Search for opportunities to use Dictionary.Remove while enumerating without defensive copy

[roji]

.NET Core 3.0 added the possibility to safely remove entries from Dictionary while enumerating (dotnet/coreclr#18854). We may have places where we copy defensively because this scenario was not previously supported - we may be able to remove these copies for better perf.

[michalczerwinski]

I this something I can help with?

Sample finding:

RemoveDerivedEntityTypes.cs, line 240:

            foreach (var entityType in entityTypeDictionary.Where(e => e.Key.BaseType != null))
            {
                foreach (var otherEntityType in entityTypesWithDerivedTypes)
                {
                    if (toRemove.Contains(otherEntityType)
                        || otherEntityType.Equals(entityType))
                    {
                        continue;
                    }

                    if (otherEntityType.Key.IsAssignableFrom(entityType.Key))
                    {
                        toRemove.Add(entityType);
                        break;
                    }
                }
            }

            foreach (var entityType in toRemove)
            {
                entityTypeDictionary.Remove(entityType.Key);
            }

No need for toRemove collection, we can just simply remove in the main loop..

I think I managed to find all potential places for this change:

Also, in some cases we may want to use something along the lines of EnumerateForRemoval.

[roji]

@michalczerwinski I think this is in TableSharingConcurrencyTokenConvention.cs, not RemoveDerivedEntityTypes.cs, no?

Yes, this does seem like a candidate for simplification/optimization. Note that it's only possible to reliably do this where we're handling a concrete Dictionary (as opposed to IDictionary).

[michalczerwinski]

I thoroughly verified all cases and ended up with #24814
Not much, I know. Please let me know if you can see more potential patterns.