From b1d42b5b72fdbc70b8541756471357d6ba79c32a Mon Sep 17 00:00:00 2001
From: Aaron Robinson <arobins@microsoft.com>
Date: Mon, 12 Apr 2021 17:02:40 -0700
Subject: [PATCH] Fix race in ComWrappers test

Since the finalizer thread runs async with the test, we need to
atomically decrement the static instance counter.
---
 src/tests/Interop/COM/ComWrappers/Common.cs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/tests/Interop/COM/ComWrappers/Common.cs b/src/tests/Interop/COM/ComWrappers/Common.cs
index 5d1994131e7a76..4aa98b76e9031c 100644
--- a/src/tests/Interop/COM/ComWrappers/Common.cs
+++ b/src/tests/Interop/COM/ComWrappers/Common.cs
@@ -21,9 +21,10 @@ class Test : ITest, ICustomQueryInterface
     {
         public static int InstanceCount = 0;
 
+        private int id;
         private int value = -1;
-        public Test() { InstanceCount++; }
-        ~Test() { InstanceCount--; }
+        public Test() { id = Interlocked.Increment(ref InstanceCount); }
+        ~Test() { Interlocked.Decrement(ref InstanceCount); id = -1; }
 
         public void SetValue(int i) => this.value = i;
         public int GetValue() => this.value;