From 6c7dccf78f37350da2f3d37585c9186b6202fbdc Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 12 Mar 2026 18:05:09 +0000
Subject: [PATCH 01/22] Initial plan


From f9012f73697c550c41c22a99b796e065e032e6e4 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 12 Mar 2026 18:41:43 +0000
Subject: [PATCH 02/22] De-duplicate PreAllocatedOverlapped.Browser.cs and
 PreAllocatedOverlapped.Unix.cs, remove ILLink workaround

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/ILLink/ILLink.Descriptors.Shared.xml       |  9 ---------
 .../src/System.Private.CoreLib.Shared.projitems    | 11 +++++++----
 .../Threading/PreAllocatedOverlapped.Browser.cs    | 14 --------------
 3 files changed, 7 insertions(+), 27 deletions(-)
 delete mode 100644 src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Browser.cs

diff --git a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml
index f7e6fd1f2f0606..1730d7fe5b1291 100644
--- a/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml
+++ b/src/libraries/System.Private.CoreLib/src/ILLink/ILLink.Descriptors.Shared.xml
@@ -1,13 +1,4 @@
 <linker>
-  <assembly fullname="System.Private.CoreLib">
-    <type fullname="System.Threading.ThreadPoolBoundHandle">
-      <!-- Workaround to keep .interfaceimpl even though this type
-             is not instantiated on unix:
-             https://github.com/mono/linker/pull/649 -->
-      <method name=".ctor" />
-    </type>
-  </assembly>
-
   <assembly fullname="System.Private.CoreLib" feature="System.Runtime.InteropServices.EnableConsumingManagedCodeFromNativeHosting" featurevalue="true">
     <!-- Native hosting accesses managed methods from
     https://github.com/dotnet/runtime/blob/bbc898f3e5678135b242faeb6eefd8b24bf04f3c/src/native/corehost/hostpolicy/hostpolicy.cpp#L527-L538
diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index f040846c83487b..32fe98ab43e96e 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2853,20 +2853,23 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true' or '$(TargetsWasi)' == 'true'"  />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or ('$(TargetsBrowser)' == 'true' and '$(FeatureWasmManagedThreads)' == 'true')" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" Condition="('$(TargetsBrowser)' != 'true' and '$(TargetsWasi)' != 'true') or '$(FeatureWasmManagedThreads)' == 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
+  </ItemGroup>
   <ItemGroup Condition="('$(TargetsBrowser)' == 'true' or '$(TargetsWasi)' == 'true') and '$(FeatureWasmManagedThreads)' != 'true'">
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Browser.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Browser.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true' and '$(FeatureWasmManagedThreads)' != 'true'">
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Browser.cs
deleted file mode 100644
index caad4d140aa403..00000000000000
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Browser.cs
+++ /dev/null
@@ -1,14 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-namespace System.Threading
-{
-    public sealed class PreAllocatedOverlapped : System.IDisposable
-    {
-        [CLSCompliantAttribute(false)]
-        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) { }
-        [CLSCompliantAttribute(false)]
-        public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) => new PreAllocatedOverlapped(callback, state, pinData);
-        public void Dispose() { }
-    }
-}

From c4043c1be0231a6cf46f6c2ee8665db3dcfe8cd8 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 06:11:32 +0000
Subject: [PATCH 03/22] Include PreAllocatedOverlapped.Portable.cs
 unconditionally in FeaturePortableThreadPool block

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems               | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 38ef068a203be3..e47925afc39d24 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2872,7 +2872,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true' or '$(TargetsWasi)' == 'true'"  />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
@@ -2885,9 +2885,9 @@
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Browser.cs" />
   </ItemGroup>

From 2fd9e732b5e12d9f5c4ea30ddd6fa29f78c43b5a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 07:21:42 +0000
Subject: [PATCH 04/22] Simplify .Unix.cs conditions in
 FeaturePortableThreadPool block to TargetsWindows != true

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems             | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index e47925afc39d24..03767817ab5692 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2855,7 +2855,7 @@
   <ItemGroup Condition="'$(FeaturePortableThreadPool)' == 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\CompleteWaitThreadPoolWorkItem.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Portable.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true' or '$(TargetsWasi)' == 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.Blocking.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.GateThread.cs" />
@@ -2866,11 +2866,11 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.WaitThread.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.WorkerThread.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.WorkerTracking.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or ('$(TargetsBrowser)' == 'true' and '$(FeatureMultithreading)' != 'true') or '$(TargetsWasi)' == 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PortableThreadPool.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsUnix)' == 'true' or '$(TargetsBrowser)' == 'true' or '$(TargetsWasi)' == 'true'"  />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />

From 044c13b4221975429d2579914ebeaf44ce2270bb Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Wed, 18 Mar 2026 07:33:22 +0000
Subject: [PATCH 05/22] Add PreAllocatedOverlapped.Unix.cs into
 FeaturePortableThreadPool block; remove standalone TargetsWindows block

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems              | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 03767817ab5692..7586b13cb84c21 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2873,6 +2873,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
@@ -2883,11 +2884,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" />
-  </ItemGroup>
   <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Browser.cs" />
   </ItemGroup>

From 029f2d46fec4d94d1dc37bd8fe53bff434915fae Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 02:39:16 +0000
Subject: [PATCH 06/22] =?UTF-8?q?Sort=20PreAllocatedOverlapped=20entries?=
 =?UTF-8?q?=20alphabetically=20(Portable=20=E2=86=92=20Unix=20=E2=86=92=20?=
 =?UTF-8?q?Windows)?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../src/System.Private.CoreLib.Shared.projitems                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 7586b13cb84c21..5cf3d4c172a0a3 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2871,9 +2871,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />

From 8ddec44f5324cc15c932fff035855c276579e19a Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 03:02:55 +0000
Subject: [PATCH 07/22] Sort ThreadPoolBoundHandleOverlapped.cs before
 ThreadPoolCallbackWrapper.cs alphabetically

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 5cf3d4c172a0a3..6d601bf9812bed 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2880,8 +2880,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">

From 2671b4d8f91055aea0dcb7b7832bf3d951f64302 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 03:23:33 +0000
Subject: [PATCH 08/22] Add PreAllocatedOverlapped.NotSupported.cs; simplify
 FeatureMultithreading != true block

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../System.Private.CoreLib.Shared.projitems    |  4 +---
 .../PreAllocatedOverlapped.NotSupported.cs     | 18 ++++++++++++++++++
 2 files changed, 19 insertions(+), 3 deletions(-)
 create mode 100644 src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 6d601bf9812bed..a0fe4dcd48e15f 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2885,9 +2885,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Browser.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true' and '$(FeatureMultithreading)' != 'true'">
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
new file mode 100644
index 00000000000000..20d3b7aaed01f1
--- /dev/null
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
@@ -0,0 +1,18 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+namespace System.Threading
+{
+    public sealed class PreAllocatedOverlapped : System.IDisposable
+    {
+        [CLSCompliant(false)]
+        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
+            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
+
+        [CLSCompliant(false)]
+        public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
+            new PreAllocatedOverlapped(callback, state, pinData);
+
+        public void Dispose() { }
+    }
+}

From 6dfaec0eb15dfe162dcf53f1621916c0863256e1 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 03:31:39 +0000
Subject: [PATCH 09/22] =?UTF-8?q?Rename=20Browser.cs=20=E2=86=92=20NotSupp?=
 =?UTF-8?q?orted.cs;=20use=20NotSupported.cs=20for=20all=20non-Windows;=20?=
 =?UTF-8?q?delete=20Unix.cs=20files?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../System.Private.CoreLib.Shared.projitems   |  10 +-
 .../Threading/PreAllocatedOverlapped.Unix.cs  | 124 ---------
 ... => ThreadPoolBoundHandle.NotSupported.cs} |   0
 .../Threading/ThreadPoolBoundHandle.Unix.cs   | 255 ------------------
 4 files changed, 5 insertions(+), 384 deletions(-)
 delete mode 100644 src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Unix.cs
 rename src/libraries/System.Private.CoreLib/src/System/Threading/{ThreadPoolBoundHandle.Browser.cs => ThreadPoolBoundHandle.NotSupported.cs} (100%)
 delete mode 100644 src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Unix.cs

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index a0fe4dcd48e15f..450cfe01f6ce53 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2871,14 +2871,14 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" Condition="'$(TargetsWindows)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.NotSupported.cs" Condition="'$(TargetsWindows)' != 'true'" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
@@ -2886,7 +2886,7 @@
   </ItemGroup>
   <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Browser.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.NotSupported.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true' and '$(FeatureMultithreading)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Browser.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Unix.cs
deleted file mode 100644
index d638e6773f2cef..00000000000000
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.Unix.cs
+++ /dev/null
@@ -1,124 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Diagnostics;
-
-namespace System.Threading
-{
-    /// <summary>
-    /// Represents pre-allocated state for native overlapped I/O operations.
-    /// </summary>
-    /// <seealso cref="ThreadPoolBoundHandle.AllocateNativeOverlapped(PreAllocatedOverlapped)"/>
-    public sealed partial class PreAllocatedOverlapped : IDisposable, IDeferredDisposable
-    {
-        /// <summary>
-        ///     Initializes a new instance of the <see cref="PreAllocatedOverlapped"/> class, specifying
-        ///     a delegate that is invoked when each asynchronous I/O operation is complete, a user-provided
-        ///     object providing context, and managed objects that serve as buffers.
-        /// </summary>
-        /// <param name="callback">
-        ///     An <see cref="IOCompletionCallback"/> delegate that represents the callback method
-        ///     invoked when each asynchronous I/O operation completes.
-        /// </param>
-        /// <param name="state">
-        ///     A user-provided object that distinguishes <see cref="NativeOverlapped"/> instance produced from this
-        ///     object from other <see cref="NativeOverlapped"/> instances. Can be <see langword="null"/>.
-        /// </param>
-        /// <param name="pinData">
-        ///     An object or array of objects representing the input or output buffer for the operations. Each
-        ///     object represents a buffer, for example an array of bytes.  Can be <see langword="null"/>.
-        /// </param>
-        /// <remarks>
-        ///     The new <see cref="PreAllocatedOverlapped"/> instance can be passed to
-        ///     <see cref="ThreadPoolBoundHandle.AllocateNativeOverlapped(PreAllocatedOverlapped)"/>, to produce
-        ///     a <see cref="NativeOverlapped"/> instance that can be passed to the operating system in overlapped
-        ///     I/O operations.  A single <see cref="PreAllocatedOverlapped"/> instance can only be used for
-        ///     a single native I/O operation at a time.  However, the state stored in the <see cref="PreAllocatedOverlapped"/>
-        ///     instance can be reused for subsequent native operations.
-        ///     <note>
-        ///         The buffers specified in <paramref name="pinData"/> are pinned until <see cref="Dispose"/> is called.
-        ///     </note>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="callback"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed.
-        /// </exception>
-        [CLSCompliant(false)]
-        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) :
-            this(callback, state, pinData, flowExecutionContext: true)
-        {
-        }
-
-        private DeferredDisposableLifetime<PreAllocatedOverlapped> _lifetime;
-
-        /// <summary>
-        ///     Initializes a new instance of the <see cref="PreAllocatedOverlapped"/> class, specifying
-        ///     a delegate that is invoked when each asynchronous I/O operation is complete, a user-provided
-        ///     object providing context, and managed objects that serve as buffers.
-        /// </summary>
-        /// <param name="callback">
-        ///     An <see cref="IOCompletionCallback"/> delegate that represents the callback method
-        ///     invoked when each asynchronous I/O operation completes.
-        /// </param>
-        /// <param name="state">
-        ///     A user-provided object that distinguishes <see cref="NativeOverlapped"/> instance produced from this
-        ///     object from other <see cref="NativeOverlapped"/> instances. Can be <see langword="null"/>.
-        /// </param>
-        /// <param name="pinData">
-        ///     An object or array of objects representing the input or output buffer for the operations. Each
-        ///     object represents a buffer, for example an array of bytes.  Can be <see langword="null"/>.
-        /// </param>
-        /// <remarks>
-        ///     The new <see cref="PreAllocatedOverlapped"/> instance can be passed to
-        ///     <see cref="ThreadPoolBoundHandle.AllocateNativeOverlapped(PreAllocatedOverlapped)"/>, to produce
-        ///     a <see cref="NativeOverlapped"/> instance that can be passed to the operating system in overlapped
-        ///     I/O operations.  A single <see cref="PreAllocatedOverlapped"/> instance can only be used for
-        ///     a single native I/O operation at a time.  However, the state stored in the <see cref="PreAllocatedOverlapped"/>
-        ///     instance can be reused for subsequent native operations. ExecutionContext is not flowed to the invocation
-        ///     of the callback.
-        ///     <note>
-        ///         The buffers specified in <paramref name="pinData"/> are pinned until <see cref="Dispose"/> is called.
-        ///     </note>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="callback"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed.
-        /// </exception>
-        [CLSCompliant(false)]
-        public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
-            UnsafeCreatePortableCore(callback, state, pinData);
-
-        private unsafe PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData, bool flowExecutionContext)
-        {
-            // This construction is duplicated in PreAllocatedOverlapped.Windows.cs
-            // It has to either be duplicated or remove the 'readonly' part of _overlappedPortableCore
-            ArgumentNullException.ThrowIfNull(callback);
-
-            _overlappedPortableCore = new ThreadPoolBoundHandleOverlapped(callback, state, pinData, this, flowExecutionContext);
-        }
-
-        internal bool AddRef() => AddRefPortableCore();
-
-        /// <summary>
-        /// Frees the resources associated with this <see cref="PreAllocatedOverlapped"/> instance.
-        /// </summary>
-        public void Dispose()
-        {
-            DisposePortableCore();
-        }
-
-        internal void Release()
-        {
-            ReleasePortableCore();
-        }
-
-        unsafe void IDeferredDisposable.OnFinalRelease(bool disposed)
-        {
-            IDeferredDisposableOnFinalReleasePortableCore(disposed);
-        }
-    }
-}
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Browser.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.NotSupported.cs
similarity index 100%
rename from src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Browser.cs
rename to src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.NotSupported.cs
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Unix.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Unix.cs
deleted file mode 100644
index 9643edf7f2d8d9..00000000000000
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Unix.cs
+++ /dev/null
@@ -1,255 +0,0 @@
-// Licensed to the .NET Foundation under one or more agreements.
-// The .NET Foundation licenses this file to you under the MIT license.
-
-using System.Diagnostics;
-using System.Runtime.InteropServices;
-
-namespace System.Threading
-{
-    //
-    // Implementation of ThreadPoolBoundHandle that sits on top of the CLR's ThreadPool and Overlapped infrastructure
-    //
-
-    /// <summary>
-    ///     Represents an I/O handle that is bound to the system thread pool and enables low-level
-    ///     components to receive notifications for asynchronous I/O operations.
-    /// </summary>
-    public sealed partial class ThreadPoolBoundHandle : IDisposable
-    {
-        private readonly SafeHandle _handle;
-        private bool _isDisposed;
-
-        private ThreadPoolBoundHandle(SafeHandle handle)
-        {
-            _handle = handle;
-        }
-
-        /// <summary>
-        ///     Gets the bound operating system handle.
-        /// </summary>
-        /// <value>
-        ///     A <see cref="SafeHandle"/> object that holds the bound operating system handle.
-        /// </value>
-        public SafeHandle Handle => _handle;
-
-        /// <summary>
-        ///     Returns a <see cref="ThreadPoolBoundHandle"/> for the specific handle,
-        ///     which is bound to the system thread pool.
-        /// </summary>
-        /// <param name="handle">
-        ///     A <see cref="SafeHandle"/> object that holds the operating system handle. The
-        ///     handle must have been opened for overlapped I/O on the unmanaged side.
-        /// </param>
-        /// <returns>
-        ///     <see cref="ThreadPoolBoundHandle"/> for <paramref name="handle"/>, which
-        ///     is bound to the system thread pool.
-        /// </returns>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="handle"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ArgumentException">
-        ///     <paramref name="handle"/> has been disposed.
-        ///     <para>
-        ///         -or-
-        ///     </para>
-        ///     <paramref name="handle"/> does not refer to a valid I/O handle.
-        ///     <para>
-        ///         -or-
-        ///     </para>
-        ///     <paramref name="handle"/> refers to a handle that has not been opened
-        ///     for overlapped I/O.
-        ///     <para>
-        ///         -or-
-        ///     </para>
-        ///     <paramref name="handle"/> refers to a handle that has already been bound.
-        /// </exception>
-        /// <remarks>
-        ///     This method should be called once per handle.
-        ///     <para>
-        ///         -or-
-        ///     </para>
-        ///     <see cref="ThreadPoolBoundHandle"/> does not take ownership of <paramref name="handle"/>,
-        ///     it remains the responsibility of the caller to call <see cref="SafeHandle.Dispose()"/>.
-        /// </remarks>
-        public static ThreadPoolBoundHandle BindHandle(SafeHandle handle)
-        {
-            ArgumentNullException.ThrowIfNull(handle);
-
-            if (handle.IsClosed || handle.IsInvalid)
-                throw new ArgumentException(SR.Argument_InvalidHandle, nameof(handle));
-
-            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
-        }
-
-        /// <summary>
-        ///     Returns an unmanaged pointer to a <see cref="NativeOverlapped"/> structure, specifying
-        ///     a delegate that is invoked when the asynchronous I/O operation is complete, a user-provided
-        ///     object providing context, and managed objects that serve as buffers.
-        /// </summary>
-        /// <param name="callback">
-        ///     An <see cref="IOCompletionCallback"/> delegate that represents the callback method
-        ///     invoked when the asynchronous I/O operation completes.
-        /// </param>
-        /// <param name="state">
-        ///     A user-provided object that distinguishes this <see cref="NativeOverlapped"/> from other
-        ///     <see cref="NativeOverlapped"/> instances. Can be <see langword="null"/>.
-        /// </param>
-        /// <param name="pinData">
-        ///     An object or array of objects representing the input or output buffer for the operation. Each
-        ///     object represents a buffer, for example an array of bytes.  Can be <see langword="null"/>.
-        /// </param>
-        /// <returns>
-        ///     An unmanaged pointer to a <see cref="NativeOverlapped"/> structure.
-        /// </returns>
-        /// <remarks>
-        ///     <para>
-        ///         The unmanaged pointer returned by this method can be passed to the operating system in
-        ///         overlapped I/O operations. The <see cref="NativeOverlapped"/> structure is fixed in
-        ///         physical memory until <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> is called.
-        ///     </para>
-        ///     <para>
-        ///         The buffer or buffers specified in <paramref name="pinData"/> must be the same as those passed
-        ///         to the unmanaged operating system function that performs the asynchronous I/O.
-        ///     </para>
-        ///     <note>
-        ///         The buffers specified in <paramref name="pinData"/> are pinned for the duration of
-        ///         the I/O operation.
-        ///     </note>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="callback"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed.
-        /// </exception>
-        [CLSCompliant(false)]
-        public unsafe NativeOverlapped* AllocateNativeOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
-            AllocateNativeOverlappedPortableCore(callback, state, pinData);
-
-        /// <summary>
-        ///     Returns an unmanaged pointer to a <see cref="NativeOverlapped"/> structure, specifying
-        ///     a delegate that is invoked when the asynchronous I/O operation is complete, a user-provided
-        ///     object providing context, and managed objects that serve as buffers.
-        /// </summary>
-        /// <param name="callback">
-        ///     An <see cref="IOCompletionCallback"/> delegate that represents the callback method
-        ///     invoked when the asynchronous I/O operation completes.
-        /// </param>
-        /// <param name="state">
-        ///     A user-provided object that distinguishes this <see cref="NativeOverlapped"/> from other
-        ///     <see cref="NativeOverlapped"/> instances. Can be <see langword="null"/>.
-        /// </param>
-        /// <param name="pinData">
-        ///     An object or array of objects representing the input or output buffer for the operation. Each
-        ///     object represents a buffer, for example an array of bytes.  Can be <see langword="null"/>.
-        /// </param>
-        /// <returns>
-        ///     An unmanaged pointer to a <see cref="NativeOverlapped"/> structure.
-        /// </returns>
-        /// <remarks>
-        ///     <para>
-        ///         The unmanaged pointer returned by this method can be passed to the operating system in
-        ///         overlapped I/O operations. The <see cref="NativeOverlapped"/> structure is fixed in
-        ///         physical memory until <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> is called.
-        ///     </para>
-        ///     <para>
-        ///         The buffer or buffers specified in <paramref name="pinData"/> must be the same as those passed
-        ///         to the unmanaged operating system function that performs the asynchronous I/O.
-        ///     </para>
-        ///     <para>
-        ///         <see cref="ExecutionContext"/> is not flowed to the invocation of the callback.
-        ///     </para>
-        ///     <note>
-        ///         The buffers specified in <paramref name="pinData"/> are pinned for the duration of
-        ///         the I/O operation.
-        ///     </note>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="callback"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed.
-        /// </exception>
-        [CLSCompliant(false)]
-        public unsafe NativeOverlapped* UnsafeAllocateNativeOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
-            UnsafeAllocateNativeOverlappedPortableCore(callback, state, pinData);
-
-        /// <summary>
-        ///     Returns an unmanaged pointer to a <see cref="NativeOverlapped"/> structure, using the callback,
-        ///     state, and buffers associated with the specified <see cref="PreAllocatedOverlapped"/> object.
-        /// </summary>
-        /// <param name="preAllocated">
-        ///     A <see cref="PreAllocatedOverlapped"/> object from which to create the NativeOverlapped pointer.
-        /// </param>
-        /// <returns>
-        ///     An unmanaged pointer to a <see cref="NativeOverlapped"/> structure.
-        /// </returns>
-        /// <remarks>
-        ///     <para>
-        ///         The unmanaged pointer returned by this method can be passed to the operating system in
-        ///         overlapped I/O operations. The <see cref="NativeOverlapped"/> structure is fixed in
-        ///         physical memory until <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> is called.
-        ///     </para>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="preAllocated"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ArgumentException">
-        ///     <paramref name="preAllocated"/> is currently in use for another I/O operation.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed, or
-        ///     this method was called after <paramref name="preAllocated"/> was disposed.
-        /// </exception>
-        /// <seealso cref="PreAllocatedOverlapped"/>
-        [CLSCompliant(false)]
-        public unsafe NativeOverlapped* AllocateNativeOverlapped(PreAllocatedOverlapped preAllocated) => AllocateNativeOverlappedPortableCore(preAllocated);
-
-        /// <summary>
-        ///     Frees the unmanaged memory associated with a <see cref="NativeOverlapped"/> structure
-        ///     allocated by the <see cref="AllocateNativeOverlapped"/> method.
-        /// </summary>
-        /// <param name="overlapped">
-        ///     An unmanaged pointer to the <see cref="NativeOverlapped"/> structure to be freed.
-        /// </param>
-        /// <remarks>
-        ///     <note type="caution">
-        ///         You must call the <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> method exactly once
-        ///         on every <see cref="NativeOverlapped"/> unmanaged pointer allocated using the
-        ///         <see cref="AllocateNativeOverlapped"/> method.
-        ///         If you do not call the <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> method, you will
-        ///         leak memory. If you call the <see cref="FreeNativeOverlapped(NativeOverlapped*)"/> method more
-        ///         than once on the same <see cref="NativeOverlapped"/> unmanaged pointer, memory will be corrupted.
-        ///     </note>
-        /// </remarks>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="overlapped"/> is <see langword="null"/>.
-        /// </exception>
-        /// <exception cref="ObjectDisposedException">
-        ///     This method was called after the <see cref="ThreadPoolBoundHandle"/> was disposed.
-        /// </exception>
-        [CLSCompliant(false)]
-        public unsafe void FreeNativeOverlapped(NativeOverlapped* overlapped) => FreeNativeOverlappedPortableCore(overlapped);
-
-        /// <summary>
-        ///     Returns the user-provided object specified when the <see cref="NativeOverlapped"/> instance was
-        ///     allocated using the <see cref="AllocateNativeOverlapped(IOCompletionCallback, object, object)"/>.
-        /// </summary>
-        /// <param name="overlapped">
-        ///     An unmanaged pointer to the <see cref="NativeOverlapped"/> structure from which to return the
-        ///     associated user-provided object.
-        /// </param>
-        /// <returns>
-        ///     A user-provided object that distinguishes this <see cref="NativeOverlapped"/>
-        ///     from other <see cref="NativeOverlapped"/> instances, otherwise, <see langword="null"/> if one was
-        ///     not specified when the instance was allocated using <see cref="AllocateNativeOverlapped"/>.
-        /// </returns>
-        /// <exception cref="ArgumentNullException">
-        ///     <paramref name="overlapped"/> is <see langword="null"/>.
-        /// </exception>
-        [CLSCompliant(false)]
-        public static unsafe object? GetNativeOverlappedState(NativeOverlapped* overlapped) => GetNativeOverlappedStatePortableCore(overlapped);
-
-        public void Dispose() => DisposePortableCore();
-    }
-}

From ba38481349cbfb2db5facaa3f91b2e58d7726b9b Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 03:37:42 +0000
Subject: [PATCH 10/22] UnsafeCreate throws directly; consolidate
 NotSupported.cs into single non-Windows block

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems               | 4 +---
 .../System/Threading/PreAllocatedOverlapped.NotSupported.cs   | 2 +-
 2 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 450cfe01f6ce53..df2fc066cfb7e8 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2871,20 +2871,18 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelLifoSemaphore.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Unix.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.NotSupported.cs" Condition="'$(TargetsWindows)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
-  <ItemGroup Condition="'$(FeatureMultithreading)' != 'true'">
+  <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.NotSupported.cs" />
   </ItemGroup>
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
index 20d3b7aaed01f1..06c413c385890b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
@@ -11,7 +11,7 @@ public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, obje
 
         [CLSCompliant(false)]
         public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
-            new PreAllocatedOverlapped(callback, state, pinData);
+            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
 
         public void Dispose() { }
     }

From 2ca86d5e9ff6438191f35cef24115788c0ebaf1c Mon Sep 17 00:00:00 2001
From: Jan Kotas <jkotas@microsoft.com>
Date: Wed, 18 Mar 2026 21:08:52 -0700
Subject: [PATCH 11/22] Apply suggestion from @jkotas

---
 .../src/System.Private.CoreLib.Shared.projitems                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index df2fc066cfb7e8..c9d1d54d8a0a92 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2878,7 +2878,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>

From 3054412c417dd5bb9d8f656d2963f8acdd5d48f5 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 10:36:49 +0000
Subject: [PATCH 12/22] Move ThreadPoolBoundHandleOverlapped.cs to the
 platform-neutral Windows section

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index c9d1d54d8a0a92..56a7907acf7eb4 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2360,6 +2360,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.WindowsThreadPool.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandle.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WindowsThreadPool.cs" />
@@ -2878,7 +2879,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.Portable.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Portable.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.Windows.cs" Condition="'$(TargetsWindows)' == 'true'" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" Condition="'$(TargetsWindows)' == 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolCallbackWrapper.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>

From a09ca2ab6f994a4d4f327998a2c2390bedbb544e Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 10:43:36 +0000
Subject: [PATCH 13/22] =?UTF-8?q?Rename=20NotSupported.cs=20=E2=86=92=20Pl?=
 =?UTF-8?q?atformNotSupported.cs=20for=20PreAllocatedOverlapped=20and=20Th?=
 =?UTF-8?q?readPoolBoundHandle?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems               | 4 ++--
 ...rted.cs => PreAllocatedOverlapped.PlatformNotSupported.cs} | 0
 ...orted.cs => ThreadPoolBoundHandle.PlatformNotSupported.cs} | 0
 3 files changed, 2 insertions(+), 2 deletions(-)
 rename src/libraries/System.Private.CoreLib/src/System/Threading/{PreAllocatedOverlapped.NotSupported.cs => PreAllocatedOverlapped.PlatformNotSupported.cs} (100%)
 rename src/libraries/System.Private.CoreLib/src/System/Threading/{ThreadPoolBoundHandle.NotSupported.cs => ThreadPoolBoundHandle.PlatformNotSupported.cs} (100%)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 56a7907acf7eb4..3b284717a5f68d 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2883,8 +2883,8 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Backoff.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsWindows)' != 'true'">
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.NotSupported.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.NotSupported.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.PlatformNotSupported.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.PlatformNotSupported.cs" />
   </ItemGroup>
   <ItemGroup Condition="'$(TargetsBrowser)' == 'true' and '$(FeatureMultithreading)' != 'true'">
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Browser.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
similarity index 100%
rename from src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.NotSupported.cs
rename to src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.NotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs
similarity index 100%
rename from src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.NotSupported.cs
rename to src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs

From 7655550fd0820b13c79607c0add98d9a1ac759d9 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 10:51:28 +0000
Subject: [PATCH 14/22] Move PreAllocatedOverlapped.WindowsThreadPool.cs to
 alphabetical position in Windows ItemGroup

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems                 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 3b284717a5f68d..2194ce6d287a93 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -2353,6 +2353,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\EventWaitHandle.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelMonitor.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Mutex.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Thread.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Semaphore.Windows.cs" />
@@ -2361,7 +2362,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandle.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Win32.cs" />

From 4047563466915f8156cdb06d5f802eec72d025e8 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 10:59:33 +0000
Subject: [PATCH 15/22] Move Win32ThreadPoolNativeOverlapped*.cs to
 Windows-only ItemGroup

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems             | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 2194ce6d287a93..f6a1c3564a960d 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -1344,9 +1344,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandle.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandleCannotBeOpenedException.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandleExtensions.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.ExecutionContextCallbackArgs.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.OverlappedData.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\ThreadStaticAttribute.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\ThrowHelper.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeOnly.cs" />
@@ -2363,6 +2360,9 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandle.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.ExecutionContextCallbackArgs.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.OverlappedData.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\TimeZoneInfo.Win32.cs" />
   </ItemGroup>

From e571b213cac41356292568e98a0995700173a626 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 14:11:36 +0000
Subject: [PATCH 16/22] Add Debug.Fail to ThreadPoolBoundHandle private
 constructor in PlatformNotSupported.cs

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs     | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs
index 8e2f33e002f6b7..ab99e8eaad2468 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.PlatformNotSupported.cs
@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics;
 using System.Runtime.InteropServices;
 
 namespace System.Threading
@@ -11,6 +12,7 @@ public sealed class ThreadPoolBoundHandle : IDisposable
 
         private ThreadPoolBoundHandle()
         {
+            Debug.Fail("Unreachable");
         }
 
         public static ThreadPoolBoundHandle BindHandle(SafeHandle handle)

From f77e3c4fc135ff25b5e6404f377df40e31c0aa50 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 14:39:09 +0000
Subject: [PATCH 17/22] Restore working PreAllocatedOverlapped
 constructor/UnsafeCreate on non-Windows to fix test failures

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 ...llocatedOverlapped.PlatformNotSupported.cs | 23 +++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
index 06c413c385890b..b06b6cd43a3713 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
@@ -3,15 +3,30 @@
 
 namespace System.Threading
 {
-    public sealed class PreAllocatedOverlapped : System.IDisposable
+    public sealed class PreAllocatedOverlapped : IDisposable
     {
         [CLSCompliant(false)]
-        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
-            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
+        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) :
+            this(callback, state, pinData, flowExecutionContext: true)
+        {
+        }
 
         [CLSCompliant(false)]
         public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
-            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
+            new PreAllocatedOverlapped(callback, state, pinData, flowExecutionContext: false);
+
+        private unsafe PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData, bool flowExecutionContext)
+        {
+            ArgumentNullException.ThrowIfNull(callback);
+
+            // Validate pinData blittability by packing (this throws ArgumentException for non-blittable types),
+            // then immediately free since overlapped I/O is not supported on this platform.
+            Overlapped overlapped = new Overlapped();
+            NativeOverlapped* nativeOverlapped = flowExecutionContext
+                ? overlapped.Pack(null, pinData)
+                : overlapped.UnsafePack(null, pinData);
+            Overlapped.Free(nativeOverlapped);
+        }
 
         public void Dispose() { }
     }

From 2c54043efc8e529e59b810980a5b883fb2665caa Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 14:52:29 +0000
Subject: [PATCH 18/22] Move DeferredDisposableLifetime.cs to Windows section;
 sort Threading entries alphabetically; fix unused param in
 PlatformNotSupported.cs

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../src/System.Private.CoreLib.Shared.projitems           | 8 ++++----
 .../PreAllocatedOverlapped.PlatformNotSupported.cs        | 2 +-
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index f6a1c3564a960d..ece38286e289a0 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -1264,7 +1264,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\CompressedStack.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Condition.cs" Condition="'$(FeatureMono)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\StackCrawlMark.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\DeferredDisposableLifetime.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\EventResetMode.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\EventWaitHandle.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ExecutionContext.cs" />
@@ -2347,18 +2346,19 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\RuntimeInformation.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Runtime\InteropServices\StandardOleMarshalObject.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Security\SecureString.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\DeferredDisposableLifetime.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\EventWaitHandle.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\LowLevelMonitor.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Mutex.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\PreAllocatedOverlapped.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\RegisteredWaitHandle.WindowsThreadPool.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Thread.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Semaphore.Windows.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.Windows.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.WindowsThreadPool.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Thread.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPool.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandle.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\ThreadPoolBoundHandleOverlapped.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.Windows.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Threading\TimerQueue.WindowsThreadPool.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\WaitHandle.Windows.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Threading\Win32ThreadPoolNativeOverlapped.ExecutionContextCallbackArgs.cs" />
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
index b06b6cd43a3713..fdef98786c1121 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
@@ -15,7 +15,7 @@ public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, obje
         public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
             new PreAllocatedOverlapped(callback, state, pinData, flowExecutionContext: false);
 
-        private unsafe PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData, bool flowExecutionContext)
+        private unsafe PreAllocatedOverlapped(IOCompletionCallback callback, object? _, object? pinData, bool flowExecutionContext)
         {
             ArgumentNullException.ThrowIfNull(callback);
 

From ffce285e48ed9ea90e33a075aee1fe9a6b938991 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 15:04:46 +0000
Subject: [PATCH 19/22] Simplify
 PreAllocatedOverlapped.PlatformNotSupported.cs; mark tests Windows-only

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 ...llocatedOverlapped.PlatformNotSupported.cs | 21 +++----------------
 ...BoundHandle_PreAllocatedOverlappedTests.cs | 11 +++++++++-
 2 files changed, 13 insertions(+), 19 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
index fdef98786c1121..b6199abd0f066e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
@@ -6,27 +6,12 @@ namespace System.Threading
     public sealed class PreAllocatedOverlapped : IDisposable
     {
         [CLSCompliant(false)]
-        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) :
-            this(callback, state, pinData, flowExecutionContext: true)
-        {
-        }
+        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
+            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
 
         [CLSCompliant(false)]
         public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
-            new PreAllocatedOverlapped(callback, state, pinData, flowExecutionContext: false);
-
-        private unsafe PreAllocatedOverlapped(IOCompletionCallback callback, object? _, object? pinData, bool flowExecutionContext)
-        {
-            ArgumentNullException.ThrowIfNull(callback);
-
-            // Validate pinData blittability by packing (this throws ArgumentException for non-blittable types),
-            // then immediately free since overlapped I/O is not supported on this platform.
-            Overlapped overlapped = new Overlapped();
-            NativeOverlapped* nativeOverlapped = flowExecutionContext
-                ? overlapped.Pack(null, pinData)
-                : overlapped.UnsafePack(null, pinData);
-            Overlapped.Free(nativeOverlapped);
-        }
+            throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
 
         public void Dispose() { }
     }
diff --git a/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs b/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
index 728732326e5bae..678908a1bcb7e9 100644
--- a/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
+++ b/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
@@ -9,7 +9,7 @@
 public partial class ThreadPoolBoundHandleTests
 {
     [Fact]
-    [ActiveIssue("https://github.com/mono/mono/issues/15313", TestRuntimes.Mono)]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_NullAsCallback_ThrowsArgumentNullException()
     {
         AssertExtensions.Throws<ArgumentNullException>("callback", () => new PreAllocatedOverlapped(null, new object(), new byte[256]));
@@ -21,6 +21,7 @@ public unsafe void PreAllocatedOverlapped_NullAsCallback_ThrowsArgumentNullExcep
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_NullAsContext_DoesNotThrow()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, (object)null, new byte[256])) { }
@@ -28,6 +29,7 @@ public unsafe void PreAllocatedOverlapped_NullAsContext_DoesNotThrow()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_NullAsPinData_DoesNotThrow()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, new object(), (byte[])null)) { }
@@ -35,6 +37,7 @@ public unsafe void PreAllocatedOverlapped_NullAsPinData_DoesNotThrow()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_EmptyArrayAsPinData_DoesNotThrow()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, new object(), new byte[0])) { }
@@ -42,6 +45,7 @@ public unsafe void PreAllocatedOverlapped_EmptyArrayAsPinData_DoesNotThrow()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     [ActiveIssue("https://github.com/mono/mono/issues/15313", TestRuntimes.Mono)]
     public unsafe void PreAllocatedOverlapped_NonBlittableTypeAsPinData_Throws()
     {
@@ -54,6 +58,7 @@ public unsafe void PreAllocatedOverlapped_NonBlittableTypeAsPinData_Throws()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_BlittableTypeAsPinData_DoesNotThrow()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, new object(), new BlittableType() { i = 42 })) { }
@@ -61,6 +66,7 @@ public unsafe void PreAllocatedOverlapped_BlittableTypeAsPinData_DoesNotThrow()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_ObjectArrayAsPinData_DoesNotThrow()
     {
         var array = new object[]
@@ -74,6 +80,7 @@ public unsafe void PreAllocatedOverlapped_ObjectArrayAsPinData_DoesNotThrow()
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     [ActiveIssue("https://github.com/mono/mono/issues/15313", TestRuntimes.Mono)]
     public unsafe void PreAllocatedOverlapped_ObjectArrayWithNonBlittableTypeAsPinData_Throws()
     {
@@ -92,6 +99,7 @@ public unsafe void PreAllocatedOverlapped_ObjectArrayWithNonBlittableTypeAsPinDa
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_ReturnedNativeOverlapped_InternalLowAndInternalHighSetToZero()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, new object(), new byte[256])) { }
@@ -99,6 +107,7 @@ public unsafe void PreAllocatedOverlapped_ReturnedNativeOverlapped_InternalLowAn
     }
 
     [Fact]
+    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_ReturnedNativeOverlapped_OffsetLowAndOffsetHighSetToZero()
     {
         using (new PreAllocatedOverlapped((_, __, ___) => { }, new object(), new byte[256])) { }

From 978de782adb074a4606ed39aa9b731d3eef8494f Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 17:35:20 +0000
Subject: [PATCH 20/22] Add argument validation to
 PreAllocatedOverlapped.PlatformNotSupported.cs; re-enable NullAsCallback test

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../PreAllocatedOverlapped.PlatformNotSupported.cs     | 10 ++++++++--
 ...hreadPoolBoundHandle_PreAllocatedOverlappedTests.cs |  1 -
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
index b6199abd0f066e..5ce63f8a8736c7 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/PreAllocatedOverlapped.PlatformNotSupported.cs
@@ -6,12 +6,18 @@ namespace System.Threading
     public sealed class PreAllocatedOverlapped : IDisposable
     {
         [CLSCompliant(false)]
-        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData) =>
+        public PreAllocatedOverlapped(IOCompletionCallback callback, object? state, object? pinData)
+        {
+            ArgumentNullException.ThrowIfNull(callback);
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
+        }
 
         [CLSCompliant(false)]
-        public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData) =>
+        public static PreAllocatedOverlapped UnsafeCreate(IOCompletionCallback callback, object? state, object? pinData)
+        {
+            ArgumentNullException.ThrowIfNull(callback);
             throw new PlatformNotSupportedException(SR.PlatformNotSupported_OverlappedIO);
+        }
 
         public void Dispose() { }
     }
diff --git a/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs b/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
index 678908a1bcb7e9..0a116f2d0d33fd 100644
--- a/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
+++ b/src/libraries/System.Threading.Overlapped/tests/ThreadPoolBoundHandle_PreAllocatedOverlappedTests.cs
@@ -9,7 +9,6 @@
 public partial class ThreadPoolBoundHandleTests
 {
     [Fact]
-    [PlatformSpecific(TestPlatforms.Windows)] // PreAllocatedOverlapped is not supported on non-Windows
     public unsafe void PreAllocatedOverlapped_NullAsCallback_ThrowsArgumentNullException()
     {
         AssertExtensions.Throws<ArgumentNullException>("callback", () => new PreAllocatedOverlapped(null, new object(), new byte[256]));

From 8b9f2b24afc2dd42d4d7d47d3a52343ae5d6a1a2 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 18:13:10 +0000
Subject: [PATCH 21/22] Remove incorrectly applied [RequiresUnsafe] from
 AllocateNativeOverlapped* methods

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../System.Private.CoreLib/src/System/Threading/Overlapped.cs | 1 -
 .../src/System/Threading/ThreadPoolBoundHandle.Portable.cs    | 4 ----
 2 files changed, 5 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
index 423e9429b33be0..f06c8f52ef5c6b 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
@@ -134,7 +134,6 @@ public static void Free(NativeOverlapped* nativeOverlappedPtr)
             FreeNativeOverlapped(nativeOverlappedPtr);
         }
 
-        [RequiresUnsafe]
         private NativeOverlapped* AllocateNativeOverlapped(object? userData)
         {
             NativeOverlapped* pNativeOverlapped = null;
diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Portable.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Portable.cs
index 60a9c1848cc243..030092d9d6e16e 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Portable.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/ThreadPoolBoundHandle.Portable.cs
@@ -17,15 +17,12 @@ namespace System.Threading
     /// </summary>
     public sealed partial class ThreadPoolBoundHandle : IDisposable
     {
-        [RequiresUnsafe]
         private unsafe NativeOverlapped* AllocateNativeOverlappedPortableCore(IOCompletionCallback callback, object? state, object? pinData) =>
             AllocateNativeOverlappedPortableCore(callback, state, pinData, flowExecutionContext: true);
 
-        [RequiresUnsafe]
         private unsafe NativeOverlapped* UnsafeAllocateNativeOverlappedPortableCore(IOCompletionCallback callback, object? state, object? pinData) =>
             AllocateNativeOverlappedPortableCore(callback, state, pinData, flowExecutionContext: false);
 
-        [RequiresUnsafe]
         private unsafe NativeOverlapped* AllocateNativeOverlappedPortableCore(IOCompletionCallback callback, object? state, object? pinData, bool flowExecutionContext)
         {
             ArgumentNullException.ThrowIfNull(callback);
@@ -36,7 +33,6 @@ public sealed partial class ThreadPoolBoundHandle : IDisposable
             return overlapped._nativeOverlapped;
         }
 
-        [RequiresUnsafe]
         private unsafe NativeOverlapped* AllocateNativeOverlappedPortableCore(PreAllocatedOverlapped preAllocated)
         {
             ArgumentNullException.ThrowIfNull(preAllocated);

From 6d73dd9a9b4aa2f95ed87433de681e02bbcbabd0 Mon Sep 17 00:00:00 2001
From: "copilot-swe-agent[bot]" <198982749+Copilot@users.noreply.github.com>
Date: Thu, 19 Mar 2026 18:21:48 +0000
Subject: [PATCH 22/22] Remove [RequiresUnsafe] annotations from
 Overlapped.Pack and UnsafePack

Co-authored-by: jkotas <6668460+jkotas@users.noreply.github.com>
---
 .../System.Private.CoreLib/src/System/Threading/Overlapped.cs | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs b/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
index f06c8f52ef5c6b..13b8eec743e5fc 100644
--- a/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Threading/Overlapped.cs
@@ -68,12 +68,10 @@ public IntPtr EventHandleIntPtr
 
         [Obsolete("This overload is not safe and has been deprecated. Use Pack(IOCompletionCallback?, object?) instead.")]
         [CLSCompliant(false)]
-        [RequiresUnsafe]
         public NativeOverlapped* Pack(IOCompletionCallback? iocb)
             => Pack(iocb, null);
 
         [CLSCompliant(false)]
-        [RequiresUnsafe]
         public NativeOverlapped* Pack(IOCompletionCallback? iocb, object? userData)
         {
             if (_pNativeOverlapped != null)
@@ -95,12 +93,10 @@ public IntPtr EventHandleIntPtr
 
         [Obsolete("This overload is not safe and has been deprecated. Use UnsafePack(IOCompletionCallback?, object?) instead.")]
         [CLSCompliant(false)]
-        [RequiresUnsafe]
         public NativeOverlapped* UnsafePack(IOCompletionCallback? iocb)
             => UnsafePack(iocb, null);
 
         [CLSCompliant(false)]
-        [RequiresUnsafe]
         public NativeOverlapped* UnsafePack(IOCompletionCallback? iocb, object? userData)
         {
             if (_pNativeOverlapped != null)