# System.Threading

``` diff
 namespace System.Threading {
     public sealed class PreAllocatedOverlapped : IDisposable {
+        ~PreAllocatedOverlapped();
     }
     public sealed class ReaderWriterLock : CriticalFinalizerObject {
-        ~ReaderWriterLock();

     }
     public sealed class Timer : MarshalByRefObject, IAsyncDisposable, IDisposable {
+        public static long ActiveCount { get; }
     }
 }
```

