Provides several thread-safe collection classes that should be used in place of the corresponding types in the System.Collections.NonGeneric and System.Collections packages whenever multiple threads are accessing the collection concurrently. Commonly Used Types: System.Collections.Concurrent.ConcurrentDictionary<TKey, TValue> System.Collections.Concurrent.ConcurrentQueue<T> System.Collections.Concurrent.ConcurrentBag<T> System.Collections.Concurrent.BlockingCollection<T> System.Collections.Concurrent.ConcurrentStack<T> When using NuGet 3.x this package requires at least version 3.4.