From 2875435ce8052f2b57adcf3c918657a66d5b214e Mon Sep 17 00:00:00 2001
From: D3-LucaPiombino <luca.piombino@deltatre.com>
Date: Thu, 23 Oct 2014 16:02:44 +0200
Subject: [PATCH] [FIXED]: Issue #401 - Use reference equality to compare
 object instances when checking for circular references in a object graph.

---
 .../PreserveReferencesHandlingTests.cs        | 34 +++++++++++++++++++
 .../JsonSerializerInternalWriter.cs           |  2 +-
 2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/Src/Newtonsoft.Json.Tests/Serialization/PreserveReferencesHandlingTests.cs b/Src/Newtonsoft.Json.Tests/Serialization/PreserveReferencesHandlingTests.cs
index 4bbe6214f..0121a7463 100644
--- a/Src/Newtonsoft.Json.Tests/Serialization/PreserveReferencesHandlingTests.cs
+++ b/Src/Newtonsoft.Json.Tests/Serialization/PreserveReferencesHandlingTests.cs
@@ -1065,6 +1065,17 @@ public void DuplicateId()
                 MetadataPropertyHandling = MetadataPropertyHandling.Default
             }), "Error reading object reference '1'. Path 'Data.Prop2.MyProperty', line 9, position 20.");
         }
+
+        [Test]
+        public void ShouldCheckForCircularReferencesUsingReferenceEquality()
+        {
+            var source = new ValueContainer
+            {
+                Value = new object()
+            };
+
+            string json = JsonConvert.SerializeObject(source, Formatting.Indented);
+        }
     }
 
     public class PropertyItemIsReferenceBody
@@ -1108,4 +1119,27 @@ public class ReferenceObject
         public string String { get; set; }
         public int Integer { get; set; }
     }
+
+    public class ValueContainer
+    {
+        public object Value;
+
+        public override bool Equals(object obj)
+        {
+            if (obj == null)
+                return false;
+
+            var otherContainer = obj as ValueContainer;
+
+            if (otherContainer != null)
+                return EqualityComparer<object>.Default.Equals(Value, otherContainer.Value);
+
+            return EqualityComparer<object>.Default.Equals(Value, obj);
+        }
+
+        public override int GetHashCode()
+        {
+            return EqualityComparer<object>.Default.GetHashCode(Value);
+        }
+    }
 }
\ No newline at end of file
diff --git a/Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs b/Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs
index 84c5358f6..7c53a59b3 100644
--- a/Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs
+++ b/Src/Newtonsoft.Json/Serialization/JsonSerializerInternalWriter.cs
@@ -265,7 +265,7 @@ private bool CheckForCircularReference(JsonWriter writer, object value, JsonProp
             if (referenceLoopHandling == null && containerContract != null)
                 referenceLoopHandling = containerContract.ItemReferenceLoopHandling;
 
-            if (_serializeStack.IndexOf(value) != -1)
+            if (_serializeStack.IndexOf(itemOnStack => object.ReferenceEquals(itemOnStack,value)) != -1)
             {
                 string message = "Self referencing loop detected";
                 if (property != null)