From f958f2bf5f6be374719cb1fbdf17131551857dd4 Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Thu, 15 Apr 2021 09:57:04 -0400
Subject: [PATCH] Fix closure in
 HttpConnectionPoolManager.StartMonitoringNetworkChanges (#50487)

---
 .../HttpConnectionPoolManager.cs              | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
index b8fafcca13614..cf276ab93bb01 100644
--- a/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
+++ b/src/libraries/System.Net.Http/src/System/Net/Http/SocketsHttpHandler/HttpConnectionPoolManager.cs
@@ -163,17 +163,20 @@ public void StartMonitoringNetworkChanges()
 
             // Monitor network changes to invalidate Alt-Svc headers.
             // A weak reference is used to avoid NetworkChange.NetworkAddressChanged keeping a non-disposed connection pool alive.
-            var poolsRef = new WeakReference<ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>>(_pools);
-            NetworkAddressChangedEventHandler networkChangedDelegate = delegate
-            {
-                if (poolsRef.TryGetTarget(out ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>? pools))
+            NetworkAddressChangedEventHandler networkChangedDelegate;
+            { // scope to avoid closure if _networkChangeCleanup != null
+                var poolsRef = new WeakReference<ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>>(_pools);
+                networkChangedDelegate = delegate
                 {
-                    foreach (HttpConnectionPool pool in pools.Values)
+                    if (poolsRef.TryGetTarget(out ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>? pools))
                     {
-                        pool.OnNetworkChanged();
+                        foreach (HttpConnectionPool pool in pools.Values)
+                        {
+                            pool.OnNetworkChanged();
+                        }
                     }
-                }
-            };
+                };
+            }
 
             var cleanup = new NetworkChangeCleanup(networkChangedDelegate);