From 3e7c20f906ddf21938bd5efa7ebe6e1525fdef16 Mon Sep 17 00:00:00 2001
From: Eduardo Velarde <32459232+eduardo-vp@users.noreply.github.com>
Date: Tue, 27 Aug 2024 18:53:10 -0700
Subject: [PATCH] Stop counting work items from ThreadPoolTypedWorkItemQueue
 for ThreadPool.CompletedWorkItemCount (#106854)

* Stop counting work items from ThreadPoolTypedWorkItemQueue as completed work items

* Fix CompletedWorkItemCount

* Update src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs

Co-authored-by: Koundinya Veluri <kouvel@users.noreply.github.com>

* Run CompletedWorkItemCountTest on Windows only

---------

Co-authored-by: Eduardo Manuel Velarde Polar <evelardepola@microsoft.com>
Co-authored-by: Koundinya Veluri <kouvel@users.noreply.github.com>
---
 .../System/Threading/ThreadPoolWorkQueue.cs   |  6 ++++-
 .../tests/ThreadPoolTests.cs                  | 27 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
index bc0fe4556bb31..89dac7492578f 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
@@ -1393,7 +1393,11 @@ void IThreadPoolWorkItem.Execute()
                 currentThread.ResetThreadPoolThread();
             }
 
-            ThreadInt64PersistentCounter.Add(tl.threadLocalCompletionCountObject!, completedCount);
+            // Discount a work item here to avoid counting most of the queue processing work items
+            if (completedCount > 1)
+            {
+                ThreadInt64PersistentCounter.Add(tl.threadLocalCompletionCountObject!, completedCount - 1);
+            }
         }
     }
 
diff --git a/src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs b/src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs
index a182c7c583630..a26b000055a7f 100644
--- a/src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs
+++ b/src/libraries/System.Threading.ThreadPool/tests/ThreadPoolTests.cs
@@ -1440,6 +1440,33 @@ static async Task RunAsyncIOTest()
             }, ioCompletionPortCount.ToString()).Dispose();
         }
 
+
+        [ConditionalFact(nameof(IsThreadingAndRemoteExecutorSupported))]
+        [PlatformSpecific(TestPlatforms.Windows)]
+        public static unsafe void ThreadPoolCompletedWorkItemCountTest()
+        {
+            // Run in a separate process to test in a clean thread pool environment such that we don't count external work items
+            RemoteExecutor.Invoke(() =>
+            {
+                using var manualResetEvent = new ManualResetEventSlim(false);
+
+                var overlapped = new Overlapped();
+                NativeOverlapped* nativeOverlapped = overlapped.Pack((errorCode, numBytes, innerNativeOverlapped) =>
+                {
+                    Overlapped.Free(innerNativeOverlapped);
+                    manualResetEvent.Set();
+                }, null);
+
+                ThreadPool.UnsafeQueueNativeOverlapped(nativeOverlapped);
+                manualResetEvent.Wait();
+
+                // Allow work item(s) to be marked as completed during this time, should be only one
+                ThreadTestHelpers.WaitForCondition(() => ThreadPool.CompletedWorkItemCount == 1);
+                Thread.Sleep(50);
+                Assert.Equal(1, ThreadPool.CompletedWorkItemCount);
+            }).Dispose();
+        }
+
         public static bool IsThreadingAndRemoteExecutorSupported =>
             PlatformDetection.IsThreadingSupported && RemoteExecutor.IsSupported;