From 7c52a7bf5fe10f70b547b37f757a9ad022d29d1f Mon Sep 17 00:00:00 2001
From: marcos henrich <marcoshenrich@gmail.com>
Date: Thu, 29 May 2014 17:53:32 +0100
Subject: [PATCH] Overwrites dequeued ref/value with default. Fixes 18421.
 ConcurrentQueue was keeping the last dequeued ref/value.

---
 .../corlib/System.Collections.Concurrent/ConcurrentQueue.cs  | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mcs/class/corlib/System.Collections.Concurrent/ConcurrentQueue.cs b/mcs/class/corlib/System.Collections.Concurrent/ConcurrentQueue.cs
index d19cc4cec7d..aff2492e021 100644
--- a/mcs/class/corlib/System.Collections.Concurrent/ConcurrentQueue.cs
+++ b/mcs/class/corlib/System.Collections.Concurrent/ConcurrentQueue.cs
@@ -97,12 +97,13 @@ namespace System.Collections.Concurrent
 		public bool TryDequeue (out T result)
 		{
 			result = default (T);
+			Node oldNext = null;
 			bool advanced = false;
 
 			while (!advanced) {
 				Node oldHead = head;
 				Node oldTail = tail;
-				Node oldNext = oldHead.Next;
+				oldNext = oldHead.Next;
 				
 				if (oldHead == head) {
 					// Empty case ?
@@ -122,6 +123,8 @@ namespace System.Collections.Concurrent
 				}
 			}
 
+			oldNext.Value = default (T);
+
 			Interlocked.Decrement (ref count);
 
 			return true;
-- 
2.25.1