[SharedArrayPool](https://github.com/dotnet/runtime/blob/50be35a211536209b3e1d68619f7d2f2bf3caa0a/src/libraries/System.Private.CoreLib/src/System/Buffers/SharedArrayPool.cs#L28) uses `ThreadStatic`, while `DefaultArrayPool` uses [SpinLock](https://github.com/dotnet/maintenance-packages/blob/main/src/System.Buffers/src/System/Buffers/DefaultArrayPoolBucket.cs#L26).
