the
session is not fully synchronized...

> 
>> just synchronizing all methods
>> So you also synchronize all Node/Item/Property methods
> 
> Some methods don't need to be synchronized, for example some getter
> methods such as Session.getRepository(), RangeIterator.getPosition()
> and getSize(). I'm not sure if Node.getProperty needs to be
> synchronized. The Value class is (almost) immutable so synchronization
> is not required here. But very likely Session.getNode(..) and
> Node.getNode() need to be synchronized because those potentially
> modify the cache.
> 
>> ensure that for a given Item x, the same Item instance is always returned from all
getXXX methods ....
> 
> I'm not sure what you are referring to. Jackrabbit already does ensure
> the same node object is returned as far as I know, but for other
> reasons than synchronization.
> 
>> if people do the wrong things, well, fine, let them do ...
> 
> It's usually not those people that have to fix broken repositories.
> 
>> my veto
> 
> Let's see.

;-)


Regards
Felix

> 
>> Most jcr apps I've seen often use a single session from several threads to read from
this session. (I think I also read it somewhere that this is safe with jackrabbit, but I might
be mistaken).
> 
> I'm not sure if this is really safe. Maybe it is problematic if one
> thread uses the same session for updates.
> 
>> Simply syncing everything on the session would decrease performance in these cases
dramatically.
> 
> Actually, I don't think that's the case.
> 
> Regards,
> Thomas
> 


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