https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.synchronizedkeyedcollection-2?view=netframework-4.8.1&redirectedfrom=MSDN
SynchronizedKeyedCollectionK,T Class (System.Collections.Generic) | Microsoft Learn
Provides a thread-safe collection that contains objects of a type specified by a generic parameter and that are grouped by keys.
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