From fd818656eadcc515467a9348bc6c2ea30fb50388 Mon Sep 17 00:00:00 2001
From: Eduardo Velarde <evelardepola@microsoft.com>
Date: Mon, 12 Jan 2026 16:56:13 -0800
Subject: [PATCH 1/2] Fix Thread pool priority alternation

---
 .../src/System/Threading/ThreadPoolWorkQueue.cs                 | 2 +-
 1 file changed, 1 insertion(+), 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 0480f93dfa35b1..db65a53724f475 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
@@ -849,9 +849,9 @@ public long GlobalCount
             // take over the thread, sustaining starvation. For example, when worker threads are continually starved,
             // high-priority work items may always be queued and normal-priority work items may not get a chance to run.
             bool dispatchNormalPriorityWorkFirst = workQueue._dispatchNormalPriorityWorkFirst;
+            workQueue._dispatchNormalPriorityWorkFirst = !dispatchNormalPriorityWorkFirst;
             if (dispatchNormalPriorityWorkFirst && !tl.workStealingQueue.CanSteal)
             {
-                workQueue._dispatchNormalPriorityWorkFirst = !dispatchNormalPriorityWorkFirst;
                 WorkQueue queue =
                     s_assignableWorkItemQueueCount > 0 ? tl.assignedGlobalWorkItemQueue : workQueue.workItems;
                 if (!queue.TryDequeue(out workItem) && s_assignableWorkItemQueueCount > 0)

From 382cd7891bfdb26c5861eeeceb990a15f184daf9 Mon Sep 17 00:00:00 2001
From: Eduardo Velarde <evelardepola@microsoft.com>
Date: Fri, 23 Jan 2026 00:22:42 -0800
Subject: [PATCH 2/2] Remove dequeue with priority alternation

---
 .../System/Threading/ThreadPoolWorkQueue.cs   | 30 ++-----------------
 1 file changed, 2 insertions(+), 28 deletions(-)

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 db65a53724f475..d6c50b305d1e06 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolWorkQueue.cs
@@ -421,7 +421,6 @@ public int Count
                 (Environment.ProcessorCount + (ProcessorsPerAssignableWorkItemQueue - 1)) / ProcessorsPerAssignableWorkItemQueue;
 
         private bool _loggingEnabled;
-        private bool _dispatchNormalPriorityWorkFirst;
 
         // SOS's ThreadPool command depends on the following names
         internal readonly WorkQueue workItems = new WorkQueue();
@@ -840,32 +839,6 @@ public long GlobalCount
         // Dispatch (if YieldFromDispatchLoop is true), or performing periodic activities
         public const uint DispatchQuantumMs = 30;
 
-        private static object? DequeueWithPriorityAlternation(ThreadPoolWorkQueue workQueue, ThreadPoolWorkQueueThreadLocals tl, out bool missedSteal)
-        {
-            object? workItem = null;
-
-            // Alternate between checking for high-prioriy and normal-priority work first, that way both sets of work
-            // items get a chance to run in situations where worker threads are starved and work items that run also
-            // take over the thread, sustaining starvation. For example, when worker threads are continually starved,
-            // high-priority work items may always be queued and normal-priority work items may not get a chance to run.
-            bool dispatchNormalPriorityWorkFirst = workQueue._dispatchNormalPriorityWorkFirst;
-            workQueue._dispatchNormalPriorityWorkFirst = !dispatchNormalPriorityWorkFirst;
-            if (dispatchNormalPriorityWorkFirst && !tl.workStealingQueue.CanSteal)
-            {
-                WorkQueue queue =
-                    s_assignableWorkItemQueueCount > 0 ? tl.assignedGlobalWorkItemQueue : workQueue.workItems;
-                if (!queue.TryDequeue(out workItem) && s_assignableWorkItemQueueCount > 0)
-                {
-                    workQueue.workItems.TryDequeue(out workItem);
-                }
-            }
-
-            missedSteal = false;
-            workItem ??= workQueue.Dequeue(tl, ref missedSteal);
-
-            return workItem;
-        }
-
         /// <summary>
         /// Dispatches work items to this thread.
         /// </summary>
@@ -877,7 +850,8 @@ internal static bool Dispatch()
         {
             ThreadPoolWorkQueue workQueue = ThreadPool.s_workQueue;
             ThreadPoolWorkQueueThreadLocals tl = workQueue.GetOrCreateThreadLocals();
-            object? workItem = DequeueWithPriorityAlternation(workQueue, tl, out bool missedSteal);
+            bool missedSteal = false;
+            object? workItem = workQueue.Dequeue(tl, ref missedSteal);
             if (workItem == null)
             {
                 // Missing a steal means there may be an item that we were unable to get.