From 43a164f42fe0bc8776687d906ad07f0a707a87fb Mon Sep 17 00:00:00 2001
From: Steve Molloy <smolloy@microsoft.com>
Date: Thu, 11 Jul 2024 11:16:28 -0700
Subject: [PATCH 1/2] Don't dispose timers if we're in our UnhandledException
 handler. (#103937)

---
 .../src/System/Runtime/Caching/MemoryCache.cs     |  6 ++++++
 .../Runtime/Caching/MemoryCacheStatistics.cs      | 15 +++++++++++++--
 .../src/System/Runtime/Caching/SRef.cs            |  5 +++++
 3 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCache.cs b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCache.cs
index e740eed69ed514..e2c99f5a92e050 100644
--- a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCache.cs
+++ b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCache.cs
@@ -40,6 +40,7 @@ public class MemoryCache : ObjectCache, IEnumerable, IDisposable
         private bool _throwOnDisposed;
         private EventHandler _onAppDomainUnload;
         private UnhandledExceptionEventHandler _onUnhandledException;
+        private int _inUnhandledExceptionHandler;
 #if NETCOREAPP
         [UnsupportedOSPlatformGuard("browser")]
         private static bool _countersSupported => !OperatingSystem.IsBrowser();
@@ -238,14 +239,19 @@ private void OnAppDomainUnload(object unusedObject, EventArgs unusedEventArgs)
             Dispose();
         }
 
+        internal bool InUnhandledExceptionHandler => _inUnhandledExceptionHandler > 0;
         private void OnUnhandledException(object sender, UnhandledExceptionEventArgs eventArgs)
         {
+            Interlocked.Increment(ref _inUnhandledExceptionHandler);
+
             // if the CLR is terminating, dispose the cache.
             // This will dispose the perf counters
             if (eventArgs.IsTerminating)
             {
                 Dispose();
             }
+
+            Interlocked.Decrement(ref _inUnhandledExceptionHandler);
         }
 
         private static void ValidatePolicy(CacheItemPolicy policy)
diff --git a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCacheStatistics.cs b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCacheStatistics.cs
index 96cfc3bda655bd..0599e8febc593c 100644
--- a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCacheStatistics.cs
+++ b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/MemoryCacheStatistics.cs
@@ -340,8 +340,19 @@ public void Dispose()
                     GCHandleRef<Timer> timerHandleRef = _timerHandleRef;
                     if (timerHandleRef != null && Interlocked.CompareExchange(ref _timerHandleRef, null, timerHandleRef) == timerHandleRef)
                     {
-                        timerHandleRef.Dispose();
-                        Dbg.Trace("MemoryCacheStats", "Stopped CacheMemoryTimers");
+                        // If inside an unhandled exception handler, Timers may be succeptible to deadlocks. Use a safer approach.
+                        if (_memoryCache.InUnhandledExceptionHandler)
+                        {
+                            // This does not stop/dispose the timer. But the callback on the timer is protected by _disposed, which we have already
+                            // set above.
+                            timerHandleRef.FreeHandle();
+                            Dbg.Trace("MemoryCacheStats", "Freed CacheMemoryTimers");
+                        }
+                        else
+                        {
+                            timerHandleRef.Dispose();
+                            Dbg.Trace("MemoryCacheStats", "Stopped CacheMemoryTimers");
+                        }
                     }
                 }
                 while (_inCacheManagerThread != 0)
diff --git a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/SRef.cs b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/SRef.cs
index 9a09ba1d9781ae..412f66971a7fea 100644
--- a/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/SRef.cs
+++ b/src/libraries/System.Runtime.Caching/src/System/Runtime/Caching/SRef.cs
@@ -59,6 +59,11 @@ public T Target
         public void Dispose()
         {
             Target.Dispose();
+            FreeHandle();
+        }
+
+        internal void FreeHandle()
+        {
             // Safe to call Dispose more than once but not thread-safe
             if (_handle.IsAllocated)
             {

From e9d7d615666906ab24b8d65a68ec194ade2a95d0 Mon Sep 17 00:00:00 2001
From: Steve Molloy <smolloy@microsoft.com>
Date: Tue, 16 Jul 2024 11:23:35 -0700
Subject: [PATCH 2/2] Update Sys.RT.Caching csproj for servicing build.

---
 .../System.Runtime.Caching/src/System.Runtime.Caching.csproj    | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj b/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
index b3d85127f02129..241cbbffb21367 100644
--- a/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
+++ b/src/libraries/System.Runtime.Caching/src/System.Runtime.Caching.csproj
@@ -3,6 +3,8 @@
     <TargetFrameworks>$(NetCoreAppCurrent)-windows;$(NetCoreAppCurrent);$(NetCoreAppPrevious)-windows;$(NetCoreAppPrevious);$(NetCoreAppMinimum)-windows;$(NetCoreAppMinimum);netstandard2.0</TargetFrameworks>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <IsPackable>true</IsPackable>
+    <GeneratePackageOnBuild>true</GeneratePackageOnBuild>
+    <ServicingVersion>1</ServicingVersion>
     <AddNETFrameworkPlaceholderFileToPackage>true</AddNETFrameworkPlaceholderFileToPackage>
     <AddXamarinPlaceholderFilesToPackage>true</AddXamarinPlaceholderFilesToPackage>
     <AddNETFrameworkAssemblyReferenceToPackage>true</AddNETFrameworkAssemblyReferenceToPackage>