ReaderWriterLockSlim .NET v3.5
Via this post.
ReaderWriterLock is used in .NET Framework in order to make synchronizations between threads to ensure thread-safety and atomic operations.
.NET v3.5 introduces a new version of this object - ReaderWriterLockSlim
The "slim" version is supposed to improve performance significantly, so if you need such locking behavior, the suggestion is - use this one.
Do note that replacing existing code will result in breaking changes -
"AcquireWriterLock becomes EnterWriterLock (or TryEnterWriterLock) for example."