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List:       opensim-dev
Subject:    [Opensim-dev] SceneGraph data access refactoring
From:       dan.lake () intel ! com (Lake, Dan)
Date:       2010-03-19 13:19:16
Message-ID: 1DEA2A500941AD41AF9F9A712451BD805C306B29 () orsmsx502 ! amr ! corp ! intel ! com
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Based on feedback, I am putting in an updated patch this morning on the scene \
presence access refactoring.

1. Scene.GetScenePresence() will stay with the caveat that the caller must check for \
null. It's my understanding that this is the pattern preferred by core. There is a \
variant for UUID, localID and first/last name. 

2. TryGetAvatar() will also remain on SceneManager, SceneBase, Scene and SceneGraph \
but has been renamed TryGetScenePresence(UUID) since that is what it does and returns \
a boolean. The same variants exist as for GetScenePresence. (Note: If this is \
non-prefered then it can be removed unless there is a technical reason that it must \
stay. The TryGet pattern is used in places for other data such as appearance also.)

3. GetAvatars() and GetScenePresences() have been removed from Scene. To iterate over \
presences, pass a delegate to Scene.ForEachScenePresence().

Dan lake
Intel Labs
dan.lake at intel.com


From: opensim-dev-bounces@lists.berlios.de [mailto:opensim-dev-bounces at \
                lists.berlios.de] On Behalf Of Lake, Dan
Sent: Thursday, March 18, 2010 4:38 PM
To: opensim-dev at lists.berlios.de
Subject: [Opensim-dev] SceneGraph data access refactoring

I am committing a set of patches this week which make data access and locking of \
presences within the scene graph more consistent. There are currently many ways to \
get presence data from the scene graph and/or iterate over it. To name a few, there \
are GetScenePresence, TryGetAvatar, GetScenePresences and ForEachScenePresence.? \
Unfortunately, some of these have relied on the callers locking the list or checking \
for null references which was missing in many places.

The patches move all locking into SceneGraph, eliminate GetScenePresence in favor of \
TryGetAvatar, and consolidates the two different presence iteration patterns. Instead \
of calling GetScenePresences() and iterating over the result, modules and other code \
should call ForEachScenePresence(Action<ScenePresence>) and let SceneGraph do the \
parallel work. Eventually this will also mean that the list does not need to be \
copied or locked in order to iterate since it changes infrequently but is iterated my \
many callers simultaneously.

The goal is to move SceneGraph toward a self-supporting container of entities with \
properties and a small lightweight interface for adding, removing, and performing \
actions on the container through the use of properties/components, filters, and \
delegates. Supporting or allowing a module to grab a reference to the internal array \
of presences and lock it so that no other thread may add/remove/iterate is seriously \
limiting scalability and has introduced reliability issues and races between the \
scene and some modules.

Dan lake
Intel Labs
dan.lake at intel.com


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