lifetime reference counting (#52)

Author: bitfaster

BitFaster.Caching.UnitTests/SingletonCacheTests.cs

@@ -32,6 +32,31 @@ public void AcquireWithSameKeyReturnsSameLifetime()
             lifetime2.Dispose();
         }
 
+        [Fact]
+        public void AcquireWithSameKeyMaintainsReferenceCount()
+        {
+            var cache = new SingletonCache<string, object>();
+
+            using (var lifetime1 = cache.Acquire("Foo"))
+            {
+                using (var lifetime2 = cache.Acquire("Foo"))
+                {
+                    lifetime1.ReferenceCount.Should().Be(1);
+                    lifetime2.ReferenceCount.Should().Be(2);
+                }
+
+                using (var lifetime3 = cache.Acquire("Foo"))
+                {
+                    lifetime3.ReferenceCount.Should().Be(2);
+                }
+            }
+
+            using (var lifetime4 = cache.Acquire("Foo"))
+            {
+                lifetime4.ReferenceCount.Should().Be(1);
+            }
+        }
+
         [Fact]
         public void AcquireReleaseAcquireReturnsDifferentValue()
         {

BitFaster.Caching/Lifetime.cs

@@ -12,23 +12,29 @@ namespace BitFaster.Caching
     public class Lifetime<T> : IDisposable
     {
         private readonly Action onDisposeAction;
+        private readonly ReferenceCount<T> refCount;
         private bool isDisposed;
 
         /// <summary>
         /// Initializes a new instance of the Lifetime class.
         /// </summary>
         /// <param name="value">The value to keep alive.</param>
         /// <param name="onDisposeAction">The action to perform when the lifetime is terminated.</param>
-        public Lifetime(T value, Action onDisposeAction)
+        public Lifetime(ReferenceCount<T> value, Action onDisposeAction)
         {
-            this.Value = value;
+            this.refCount = value;
             this.onDisposeAction = onDisposeAction;
         }
 
         /// <summary>
         /// Gets the value.
         /// </summary>
-        public T Value { get; }
+        public T Value => this.refCount.Value;
+
+        /// <summary>
+        /// Gets the count of Lifetime instances referencing the same value.
+        /// </summary>
+        public int ReferenceCount => this.refCount.Count;
 
         /// <summary>
         /// Terminates the lifetime and performs any cleanup required to release the value.

BitFaster.Caching/Scoped.cs

@@ -48,7 +48,7 @@ public Lifetime<T> CreateLifetime()
                 if (oldRefCount == Interlocked.CompareExchange(ref this.refCount, newRefCount, oldRefCount))
                 {
                     // When Lease is disposed, it calls DecrementReferenceCount
-                    return new Lifetime<T>(oldRefCount.Value, this.DecrementReferenceCount);
+                    return new Lifetime<T>(oldRefCount, this.DecrementReferenceCount);
                 }
             }
         }

BitFaster.Caching/SingletonCache.cs

@@ -52,7 +52,7 @@ public Lifetime<TValue> Acquire(TKey key, Func<TKey, TValue> valueFactory)
                     (k) => new ReferenceCount<TValue>(valueFactory(k)),
                     (_, existingRefCount) => existingRefCount.IncrementCopy());
 
-            return new Lifetime<TValue>(refCount.Value, () => this.Release(key));
+            return new Lifetime<TValue>(refCount, () => this.Release(key));
         }
 
         private void Release(TKey key)