From f6ea9a8c465380cfbcf00c2a8640b2e4664d99d7 Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Sat, 29 May 2021 13:50:35 -0400
Subject: [PATCH 1/2] Always spawn message loop thread for SystemEvents

---
 .../src/Microsoft/Win32/SystemEvents.cs       | 40 +++++++------------
 .../Microsoft.Win32.SystemEvents.Tests.csproj |  1 +
 .../SystemEvents.InvokeOnEventsThread.cs      | 30 ++++++++++++--
 3 files changed, 43 insertions(+), 28 deletions(-)

diff --git a/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft/Win32/SystemEvents.cs b/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft/Win32/SystemEvents.cs
index 374070553e433..077e5fa1ad841 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft/Win32/SystemEvents.cs
+++ b/src/libraries/Microsoft.Win32.SystemEvents/src/Microsoft/Win32/SystemEvents.cs
@@ -469,33 +469,23 @@ private static void EnsureSystemEvents(bool requireHandle)
                 {
                     if (s_systemEvents == null)
                     {
-                        // If we are creating system events on a thread declared as STA, then
-                        // just share the thread.
-                        if (!UserInteractive || Thread.CurrentThread.GetApartmentState() == ApartmentState.STA)
-                        {
-                            SystemEvents systemEvents = new SystemEvents();
-                            systemEvents.Initialize();
+                        // Create a new pumping thread.  We always create one even if the current thread
+                        // is STA, as there are no guarantees this thread will pump nor still be alive
+                        // for the desired duration.
 
-                            // ensure this is initialized last as that will force concurrent threads calling
-                            // this method to block until after we've initialized.
-                            s_systemEvents = systemEvents;
-                        }
-                        else
+                        s_eventWindowReady = new ManualResetEvent(false);
+                        SystemEvents systemEvents = new SystemEvents();
+                        s_windowThread = new Thread(new ThreadStart(systemEvents.WindowThreadProc))
                         {
-                            s_eventWindowReady = new ManualResetEvent(false);
-                            SystemEvents systemEvents = new SystemEvents();
-                            s_windowThread = new Thread(new ThreadStart(systemEvents.WindowThreadProc))
-                            {
-                                IsBackground = true,
-                                Name = ".NET System Events"
-                            };
-                            s_windowThread.Start();
-                            s_eventWindowReady.WaitOne();
-
-                            // ensure this is initialized last as that will force concurrent threads calling
-                            // this method to block until after we've initialized.
-                            s_systemEvents = systemEvents;
-                        }
+                            IsBackground = true,
+                            Name = ".NET System Events"
+                        };
+                        s_windowThread.Start();
+                        s_eventWindowReady.WaitOne();
+
+                        // ensure this is initialized last as that will force concurrent threads calling
+                        // this method to block until after we've initialized.
+                        s_systemEvents = systemEvents;
 
                         if (requireHandle && s_systemEvents._windowHandle == IntPtr.Zero)
                         {
diff --git a/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj b/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
index c8efc5731d0d2..4ccc4b8d8845d 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
+++ b/src/libraries/Microsoft.Win32.SystemEvents/tests/Microsoft.Win32.SystemEvents.Tests.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent)-windows;net461-windows</TargetFrameworks>
+    <IncludeRemoteExecutor>true</IncludeRemoteExecutor>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="$(CommonPath)Interop\Windows\Interop.Libraries.cs"
diff --git a/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs b/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
index aad5c99b8b64b..1074224ebcf0a 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
+++ b/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
@@ -2,10 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Runtime.InteropServices;
 using System.Threading;
+using Microsoft.DotNet.RemoteExecutor;
 using Xunit;
 using static Interop;
 
@@ -53,5 +51,31 @@ public void InvokeOnEventsThreadRunsOnSameThreadAsOtherEvents()
                 invoked.Dispose();
             }
         }
+
+        [ConditionalFact(typeof(PlatformDetection), nameof(PlatformDetection.IsNotWindowsNanoNorServerCore))]
+        [SkipOnTargetFramework(TargetFrameworkMonikers.NetFramework)]
+        public void RegisterFromSTAThreadThatGoesAway_MessageStillDelivered()
+        {
+            RemoteExecutor.Invoke(() => // to ensure no one has registered for any events before
+            {
+                bool changing = false, changed = false;
+
+                // Register for the events on an STA thread that then immediately exits
+                var thread = new Thread(() =>
+                {
+                    SystemEvents.DisplaySettingsChanging += (o, e) => changing = true;
+                    SystemEvents.DisplaySettingsChanged += (o, e) => changed = true;
+                });
+                thread.SetApartmentState(ApartmentState.STA);
+                thread.IsBackground = true;
+                thread.Start();
+                thread.Join();
+
+                SendMessage(User32.WM_REFLECT + User32.WM_DISPLAYCHANGE, IntPtr.Zero, IntPtr.Zero);
+
+                Assert.True(changing);
+                Assert.True(changed);
+            });
+        }
     }
 }

From 260b3273143c2c08520d135350acade61d568bcb Mon Sep 17 00:00:00 2001
From: Stephen Toub <stoub@microsoft.com>
Date: Sat, 29 May 2021 19:34:33 -0400
Subject: [PATCH 2/2] Update
 src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs

Co-authored-by: Jan Kotas <jkotas@microsoft.com>
---
 .../tests/SystemEvents.InvokeOnEventsThread.cs                   | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs b/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
index 1074224ebcf0a..b665f5c5d7f5a 100644
--- a/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
+++ b/src/libraries/Microsoft.Win32.SystemEvents/tests/SystemEvents.InvokeOnEventsThread.cs
@@ -67,7 +67,6 @@ public void RegisterFromSTAThreadThatGoesAway_MessageStillDelivered()
                     SystemEvents.DisplaySettingsChanged += (o, e) => changed = true;
                 });
                 thread.SetApartmentState(ApartmentState.STA);
-                thread.IsBackground = true;
                 thread.Start();
                 thread.Join();