Merge pull request #1571 from microsoft/agents/diagnose-non-deterministic-failure

AsyncCrossProcessMutex: Fix foreground thread leak causing non-deterministic test host exit failure

Author: AArnott

src/Microsoft.VisualStudio.Threading/AsyncCrossProcessMutex.cs

@@ -56,6 +56,7 @@ public AsyncCrossProcessMutex(string name)
         Requires.NotNullOrEmpty(name);
         this.namedMutexOwner = new Thread(this.MutexOwnerThread, 256 * 1024)
         {
+            IsBackground = true,
             Name = $"{nameof(AsyncCrossProcessMutex)}-{name}",
         };
         this.mutex = new Mutex(false, name);

test/Microsoft.VisualStudio.Threading.Tests/AsyncCrossProcessMutexTests.cs

@@ -72,7 +72,7 @@ public async Task TryEnterAsync_Reentrancy()
     public async Task EnterAsync_Contested()
     {
         // We don't allow attempted reentrancy, so create a new mutex object to use for the contested locks.
-        AsyncCrossProcessMutex mutex2 = new(this.mutex.Name);
+        using AsyncCrossProcessMutex mutex2 = new(this.mutex.Name);
 
         // Acquire and hold the mutex so that we can test timeout behavior.
         using (AsyncCrossProcessMutex.LockReleaser releaser = await this.mutex.EnterAsync())
@@ -95,7 +95,7 @@ public async Task EnterAsync_Contested()
     public async Task TryEnterAsync_Contested()
     {
         // We don't allow attempted reentrancy, so create a new mutex object to use for the contested locks.
-        AsyncCrossProcessMutex mutex2 = new(this.mutex.Name);
+        using AsyncCrossProcessMutex mutex2 = new(this.mutex.Name);
 
         // Acquire and hold the mutex so that we can test timeout behavior.
         using (AsyncCrossProcessMutex.LockReleaser? releaser = await this.mutex.TryEnterAsync(Timeout.InfiniteTimeSpan))