From 10a995276e09559ea4347a4e0c88f4402400132b Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Fri, 3 Oct 2025 10:57:36 -0700
Subject: [PATCH] Revert "Use a ReaderWriterLockSlim in RcwCache (#117792)"

This reverts commit a0748134c931391cf310f8eb4b78d4874f378463.
---
 .../Runtime/InteropServices/ComWrappers.cs    | 23 ++++---------------
 1 file changed, 4 insertions(+), 19 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ComWrappers.cs b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ComWrappers.cs
index 2945a99d9b8c44..840f05dc00f856 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ComWrappers.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Runtime/InteropServices/ComWrappers.cs
@@ -1289,7 +1289,7 @@ private static void AddWrapperToReferenceTrackerHandleCache(NativeObjectWrapper
 
         private sealed class RcwCache
         {
-            private readonly ReaderWriterLockSlim _lock = new ReaderWriterLockSlim();
+            private readonly Lock _lock = new Lock(useTrivialWaits: true);
             private readonly Dictionary<IntPtr, GCHandle> _cache = [];
 
             /// <summary>
@@ -1301,8 +1301,7 @@ private sealed class RcwCache
             /// <returns>The proxy object currently in the cache for <paramref name="comPointer"/> or the proxy object owned by <paramref name="wrapper"/> if no entry exists and the corresponding native wrapper.</returns>
             public (NativeObjectWrapper actualWrapper, object actualProxy) GetOrAddProxyForComInstance(IntPtr comPointer, NativeObjectWrapper wrapper, object comProxy)
             {
-                _lock.EnterWriteLock();
-                try
+                lock (_lock)
                 {
                     Debug.Assert(wrapper.ProxyHandle.Target == comProxy);
                     ref GCHandle rcwEntry = ref CollectionsMarshal.GetValueRefOrAddDefault(_cache, comPointer, out bool exists);
@@ -1337,16 +1336,11 @@ private sealed class RcwCache
                     // Return our target object.
                     return (wrapper, comProxy);
                 }
-                finally
-                {
-                    _lock.ExitWriteLock();
-                }
             }
 
             public object? FindProxyForComInstance(IntPtr comPointer)
             {
-                _lock.EnterReadLock();
-                try
+                lock (_lock)
                 {
                     if (_cache.TryGetValue(comPointer, out GCHandle existingHandle))
                     {
@@ -1363,16 +1357,11 @@ private sealed class RcwCache
 
                     return null;
                 }
-                finally
-                {
-                    _lock.ExitReadLock();
-                }
             }
 
             public void Remove(IntPtr comPointer, NativeObjectWrapper wrapper)
             {
-                _lock.EnterWriteLock();
-                try
+                lock (_lock)
                 {
                     // TryGetOrCreateObjectForComInstanceInternal may have put a new entry into the cache
                     // in the time between the GC cleared the contents of the GC handle but before the
@@ -1387,10 +1376,6 @@ public void Remove(IntPtr comPointer, NativeObjectWrapper wrapper)
                         cachedRef.Free();
                     }
                 }
-                finally
-                {
-                    _lock.ExitWriteLock();
-                }
             }
         }