ConcurrencyAbstractionLayerImpl.Timer: Allow delegate caching.

Rx.NET/Source/src/System.Reactive/Concurrency/ConcurrencyAbstractionLayerImpl.cs

@@ -132,35 +132,39 @@ public void StartThread(Action<object> action, object state)
 
         private sealed class Timer : IDisposable
         {
+            private object _state;
             private Action<object> _action;
             private volatile System.Threading.Timer _timer;
 
             public Timer(Action<object> action, object state, TimeSpan dueTime)
             {
+                _state = state;
                 _action = action;
 
                 // Don't want the spin wait in Tick to get stuck if this thread gets aborted.
                 try { }
                 finally
                 {
                     //
-                    // Rooting of the timer happens through the this.Tick delegate's target object,
+                    // Rooting of the timer happens through the Timer's state
                     // which is the current instance and has a field to store the Timer instance.
                     //
-                    _timer = new System.Threading.Timer(Tick, state, dueTime, TimeSpan.FromMilliseconds(System.Threading.Timeout.Infinite));
+                    _timer = new System.Threading.Timer(_ => Tick(_), this, dueTime, TimeSpan.FromMilliseconds(System.Threading.Timeout.Infinite));
                 }
             }
 
-            private void Tick(object state)
+            private static void Tick(object state)
             {
+                var timer = (Timer) state;
+
                 try
                 {
-                    _action(state);
+                    timer._action(timer._state);
                 }
                 finally
                 {
-                    SpinWait.SpinUntil(IsTimerAssigned);
-                    Dispose();
+                    SpinWait.SpinUntil(timer.IsTimerAssigned);
+                    timer.Dispose();
                 }
             }
 
@@ -173,6 +177,7 @@ public void Dispose()
                 {
                     _action = Stubs<object>.Ignore;
                     _timer = TimerStubs.Never;
+                    _state = null;
 
                     timer.Dispose();
                 }