Clear buffers under lock (#526)

Author: bitfaster

BitFaster.Caching/Buffers/MpscBoundedBuffer.cs

@@ -254,6 +254,9 @@ private static int Length(Span<T> output)
         /// <summary>
         /// Removes all values from the buffer.
         /// </summary>
+        /// <remarks>
+        /// Clear must be called from the single consumer thread.
+        /// </remarks>
         public void Clear()
         {
             while (TryTake(out _) != BufferStatus.Empty)

BitFaster.Caching/Buffers/StripedMpscBuffer.cs

@@ -123,7 +123,7 @@ public BufferStatus TryAdd(T item)
         /// Removes all values from the buffer.
         /// </summary>
         /// <remarks>
-        /// Not thread safe.
+        /// Clear must be called from the single consumer thread.
         /// </remarks>
         public void Clear()
         {

BitFaster.Caching/Lfu/ConcurrentLfuCore.cs

@@ -137,11 +137,10 @@ public void Clear()
         {
             this.Trim(this.Count);
 
-            this.readBuffer.Clear();
-            this.writeBuffer.Clear();
-
             lock (maintenanceLock)
             {
+                this.readBuffer.Clear();
+                this.writeBuffer.Clear();
                 this.cmSketch.Clear();
             }
         }