From b99de67b5d6049b156d96f7d8f86de647b2e49c6 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Wed, 27 Dec 2017 00:47:11 +0000
Subject: [PATCH 1/2] Don't capture AsyncLocals into HttpConnectionPools timer

---
 .../src/System/Net/Http/Managed/HttpConnectionPools.cs       | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs b/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
index 2650b7bab385..441e957672dc 100644
--- a/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
+++ b/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
@@ -39,7 +39,12 @@ public HttpConnectionPools(int maxConnectionsPerServer)
             _maxConnectionsPerServer = maxConnectionsPerServer;
             _pools = new ConcurrentDictionary<HttpConnectionKey, HttpConnectionPool>();
             // Start out with the timer not running, since we have no pools.
+
+            // Don't capture the current ExecutionContext and its AsyncLocals onto the timer causing them to live forever
+            ExecutionContext.SuppressFlow();
             _cleaningTimer = new Timer(s => ((HttpConnectionPools)s).RemoveStalePools(), this, Timeout.Infinite, Timeout.Infinite);
+            // Restore the current ExecutionContext
+            ExecutionContext.RestoreFlow();
         }
 
         /// <summary>Gets a pool for the specified endpoint, adding one if none existed.</summary>

From 561c1a695ce90eb6ede6d0a4af179124b53db314 Mon Sep 17 00:00:00 2001
From: Ben Adams <thundercat@illyriad.co.uk>
Date: Wed, 27 Dec 2017 21:02:36 +0000
Subject: [PATCH 2/2] Harden EC flow suppression

---
 .../Net/Http/Managed/HttpConnectionPools.cs   | 21 +++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs b/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
index 441e957672dc..d1d043b5432b 100644
--- a/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
+++ b/src/System.Net.Http/src/System/Net/Http/Managed/HttpConnectionPools.cs
@@ -41,10 +41,23 @@ public HttpConnectionPools(int maxConnectionsPerServer)
             // Start out with the timer not running, since we have no pools.
 
             // Don't capture the current ExecutionContext and its AsyncLocals onto the timer causing them to live forever
-            ExecutionContext.SuppressFlow();
-            _cleaningTimer = new Timer(s => ((HttpConnectionPools)s).RemoveStalePools(), this, Timeout.Infinite, Timeout.Infinite);
-            // Restore the current ExecutionContext
-            ExecutionContext.RestoreFlow();
+            bool restoreFlow = false;
+            try
+            {
+                if (!ExecutionContext.IsFlowSuppressed())
+                {
+                    ExecutionContext.SuppressFlow();
+                    restoreFlow = true;
+                }
+
+                _cleaningTimer = new Timer(s => ((HttpConnectionPools)s).RemoveStalePools(), this, Timeout.Infinite, Timeout.Infinite);
+            }
+            finally
+            {
+                // Restore the current ExecutionContext
+                if (restoreFlow)
+                    ExecutionContext.RestoreFlow();
+            }
         }
 
         /// <summary>Gets a pool for the specified endpoint, adding one if none existed.</summary>