From d5d159eb5fa682c7a0bf53bf8a8caa7d7a7651b4 Mon Sep 17 00:00:00 2001
From: BrennanConroy <brecon@microsoft.com>
Date: Wed, 3 Jan 2018 12:29:25 -0800
Subject: [PATCH] Lock around heartbeat handler (#1264)

---
 .../DefaultConnectionContext.cs                      | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Sockets/DefaultConnectionContext.cs b/src/Microsoft.AspNetCore.Sockets/DefaultConnectionContext.cs
index b27b9543cd..6faa0b0b26 100644
--- a/src/Microsoft.AspNetCore.Sockets/DefaultConnectionContext.cs
+++ b/src/Microsoft.AspNetCore.Sockets/DefaultConnectionContext.cs
@@ -75,14 +75,20 @@ namespace Microsoft.AspNetCore.Sockets
 
         public void OnHeartbeat(Action<object> action, object state)
         {
-            _heartbeatHandlers.Add((action, state));
+            lock (_heartbeatHandlers)
+            {
+                _heartbeatHandlers.Add((action, state));
+            }
         }
 
         public void TickHeartbeat()
         {
-            foreach (var (handler, state) in _heartbeatHandlers)
+            lock (_heartbeatHandlers)
             {
-                handler(state);
+                foreach (var (handler, state) in _heartbeatHandlers)
+                {
+                    handler(state);
+                }
             }
         }