ConcurrentRequestQueue - Always see queue as empty after having reach…

…ed RequestLimit
NLog · May 26, 2019 · 09c087f · 09c087f
1 parent b83d37f
commit 09c087f
Showing 1 changed file with 9 additions and 10 deletions.
diff --git a/src/NLog/Targets/Wrappers/ConcurrentRequestQueue.cs b/src/NLog/Targets/Wrappers/ConcurrentRequestQueue.cs
@@ -79,6 +79,7 @@ public ConcurrentRequestQueue(int requestLimit, AsyncTargetWrapperOverflowAction
         public override bool Enqueue(AsyncLogEventInfo logEventInfo)
         {
             long currentCount = Interlocked.Increment(ref _count);
+            bool queueWasEmpty = currentCount == 1;  // Inserted first item in empty queue
             if (currentCount > RequestLimit)
             {
                 InternalLogger.Debug("Async queue is full");
@@ -91,18 +92,19 @@ public override bool Enqueue(AsyncLogEventInfo logEventInfo)
                                 if (_logEventInfoQueue.TryDequeue(out var lostItem))
                                 {
                                     InternalLogger.Debug("Discarding one element from queue");
-                                    currentCount = Interlocked.Decrement(ref _count);
+                                    queueWasEmpty = Interlocked.Decrement(ref _count) == 1;
                                     OnLogEventDropped(lostItem.LogEvent);
                                     break;
                                 }
-                                Interlocked.Decrement(ref _count);
-                                currentCount = Interlocked.Increment(ref _count);
+                                currentCount = Interlocked.Read(ref _count);
+                                queueWasEmpty = true;
                             } while (currentCount > RequestLimit);
                         }
                         break;
                     case AsyncTargetWrapperOverflowAction.Block:
                         {
-                            currentCount = WaitForBelowRequestLimit();
+                            WaitForBelowRequestLimit();
+                            queueWasEmpty = true;
                         }
                         break;
                     case AsyncTargetWrapperOverflowAction.Grow:
@@ -115,10 +117,10 @@ public override bool Enqueue(AsyncLogEventInfo logEventInfo)
                 }
             }
             _logEventInfoQueue.Enqueue(logEventInfo);
-            return currentCount == 1;    // Inserted first item in empty queue
+            return queueWasEmpty;
         }
 
-        private long WaitForBelowRequestLimit()
+        private void WaitForBelowRequestLimit()
         {
             long currentCount;
             bool lockTaken = false;
@@ -130,24 +132,21 @@ private long WaitForBelowRequestLimit()
                 // If yield did not help, then wait on a lock
                 while (currentCount > RequestLimit)
                 {
-                    Interlocked.Decrement(ref _count);
                     InternalLogger.Debug("Blocking because the overflow action is Block...");
                     if (!lockTaken)
                         Monitor.Enter(_logEventInfoQueue);
                     else
                         Monitor.Wait(_logEventInfoQueue);
                     lockTaken = true;
                     InternalLogger.Trace("Entered critical section.");
-                    currentCount = Interlocked.Increment(ref _count);
+                    currentCount = Interlocked.Read(ref _count);
                 }
             }
             finally
             {
                 if (lockTaken)
                     Monitor.Exit(_logEventInfoQueue);
             }
-
-            return currentCount;
         }
 
         private long TrySpinWaitForLowerCount()