Make buffer Clear() thread safe (#523)

Author: bitfaster

BitFaster.Caching/Buffers/MpmcBoundedBuffer.cs

@@ -12,7 +12,7 @@ namespace BitFaster.Caching.Buffers
     /// Based on the Segment internal class from the .NET ConcurrentQueue class.
     public sealed class MpmcBoundedBuffer<T>
     {
-        private Slot[] slots;
+        private readonly Slot[] slots;
         private readonly int slotsMask;
         private PaddedHeadAndTail headAndTail; // mutable struct, don't mark readonly
 
@@ -208,13 +208,11 @@ public BufferStatus TryAdd(T item)
         /// <summary>
         /// Removes all values from the buffer.
         /// </summary>
-        /// <remarks>
-        /// Not thread safe.
-        /// </remarks>
         public void Clear()
         {
-            slots = new Slot[slots.Length];
-            headAndTail = new PaddedHeadAndTail();
+            while (TryTake(out _) != BufferStatus.Empty)
+            { 
+            }
         }
 
         [StructLayout(LayoutKind.Auto)]

BitFaster.Caching/Buffers/MpscBoundedBuffer.cs

@@ -13,7 +13,7 @@ namespace BitFaster.Caching.Buffers
     [DebuggerDisplay("Count = {Count}/{Capacity}")]
     public sealed class MpscBoundedBuffer<T> where T : class
     {
-        private T[] buffer;
+        private readonly T[] buffer;
         private readonly int mask;
         private PaddedHeadAndTail headAndTail; // mutable struct, don't mark readonly
 
@@ -254,13 +254,11 @@ private static int Length(Span<T> output)
         /// <summary>
         /// Removes all values from the buffer.
         /// </summary>
-        /// <remarks>
-        /// Not thread safe.
-        /// </remarks>
         public void Clear()
         {
-            buffer = new T[buffer.Length];
-            headAndTail = new PaddedHeadAndTail();
+            while (TryTake(out _) != BufferStatus.Empty)
+            {
+            }
         }
     }
 }

BitFaster.Caching/Lfu/ConcurrentLfuCore.cs

@@ -137,11 +137,12 @@ public void Clear()
         {
             this.Trim(this.Count);
 
+            this.readBuffer.Clear();
+            this.writeBuffer.Clear();
+
             lock (maintenanceLock)
             {
                 this.cmSketch.Clear();
-                this.readBuffer.Clear();
-                this.writeBuffer.Clear();
             }
         }