[Opensim-dev] Mega Regions and PAL support in OpenSim?

[Teravus Ovares]

Taints are there because many threads modify the properties of
physicsactors.     The properties are also not inherently thread safe.
   So, to ensure data integrity, you can lock the internal data types
when setting them, or you can keep a list of tainted physics actors
and send the changed values to the internal physics engine within the
thread context of region's heartbeat thread.    This is especially
important when dealing with unmanaged resources.  For example, with
the OpenDynamicsEngine physics plugin, if the internal data was set by
the properties directly, the server would quickly crash with a memory
access violation or assert with, 'invalid operation for locked space;.

So, what I do, generally, is maintain a plugin state and an internal
physics engine state for each physics actor.    The region, when
setting one of the properties, will taint physics actors by calling
the method in the PhysicsScene with the Physics Actor that it tainted.
  The next time the heartbeat thread steps the physics world, just
before stepping the world and doing collision detection, the plugin
state gets locked and applied to the internal physics engine.   This
strategy keeps locking to a minimum while allowing multiple threads to
change the state safely.

Regards

Teravus

On Wed, Sep 30, 2009 at 9:35 PM, Robert A. Knop Jr. <rknop at pobox.com> wrote:
> On Wed, Sep 30, 2009 at 06:23:56PM -0700, Dahlia Trimble wrote:
>> We're watching PAL and may consider it when we find it to be sufficient for
>> use with OpenSim. Another factor to consider is the majority of OpenSim
>> developers are unpaid volunteers and it's difficult to find people who have
>> the knowledge and expertise for implementing physics simulations and are
>> willing to donate their time and services. If you have this expertise or
>> know of someone else who would be willing to help implement PAL then please
>> do consider creating a PAL module and donating it to the community.
>
> I fully understand (at this point) the MICASim Physics module and how it
> interacts; thanks to ter_afk (on IRC-- I wish I knew his real name!) for
> some pointers on getting the message back that the scene needs to get
> updated info from the physics sim.
>
> I have figured out a bunch of what needs to happen, but not all of it.
> Could somebody point me to where I'd look to understand what taints are
> all about WRT a physics engine?
>
> I have various interests in physics engines, what with being a
> physicist and the last one to hack the MICA code....
>
> --
> --Rob Knop
>  E-mail:    rknop at pobox.com
>  Home Page: http://www.pobox.com/~rknop/
>  Blog:      http://www.sonic.net/~rknop/blog/
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