Reworked WeakReferenceKey.Equals()

Author: tippmar-nr

src/Agent/NewRelic/Agent/Extensions/NewRelic.Agent.Extensions/Caching/WeakReferenceKey.cs

@@ -24,6 +24,13 @@ public override bool Equals(object obj)
         {
             if (obj is WeakReferenceKey<T> otherKey)
             {
+                if (WeakReference.TryGetTarget(out var thisTarget) &&
+                    otherKey.WeakReference.TryGetTarget(out var otherTarget))
+                {
+                    return ReferenceEquals(thisTarget, otherTarget);
+                }
+
+                // if one of the targets has been garbage collected, we can still compare the hashcodes
                 return otherKey.GetHashCode() == _hashCode;
             }
 
@@ -32,7 +39,7 @@ public override bool Equals(object obj)
 
         public override int GetHashCode()
         {
-            return _hashCode;
+            return WeakReference.TryGetTarget(out var target) ? target.GetHashCode() : _hashCode;
         }
 
         /// <summary>

tests/Agent/UnitTests/NewRelic.Agent.Extensions.Tests/Cache/WeakReferenceKeyTests.cs

@@ -150,6 +150,26 @@ public async Task Equals_ShouldReturnFalseIfTargetIsGarbageCollected()
             Assert.That(weakRefKey1.Equals(weakRefKey2), Is.False);
         }
 
+        [Test]
+        public async Task GetHashCode_ShouldReturnOriginalHashcodeIfTargetIsGarbageCollected()
+        {
+            // Arrange
+            var weakRefKey = GetWeakReferenceKey();
+            var originalHashCode = weakRefKey.GetHashCode();
+
+            // Act
+            Assert.That(weakRefKey.Value, Is.Not.Null);
+
+            // force garbage collection
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+            await Task.Delay(500);
+            GC.Collect(); // Force another collection
+
+            // Assert
+            Assert.That(weakRefKey.Value, Is.Null); // ensure GC really happened
+            Assert.That(weakRefKey.GetHashCode(), Is.EqualTo(originalHashCode));
+        }
         private class Foo
         {
             public string Bar { get; set; }