[Opensim-dev] Dynamic attributes

Thu Feb 7 02:11:37 UTC 2013

On 06/02/13 21:58, Mic Bowman wrote:
> Justin,
>
> I took a look at the DAMap data structure & have some questions. What's the value of explicit methods for the top level
> of the structure? It is still possible to have name space collisions since there is nothing that prevents one module
> from writing into another module's "name space". Also, whats your expectation for locking? The top level accessor locks
> the structure, but modules that share the rest of the structure will have to do their own locking anyway. I guess one
> value of controlling the top level is that *IF* modules are making exclusive access to the structure, the locking is
> minimized. Hard to control that, though.

The idea was to separate out DAMap into 'namespaces' (over-reaching name I know) so that distributed users did not 
casually overwite each other's data by writing directly to a root OSDMap.  Thus, moduleA would always write to a map 
under the name "modA" and moduleB under the name "modB" and never the twain would meet.

This doesn't stop modules from deliberately overwriting or deleting each other's data.  But if you really wanted to do 
that you could always achieve it by directly fiddling with the XML serialization.  At least this way, somebody writing a 
module just by experimenting with methods rather than reading doc (which is how most people do it, myself included if 
I'm being honest) will not casually overwrite the properties of another storer.

You're right about the deficient locking story.  At the moment, any module changing its OSDMap directly needs to lock 
DAMap, and even DAExampleModule doesn't do this.

But really, it would be better to lock the individual 'namespace' maps for better granularity.  I may make this change 
if there is no further discussion on this point.

I also think that we need to know what will happen if a module forgets to lock and serialization occurs concurrently 
with a map change.  What we cannot do is write corrupt XML to the SOP serialization.

>
> Did you get a chance to look at the JsonStore structure? The path-based accessors are very different than providing
> immediate access to the OSDMap. As we discussed, I made that decision to support the synchronization operations (take &
> read) and it removes the exposed OSDMap so that the data structure can be replaced. I think the path-based accessor is
> probably too heavyweight for DAMap... well... maybe... given that we dont have any examples yet its hard to tell. :-)

Yeah, I really do need to take a closer look.  Will try and do that soon, hopefully Fri.

>
> --mic
>
>
> On Mon, Feb 4, 2013 at 5:09 PM, Justin Clark-Casey <jjustincc at googlemail.com <mailto:jjustincc at googlemail.com>> wrote:
>
>     Okay, I have now merged this branch (dynamic-attributes2) to master.  Please report any problems (or fix them :)
>
>     As this is experimental functionality, if necessary it can be changed/bug-fixed without any attempt to preserve
>     existing data.  Any code using it should handle the 'expected data not found' case anyway.
>
>     On 26/01/13 19:52, Adams, Robert wrote:
>
>         This implementation will work for physics. The physics engine cannot reference Scene (circular reference
>         madness) so, on creation of the scene's physics instance, I will pass in the instance of DAMap (since it is
>         defined in OpenSim.Framework) much the same way the asset request method instance is passed in.
>
>         I am +2 on this branch's inclusion into master.
>
>         -- ra
>
>         -----Original Message-----
>         From: opensim-dev-bounces at lists.__berlios.de <mailto:opensim-dev-bounces at lists.berlios.de>
>         [mailto:opensim-dev-bounces at __lists.berlios.de <mailto:opensim-dev-bounces at lists.berlios.de>] On Behalf Of
>         Justin Clark-Casey
>         Sent: Friday, January 25, 2013 5:14 PM
>         To: opensim-dev at lists.berlios.de <mailto:opensim-dev at lists.berlios.de>
>         Subject: Re: [Opensim-dev] Dynamic attributes
>
>         On 25/01/13 08:40, Oren Hurvitz wrote:
>
>             Ok, great. I hope all goes well and this will be added to master soon.
>
>             What do you mean by "put the code in for MSSQL"? The code already
>             supports MySQL, MSSQL and SQLite.
>
>
>         Apologies - my brain stored the assumption that only MySQL had been added since that's the only one I remembered
>         seeing in the commit summaries but I see that the MSSQL code is there.
>
>         --
>         Justin Clark-Casey (justincc)
>         OSVW Consulting
>         http://justincc.org
>         http://twitter.com/justincc
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>
>     --
>     Justin Clark-Casey (justincc)
>     OSVW Consulting
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>     http://twitter.com/justincc
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-- 
Justin Clark-Casey (justincc)
OSVW Consulting
http://justincc.org
http://twitter.com/justincc