fix(lmxproxy): use raw Win32 message pump instead of WinForms Application.Run

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/MxAccess/StaComThread.cs

@@ -1,24 +1,29 @@
 using System;
+using System.Collections.Concurrent;
+using System.Runtime.InteropServices;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Windows.Forms;
 using Serilog;
 
 namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
 {
     /// <summary>
-    ///     Dedicated STA thread with a Windows message pump for COM interop.
+    ///     Dedicated STA thread with a raw Win32 message pump for COM interop.
     ///     All MxAccess COM objects must be created and called on this thread
     ///     so that COM callbacks (OnDataChange, OnWriteComplete) are delivered
     ///     via the message loop.
     /// </summary>
     public sealed class StaComThread : IDisposable
     {
+        private const uint WM_APP = 0x8000;
+        private const uint PM_NOREMOVE = 0x0000;
+
         private static readonly ILogger Log = Serilog.Log.ForContext<StaComThread>();
 
         private readonly Thread _thread;
         private readonly TaskCompletionSource<bool> _ready = new TaskCompletionSource<bool>();
-        private SynchronizationContext _syncContext = null!;
+        private readonly ConcurrentQueue<Action> _workItems = new ConcurrentQueue<Action>();
+        private volatile uint _nativeThreadId;
         private bool _disposed;
 
         public StaComThread()
@@ -50,7 +55,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
             if (_disposed) throw new ObjectDisposedException(nameof(StaComThread));
 
             var tcs = new TaskCompletionSource<bool>();
-            _syncContext.Post(_ =>
+            _workItems.Enqueue(() =>
             {
                 try
                 {
@@ -61,7 +66,8 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
                 {
                     tcs.TrySetException(ex);
                 }
-            }, null);
+            });
+            PostThreadMessage(_nativeThreadId, WM_APP, IntPtr.Zero, IntPtr.Zero);
             return tcs.Task;
         }
 
@@ -74,7 +80,7 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
             if (_disposed) throw new ObjectDisposedException(nameof(StaComThread));
 
             var tcs = new TaskCompletionSource<T>();
-            _syncContext.Post(_ =>
+            _workItems.Enqueue(() =>
             {
                 try
                 {
@@ -84,7 +90,8 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
                 {
                     tcs.TrySetException(ex);
                 }
-            }, null);
+            });
+            PostThreadMessage(_nativeThreadId, WM_APP, IntPtr.Zero, IntPtr.Zero);
             return tcs.Task;
         }
 
@@ -95,8 +102,8 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
 
             try
             {
-                // Post Application.ExitThread to break out of the message loop
+                if (_nativeThreadId != 0)
-                _syncContext?.Post(_ => Application.ExitThread(), null);
+                    PostThreadMessage(_nativeThreadId, WM_APP + 1, IntPtr.Zero, IntPtr.Zero);
                 _thread.Join(TimeSpan.FromSeconds(5));
             }
             catch (Exception ex)
@@ -111,17 +118,33 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
         {
             try
             {
-                // Install a WindowsFormsSynchronizationContext so that
+                _nativeThreadId = GetCurrentThreadId();
-                // Post/Send dispatches onto this thread's message loop
+
-                Application.OleRequired();
+                // Force message queue creation by peeking
-                var ctx = new WindowsFormsSynchronizationContext();
+                MSG msg;
-                SynchronizationContext.SetSynchronizationContext(ctx);
+                PeekMessage(out msg, IntPtr.Zero, 0, 0, PM_NOREMOVE);
-                _syncContext = ctx;
 
                 _ready.TrySetResult(true);
 
-                // Run the message loop — this blocks until Application.ExitThread()
+                // Run the message loop — blocks until WM_QUIT
-                Application.Run();
+                while (GetMessage(out msg, IntPtr.Zero, 0, 0) > 0)
+                {
+                    if (msg.message == WM_APP)
+                    {
+                        DrainQueue();
+                    }
+                    else if (msg.message == WM_APP + 1)
+                    {
+                        // Shutdown signal — drain remaining work then quit
+                        DrainQueue();
+                        PostQuitMessage(0);
+                    }
+                    else
+                    {
+                        TranslateMessage(ref msg);
+                        DispatchMessage(ref msg);
+                    }
+                }
             }
             catch (Exception ex)
             {
@@ -129,5 +152,66 @@ namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
                 _ready.TrySetException(ex);
             }
         }
+
+        private void DrainQueue()
+        {
+            while (_workItems.TryDequeue(out var workItem))
+            {
+                try
+                {
+                    workItem();
+                }
+                catch (Exception ex)
+                {
+                    Log.Error(ex, "Unhandled exception in STA work item");
+                }
+            }
+        }
+
+        #region Win32 PInvoke
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct MSG
+        {
+            public IntPtr hwnd;
+            public uint message;
+            public IntPtr wParam;
+            public IntPtr lParam;
+            public uint time;
+            public POINT pt;
+        }
+
+        [StructLayout(LayoutKind.Sequential)]
+        private struct POINT
+        {
+            public int x;
+            public int y;
+        }
+
+        [DllImport("user32.dll")]
+        private static extern int GetMessage(out MSG lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax);
+
+        [DllImport("user32.dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        private static extern bool TranslateMessage(ref MSG lpMsg);
+
+        [DllImport("user32.dll")]
+        private static extern IntPtr DispatchMessage(ref MSG lpMsg);
+
+        [DllImport("user32.dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        private static extern bool PostThreadMessage(uint idThread, uint Msg, IntPtr wParam, IntPtr lParam);
+
+        [DllImport("user32.dll")]
+        private static extern void PostQuitMessage(int nExitCode);
+
+        [DllImport("user32.dll")]
+        [return: MarshalAs(UnmanagedType.Bool)]
+        private static extern bool PeekMessage(out MSG lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax, uint wRemoveMsg);
+
+        [DllImport("kernel32.dll")]
+        private static extern uint GetCurrentThreadId();
+
+        #endregion
     }
 }

lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/ZB.MOM.WW.LmxProxy.Host.csproj

@@ -42,7 +42,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <Reference Include="System.Windows.Forms" />
     <Reference Include="ArchestrA.MXAccess">
       <HintPath>..\..\lib\ArchestrA.MXAccess.dll</HintPath>
       <Private>true</Private>