Since I'm looking at mono addins as a mechanism for managing 3rd party
packages for OpenSim, I couldn't help it but also look at the way mono
addins are being used within OpenSim. It is very confusing, with
extension points being declared on components that have very little to
do with the extensions. For example, OpenSim.exe itself defines 3
extension points:
<ExtensionPoint path="/OpenSim/Startup">
<ExtensionNode name="Plugin"
type="OpenSim.Framework.PluginExtensionNode"
objectType="OpenSim.IApplicationPlugin"/>
</ExtensionPoint>
<ExtensionPoint path="/OpenSim/WindModule" name="Wind Module
Plugins for wind models">
<ExtensionNode name="WindModel"
type="Mono.Addins.TypeExtensionNode"
objectType="OpenSim.Region.Framework.Interfaces.IWindModelPlugin"/>
</ExtensionPoint>
<ExtensionPoint path="/OpenSim/RegionModules">
<ExtensionNode name="RegionModule"
type="Mono.Addins.TypeExtensionNode"
objectType="OpenSim.Region.Framework.Interfaces.IRegionModuleBase"/>
</ExtensionPoint>
While the first one is a genuine extension point of OpenSim.exe (the
object type is defined in it), the other two aren't. Both the WindModule
and the RegionModules extension points pertain to types that are defined
in OpenSim.Region.Framework.dll. In the code, as well as in intention,
these are extensions of OpenSim.Region.Framework. When we add region
modules, the main dependency is, indeed, that dll, and it's also the dll
that most affects the stability of 3rd party region modules. The future
API for region modules will pertain primarily to this dll. So this is
the right dll for defining the extension point for region modules.
OpenSim has an intermediate component for loading and activating region
modules, the RegionModuleControllerPlugin, which happens to be an
extension of /OpenSim/Startup. If anyone cares to do it, it is possible
to disable the current
RegionModuleControllerPlugin and plugin another one instead that manages
region modules differently. I don't see a reason for doing that, and
honestly I don't see a reason for RegionModuleControllerPlugin to be an
addin in the first place. But that's what it is, and I don't plan to
change it. But it adds a layer of confusion about addins in OpenSim that
I believe is what what led to the current situation of hanging those 2
extension points from OpenSim.exe.
I really want to fix the broken conceptual model of hanging
/OpenSim/RegionModules and /OpenSim/WindModule out of OpenSim.exe. They
belong in OpenSim.Region.Framework.
I have made local changes in my repo that fix this, and it all works
correctly. However, this implies that everyone who develops region
modules will need to change the dependency of their region module dlls
from the mysterious
[assembly: AddinDependency("OpenSim", "0.5")]
to
[assembly: AddinDependency("OpenSim.Region.Framework", "0.8.1")] (or
whatever version)
Also version numbers will change meaningfully from here on.
This change is trivial -- a global replace will do it.
I have this ready to be pushed, but wanted to give an opportunity for
discussion before I do it.
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