[Opensim-dev] Lockless Lists?

[Justin Clark-Casey]

Frisby, Adam wrote:
> I’ve managed to get the majority of my goals solved here without 
> removing the locks – but by making a new EntityManager to deal with 
> those locks.
> 
>  
> 
> Code has been checked in tonight as it doesn’t look like it should cause 
> any new issues. May improve performance during login/logout – but 
> ScenePresences (which I haven’t touched yet) is probably the real 
> culprit there.

To be honest, I suspect the real issue on login/logout performance is the fact that mono does not yet implement thread 
prioritization - you can see it but properties such as Thread.Priority are merely stubs.

So when a login/logout comes along it's not currently possible to give existing clients or threads such as the scene 
update execution priority.  So I'm thinking that the significant cpu spike on login/logout slows the whole system down.

I looked at login recently and I don't believe that the periods of lock holding are significant enough to be causing the 
delay.

No actual proper performance analysis was carried out so I could be wrong.

> 
>  
> 
> Adam
> 
>  
> 
> *From:* opensim-dev-bounces at lists.berlios.de 
> [mailto:opensim-dev-bounces at lists.berlios.de] *On Behalf Of *Lc
> *Sent:* Monday, 24 November 2008 2:39 AM
> *To:* opensim-dev at lists.berlios.de
> *Subject:* Re: [Opensim-dev] Lockless Lists?
> 
>  
> 
> fine but could we tag a "stable" release before ?
> SM
> 
> On Mon, Nov 24, 2008 at 11:23 AM, Frisby, Adam <adam at deepthink.com.au 
> <mailto:adam at deepthink.com.au>> wrote:
> 
> I've recently discovered (and perhaps I should have known this earlier) 
> it's possible to create a reasonably high performance lock-free 
> list/dictionary/stack/queue structure under C#.
> 
>  
> 
> Julian Bucknall has posted the sourcecode to a bunch of these here: 
> http://www.boyet.com/articles/lockfreestack.html
> 
>  
> 
> One of the big performance issues with OpenSim is our overreliance on 
> locking data structures, which can cause issues when those locks don't 
> release in a timely manner. If we switched to lockless structures – we 
> could effectively eliminate those issues. (and probably create new ones.)
> 
>  
> 
> Does anyone have any opposition if we try to replace some of the core 
> structures with lock-free versions, and then removing the locks on them? 
> I'm thinking Scene.Entities, Scene.Presences would be two good targets 
> for the first lot, then maybe we can attack some deeper bits later.
> 
>  
> 
> Adam
> 
> 
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Justin Clark-Casey
http://justincc.wordpress.com