fix during warmup

Author: Alex Peck

BitFaster.Caching.UnitTests/Lru/ConcurrentLruTests.cs

@@ -678,6 +678,44 @@ public void WhenItemIsRemovedRemovedEventIsFired()
             removedItems[0].Reason.Should().Be(ItemRemovedReason.Removed);
         }
 
+        [Fact]
+        public void WhenItemRemovedFromHotDuringWarmupItIsEagerlyCycledOut()
+        {
+            lru.GetOrAdd(1, valueFactory.Create);
+
+            lru.TryRemove(1);
+
+            lru.GetOrAdd(1, valueFactory.Create);
+            lru.GetOrAdd(2, valueFactory.Create);
+            lru.GetOrAdd(3, valueFactory.Create);
+
+            lru.WarmCount.Should().Be(0);
+            lru.ColdCount.Should().Be(0);
+        }
+
+        [Fact]
+        public void WhenItemRemovedFromHotAfterWarmupItIsEagerlyCycledOut()
+        {
+            for (int i = 0; i < lru.Capacity; i++)
+            {
+                lru.GetOrAdd(i, valueFactory.Create);
+            }
+
+            lru.Metrics.Value.Evicted.Should().Be(0);
+
+            lru.GetOrAdd(-1, valueFactory.Create);
+
+            lru.TryRemove(-1);
+
+            // fully cycle hot, which is 3 items
+            lru.GetOrAdd(-2, valueFactory.Create);
+            lru.GetOrAdd(-3, valueFactory.Create);
+            lru.GetOrAdd(-4, valueFactory.Create);
+
+            // without eager eviction as -1 is purged from hot, a 4th item will pushed out since hot queue is full
+            lru.Metrics.Value.Evicted.Should().Be(3);
+        }
+
         [Fact]
         public void WhenKeyDoesNotExistTryRemoveReturnsFalse()
         {

BitFaster.Caching/Lru/ConcurrentLruCore.cs

@@ -624,6 +624,12 @@ private void CycleDuringWarmup(int hotCount)
 
                 if (this.hotQueue.TryDequeue(out var item))
                 {
+                    // special case: removed during warmup
+                    if (item.WasRemoved)
+                    {
+                        return;
+                    }
+
                     int count = this.Move(item, ItemDestination.Warm, ItemRemovedReason.Evicted);
 
                     // if warm is now full, overflow to cold and mark as warm