ComWrappers.GetOrCreateObjectForComInstance becomes expensive during the Get cached RCW scenario when called from multiple threads

[manodasanW]

Description

From multiple different threads, do calls to ComWrappers.GetOrCreateObjectForComInstance to get the RCW for the same existing native object which has already been cached. Observe that the amount of time this takes can be pretty high due to the mutex in ExtObjCxtCache which causes it to become a one at a time operation to do the cached RCW lookup.

runtime/src/coreclr/vm/interoplibinterface_comwrappers.cpp

Line 828 in 7cffd46

ExtObjCxtCache::LockHolder lock(cache);

Configuration

.NET 6

Regression?

No

[AaronRobinsonMSFT]

The fix here would be to use a reader/writer lock instead of a mutex. We should consider this early in .NET 9.

/cc @agocke @jkoritzinsky