restored volatile, cache value before comparand

src/core/Akka/Actor/Scheduler/HashedWheelTimerScheduler.cs

@@ -114,7 +114,7 @@ public HashedWheelTimerScheduler(Config scheduler, ILoggingAdapter log) : base(s
         /// <summary>
         /// 0 - init, 1 - started, 2 - shutdown
         /// </summary>
-        private int _workerState = WORKER_STATE_INIT;
+        private volatile int _workerState = WORKER_STATE_INIT;
 
         private static Bucket[] CreateWheel(int ticksPerWheel, ILoggingAdapter log)
         {
@@ -147,25 +147,27 @@ private static int NormalizeTicksPerWheel(int ticksPerWheel)
 
         private void Start()
         {
-            if (_workerState == WORKER_STATE_STARTED)
+            // only read the worker state once so it can't be a moving target for else-branch
+            var workerStateRead = _workerState;
+            if (workerStateRead == WORKER_STATE_STARTED)
             {
                 // do nothing
             }
-            else if (_workerState == WORKER_STATE_INIT)
+            else if (workerStateRead == WORKER_STATE_INIT)
             {
                 if (Interlocked.CompareExchange(ref _workerState, WORKER_STATE_STARTED, WORKER_STATE_INIT) == WORKER_STATE_INIT)
                 {
                     _timer ??= new PeriodicTimer(_timerDuration);
-                    Task.Run(() => RunAsync(_cts.Token)); // start the clock
+                    Task.Run(() => RunAsync(_cts.Token).ConfigureAwait(false)); // start the clock
                 }
             }
-            else if (_workerState == WORKER_STATE_SHUTDOWN)
+            else if (workerStateRead == WORKER_STATE_SHUTDOWN)
             {
                 throw new SchedulerException("cannot enqueue after timer shutdown");
             }
             else
             {
-                throw new InvalidOperationException($"Worker in invalid state: {_workerState}");
+                throw new InvalidOperationException($"Worker in invalid state: {workerStateRead}");
             }
 
             if(_startTime == 0)