Description of problem:

Using classLoader="instance" in plugin descriptors cause problems when starting an agent clean when there are resources in inventory that need to be synced to the agent. In this case, multiple resource classloaders are created for a single resource and things go haywire - culminating in things like "ClassCastException" for what seems like correct casting.

How reproducible:

Commit to inventory a resource that needs an instance classlaoder. Get the agent fully synced and ensure it works and things are fine. Then, shutdown the agent and restart it using --cleanconfig. You may notice (unsure if it happens all the time, probably depends on the code) that you will get odd class errors like ClassCastException for what looks like a safe cast.

Analysis:

InventoryManager.mergeResourceFromDiscovery is getting called before the agent syncs with the server. In this case, there are no resource containers in the inventory manager for known, committed resources in inventory. Therefore, when that method calls "findMatchingChildResource" to see if the resource exists (via "match" method), nothing will be found and it will create a resource classloader for it, associating that CL with the discovered "uuid" which is NOT going to be the UUID of the resource in inventory. The discovery component therefore will load in some classes in that classloader.

Then after the sync happens, the resource container is associated with the "real" resource with the "real" UUID. The resource component getting called for the first time requires a new classloader because the UUID is different (ClassLoaderManager keys on UUID) and creates a new CL. The component tries to use that classloader but is operating on classes loaded by the first CL that was created and bad things happen.

I don't know how to fix this yet - I think the ClassLoaderManager needs to do some tricks to know that a previous classloader should be reused. We can't use UUID as the key - there has to be some other identifier that is the same for both newly discovered resources and resources that are in inventory. Some relationship with resourceKey and parent resourceKey perhaps??