Eliminate races during LRU warmup (#457)

Author: bitfaster

BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs

@@ -562,11 +562,10 @@ public void WhenValueExpiresItIsDisposed()
                 lruOfDisposable.GetOrAdd(i, disposableValueFactory.Create);
             }
 
-            disposableValueFactory.Items[0].IsDisposed.Should().BeFalse();
-            disposableValueFactory.Items[1].IsDisposed.Should().BeFalse();
-
-            disposableValueFactory.Items[2].IsDisposed.Should().BeTrue();
+            disposableValueFactory.Items[0].IsDisposed.Should().BeTrue();
 
+            disposableValueFactory.Items[1].IsDisposed.Should().BeFalse();
+            disposableValueFactory.Items[2].IsDisposed.Should().BeFalse();
             disposableValueFactory.Items[3].IsDisposed.Should().BeFalse();
             disposableValueFactory.Items[4].IsDisposed.Should().BeFalse();
             disposableValueFactory.Items[5].IsDisposed.Should().BeFalse();
@@ -598,8 +597,8 @@ public void WhenValueEvictedItemRemovedEventIsFired()
 
             removedItems.Count.Should().Be(2);
 
-            removedItems[0].Key.Should().Be(3);
-            removedItems[0].Value.Should().Be(4);
+            removedItems[0].Key.Should().Be(1);
+            removedItems[0].Value.Should().Be(2);
             removedItems[0].Reason.Should().Be(ItemRemovedReason.Evicted);
 
             removedItems[1].Key.Should().Be(4);
@@ -1016,6 +1015,8 @@ public void WhenTrimCountIsMoreThanCapacityThrows()
         [InlineData(9, new int[] { })]
         public void WhenColdItemsExistTrimRemovesExpectedItemCount(int trimCount, int[] expected)
         {
+            Warmup();
+
             // initial state:
             // Hot = 9, 8, 7
             // Warm = 3, 2, 1
@@ -1109,6 +1110,8 @@ public void WhenHotItemsExistTrimRemovesExpectedItemCount(int itemCount, int[] e
         [InlineData(9, new int[] { })]
         public void WhenColdItemsAreTouchedTrimRemovesExpectedItemCount(int trimCount, int[] expected)
         {
+            Warmup();
+
             // initial state:
             // Hot = 9, 8, 7
             // Warm = 3, 2, 1

BitFaster.Caching.UnitTests/Lru/ConcurrentTLruTests.cs

@@ -92,8 +92,8 @@ public void WhenValueEvictedItemRemovedEventIsFired()
 
             removedItems.Count.Should().Be(2);
 
-            removedItems[0].Key.Should().Be(3);
-            removedItems[0].Value.Should().Be(4);
+            removedItems[0].Key.Should().Be(1);
+            removedItems[0].Value.Should().Be(2);
             removedItems[0].Reason.Should().Be(ItemRemovedReason.Evicted);
 
             removedItems[1].Key.Should().Be(4);

BitFaster.Caching/Lru/ConcurrentLruCore.cs

@@ -587,20 +587,14 @@ private void CycleDuringWarmup(int hotCount)
 
                 if (this.hotQueue.TryDequeue(out var item))
                 {
-                    // always move to warm until it is full
-                    if (Volatile.Read(ref this.counter.warm) < this.capacity.Warm)
-                    {
-                        // If there is a race, we will potentially add multiple items to warm. Guard by cycling the queue.
-                        int warmCount = this.Move(item, ItemDestination.Warm, ItemRemovedReason.Evicted);
-                        CycleWarm(warmCount);
-                    }
-                    else
+                    int count = this.Move(item, ItemDestination.Warm, ItemRemovedReason.Evicted);
+
+                    // if warm is now full, overflow to cold and mark as warm
+                    if (count > this.capacity.Warm)
                     {
-                        // Else mark isWarm and move items to cold.
-                        // If there is a race, we will potentially add multiple items to cold. Guard by cycling the queue.
                         Volatile.Write(ref this.isWarm, true);
-                        int coldCount = this.Move(item, ItemDestination.Cold, ItemRemovedReason.Evicted);
-                        CycleCold(coldCount);
+                        count = LastWarmToCold();
+                        ConstrainCold(count, ItemRemovedReason.Evicted);
                     }
                 }
                 else