Experiment with a winform-based msg pump.

samples/WinForm32/Form1.cs

@@ -18,6 +18,8 @@ namespace WinFormSample
 {
   public partial class Form1 : Form
   {
+    bool useDiyPump = true;
+    MessagePumpThread pump;
     TwainAppSession twain;
     readonly string saveFolder;
     readonly Stopwatch watch = new();
@@ -34,9 +36,10 @@ namespace WinFormSample
       var libVer = FileVersionInfo.GetVersionInfo(typeof(TwainAppSession).Assembly.Location).ProductVersion;
       Text += $"{(TWPlatform.Is32bit ? " 32bit" : " 64bit")} on NTwain {libVer}";
 
+      pump = new MessagePumpThread();
       TWPlatform.PreferLegacyDSM = false;
 
-      twain = new TwainAppSession(SynchronizationContext.Current!, Assembly.GetExecutingAssembly().Location);
+      twain = new TwainAppSession(Assembly.GetExecutingAssembly().Location);
       twain.StateChanged += Twain_StateChanged;
       twain.DefaultSourceChanged += Twain_DefaultSourceChanged;
       twain.CurrentSourceChanged += Twain_CurrentSourceChanged;
@@ -62,11 +65,14 @@ namespace WinFormSample
 
     private void Twain_SourceDisabled(TwainAppSession sender, TW_IDENTITY_LEGACY e)
     {
-      if (watch.IsRunning)
+      BeginInvoke(() =>
       {
-        watch.Stop();
-        MessageBox.Show($"Took {watch.Elapsed} to finish that transfer.");
-      }
+        if (watch.IsRunning)
+        {
+          watch.Stop();
+          MessageBox.Show($"Took {watch.Elapsed} to finish that transfer.");
+        }
+      });
     }
 
     private void SystemEvents_SessionSwitch(object sender, SessionSwitchEventArgs e)
@@ -85,18 +91,31 @@ namespace WinFormSample
     {
       base.OnHandleCreated(e);
 
-
-      var hwnd = this.Handle;
-      var rc = twain.OpenDSM(hwnd);
-      twain.AddWinformFilter();
-      Debug.WriteLine($"OpenDSM={rc}");
+      if (useDiyPump)
+      {
+        _ = pump.AttachAsync(twain);
+      }
+      else
+      {
+        var hwnd = this.Handle;
+        var rc = twain.OpenDSM(hwnd, SynchronizationContext.Current!);
+        twain.AddWinformFilter();
+        Debug.WriteLine($"OpenDSM={rc}");
+      }
     }
 
     protected override void OnClosing(CancelEventArgs e)
     {
-      var finalState = twain.TryStepdown(STATE.S2);
-      Debug.WriteLine($"Stepdown result state={finalState}");
-      twain.RemoveWinformFilter();
+      if (useDiyPump)
+      {
+        pump.Detatch();
+      }
+      else
+      {
+        var finalState = twain.TryStepdown(STATE.S2);
+        Debug.WriteLine($"Stepdown result state={finalState}");
+        twain.RemoveWinformFilter();
+      }
       base.OnClosing(e);
     }
 
@@ -214,39 +233,42 @@ namespace WinFormSample
 
     private void Twain_DefaultSourceChanged(TwainAppSession sender, TW_IDENTITY_LEGACY ds)
     {
-      lblDefault.Text = ds.ProductName;
+      BeginInvoke(() => lblDefault.Text = ds.ProductName);
     }
 
     private void Twain_StateChanged(TwainAppSession sender, STATE state)
     {
-      Invoke(() => lblState.Text = state.ToString());
+      BeginInvoke(() => lblState.Text = state.ToString());
     }
 
     private void Twain_CurrentSourceChanged(TwainAppSession sender, TW_IDENTITY_LEGACY ds)
     {
-      lblCurrent.Text = ds.ToString();
-      if (twain.State == STATE.S4)
+      BeginInvoke(() =>
       {
-        LoadCapInfoList();
+        lblCurrent.Text = ds.ToString();
+        if (twain.State == STATE.S4)
+        {
+          LoadCapInfoList();
 
-        // never seen a driver support these but here it is to test it
-        if (twain.GetCapLabel(CAP.ICAP_SUPPORTEDSIZES, out string? test).RC == TWRC.SUCCESS)
-        {
-          Debug.WriteLine($"Supported sizes label from ds = {test}");
+          // never seen a driver support these but here it is to test it
+          if (twain.GetCapLabel(CAP.ICAP_SUPPORTEDSIZES, out string? test).RC == TWRC.SUCCESS)
+          {
+            Debug.WriteLine($"Supported sizes label from ds = {test}");
+          }
+          if (twain.GetCapHelp(CAP.ICAP_SUPPORTEDSIZES, out string? test2).RC == TWRC.SUCCESS)
+          {
+            Debug.WriteLine($"Supported sizes help from ds = {test2}");
+          }
+          if (twain.GetCapLabelEnum(CAP.ICAP_SUPPORTEDSIZES, out IList<string>? test3).RC == TWRC.SUCCESS && test3 != null)
+          {
+            Debug.WriteLine($"Supported sizes label enum from ds = {string.Join(Environment.NewLine, test3)}");
+          }
         }
-        if (twain.GetCapHelp(CAP.ICAP_SUPPORTEDSIZES, out string? test2).RC == TWRC.SUCCESS)
+        else
         {
-          Debug.WriteLine($"Supported sizes help from ds = {test2}");
+          capListView.Items.Clear();
         }
-        if (twain.GetCapLabelEnum(CAP.ICAP_SUPPORTEDSIZES, out IList<string>? test3).RC == TWRC.SUCCESS && test3 != null)
-        {
-          Debug.WriteLine($"Supported sizes label enum from ds = {string.Join(Environment.NewLine, test3)}");
-        }
-      }
-      else
-      {
-        capListView.Items.Clear();
-      }
+      });
     }
 
     private void LoadCapInfoList()

samples/WinForm32/Program.cs

@@ -16,14 +16,14 @@ namespace WinFormSample
     [STAThread]
     static void Main()
     {
-      if (DsmLoader.TryUseCustomDSM())
-      {
-        Debug.WriteLine("Using our own dsm now :)");
-      }
-      else
-      {
-        Debug.WriteLine("Will attempt to use default dsm :(");
-      }
+      //if (DsmLoader.TryUseCustomDSM())
+      //{
+      //  Debug.WriteLine("Using our own dsm now :)");
+      //}
+      //else
+      //{
+      //  Debug.WriteLine("Will attempt to use default dsm :(");
+      //}
 
       // To customize application configuration such as set high DPI settings or default font,
       // see https://aka.ms/applicationconfiguration.

src/NTwain/DSM/DsmLoader.cs

@@ -1,6 +1,7 @@
 using NTwain.Data;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Reflection;
@@ -8,7 +9,7 @@ using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading.Tasks;
 
-namespace WinFormSample
+namespace NTwain.DSM
 {
   /// <summary>
   /// For demoing loading dsm from custom path in case
@@ -19,15 +20,26 @@ namespace WinFormSample
   {
     static IntPtr __dllPtr;
 
-    public static bool TryUseCustomDSM()
+    public static bool TryLoadCustomDSM()
     {
       if (__dllPtr == IntPtr.Zero)
       {
+        var curFile = Assembly.GetExecutingAssembly().Location;
+
         var dll = Path.Combine(
-          Path.GetDirectoryName(Environment.ProcessPath ?? Assembly.GetExecutingAssembly().Location)!,
+          Path.GetDirectoryName(curFile)!,
           $@"runtimes\win-{(TWPlatform.Is32bit ? "x86" : "x64")}\native\TWAINDSM.dll");
 
         __dllPtr = LoadLibraryW(dll);
+
+        if (__dllPtr != IntPtr.Zero)
+        {
+          Debug.WriteLine("Using our own dsm now :)");
+        }
+        else
+        {
+          Debug.WriteLine("Will attempt to use default dsm :(");
+        }
       }
       return __dllPtr != IntPtr.Zero;
     }

src/NTwain/Data/TWAINH_EXTRAS.cs

@@ -660,7 +660,7 @@ namespace NTwain.Data
     /// <summary>
     /// A simplified check on whether this has valid data from DSM.
     /// </summary>
-    public bool HasValue => Id == 0 && ProtocolMajor == 0 && ProtocolMinor == 0;
+    public bool HasValue => Id != 0 && ProtocolMajor != 0 && ProtocolMinor != 0;
 
     public override string ToString()
     {

src/NTwain/MessagePumpThread.cs

@@ -0,0 +1,100 @@
+#if WINDOWS || NETFRAMEWORK
+using NTwain.Data;
+using System;
+using System.Diagnostics;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Windows.Forms;
+
+namespace NTwain
+{
+  /// <summary>
+  /// For use under Windows to host a message pump in non-winform/wpf apps.
+  /// This is highly experimental.
+  /// </summary>
+  public class MessagePumpThread
+  {
+    DummyForm? _dummyForm;
+    TwainAppSession? _twain;
+
+    public bool IsRunning => _dummyForm != null && _dummyForm.IsHandleCreated;
+
+    /// <summary>
+    /// Starts the thread, attaches a twain session to it,
+    /// and opens the DSM.
+    /// </summary>
+    /// <param name="twain"></param>
+    /// <returns></returns>
+    /// <exception cref="InvalidOperationException"></exception>
+    public async Task<STS> AttachAsync(TwainAppSession twain)
+    {
+      if (twain.State > STATE.S2) throw new InvalidOperationException("Cannot attach to an opened TWAIN session.");
+      if (_twain != null || _dummyForm != null) throw new InvalidOperationException("Already attached previously.");
+
+      Thread t = new(RunMessagePump);
+      t.IsBackground = true;
+      t.SetApartmentState(ApartmentState.STA);
+      t.Start();
+
+      while (_dummyForm == null || !_dummyForm.IsHandleCreated)
+      {
+        await Task.Delay(100);
+      }
+
+      STS sts = default;
+      ManualResetEventSlim evt = new();
+      _dummyForm.BeginInvoke(() =>
+      {
+        sts = twain.OpenDSM(_dummyForm.Handle, SynchronizationContext.Current!);
+        if (sts.IsSuccess)
+        {
+          twain.AddWinformFilter();
+          _twain = twain;
+        }
+        evt.Set();
+      });
+      evt.Wait();
+      return sts;
+    }
+
+    /// <summary>
+    /// Detatches a previously attached session and stops the thread.
+    /// </summary>
+    public void Detatch()
+    {
+      if (_dummyForm != null && _twain != null)
+      {
+        _dummyForm.BeginInvoke(_dummyForm.Close);
+      }
+    }
+
+    void RunMessagePump()
+    {
+      Debug.WriteLine("TWAIN pump thread starting");
+      _dummyForm = new DummyForm();
+      _dummyForm.FormClosed += (s, e) =>
+      {
+        if (_twain != null)
+        {
+          _twain.TryStepdown(STATE.S4);
+          _twain.RemoveWinformFilter();
+          _twain.CloseDSM();
+          _twain = null;
+        }
+        _dummyForm = null;
+      };
+      Application.Run(_dummyForm);
+      Debug.WriteLine("TWAIN pump thread ended");
+    }
+
+    class DummyForm : Form
+    {
+      public DummyForm()
+      {
+        ShowInTaskbar = false;
+        WindowState = FormWindowState.Minimized;
+      }
+    }
+  }
+}
+#endif

src/NTwain/NTwain.csproj

@@ -21,6 +21,18 @@
   <ItemGroup Condition=" '$(TargetFramework)' != 'net462'">
     <PackageReference Include="System.Text.Encoding.CodePages" Version="7.0.0" />
   </ItemGroup>
+  <ItemGroup>
+    <None Remove="runtimes\win-x64\native\TWAINDSM.dll" />
+    <None Remove="runtimes\win-x86\native\TWAINDSM.dll" />
+  </ItemGroup>
+  <ItemGroup>
+    <Content Include="runtimes\win-x64\native\TWAINDSM.dll">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+    <Content Include="runtimes\win-x86\native\TWAINDSM.dll">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
   
   <ItemGroup>
     <None Update="DSM\DSMGenerator.dummy">

src/NTwain/Native/WinNativeMethods.cs

@@ -55,5 +55,43 @@ namespace NTwain.Native
       GPTR = GMEM_FIXED | GMEM_ZEROINIT,
       GHND = GMEM_MOVEABLE | GMEM_ZEROINIT
     }
+
+//    [Flags]
+//    public enum PEEK_MESSAGE_REMOVE_TYPE : uint
+//    {
+//      PM_NOREMOVE = 0x00000000,
+//      PM_REMOVE = 0x00000001,
+//      PM_NOYIELD = 0x00000002,
+//      PM_QS_INPUT = 0x04070000,
+//      PM_QS_POSTMESSAGE = 0x00980000,
+//      PM_QS_PAINT = 0x00200000,
+//      PM_QS_SENDMESSAGE = 0x00400000,
+//    }
+
+//#if NET7_0_OR_GREATER
+//    [LibraryImport("USER32.dll")]
+//    public static partial int PeekMessageW(ref WIN_MESSAGE lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax, PEEK_MESSAGE_REMOVE_TYPE wRemoveMsg);
+
+//    [LibraryImport("USER32.dll", SetLastError = true)]
+//    public static partial int GetMessageW(ref WIN_MESSAGE lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax);
+
+//    [LibraryImport("USER32.dll")]
+//    public static partial int TranslateMessage(ref WIN_MESSAGE lpMsg);
+
+//    [LibraryImport("USER32.dll")]
+//    public static partial nint DispatchMessageW(ref WIN_MESSAGE lpMsg);
+//#else
+//    [DllImport("USER32.dll")]
+//    public static extern int PeekMessageW(ref WIN_MESSAGE lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax, PEEK_MESSAGE_REMOVE_TYPE wRemoveMsg);
+
+//    [DllImport("USER32.dll", SetLastError = true)]
+//    public static extern int GetMessageW(ref WIN_MESSAGE lpMsg, IntPtr hWnd, uint wMsgFilterMin, uint wMsgFilterMax);
+
+//    [DllImport("USER32.dll")]
+//    public static extern int TranslateMessage(ref WIN_MESSAGE lpMsg);
+
+//    [DllImport("USER32.dll")]
+//    public static extern nint DispatchMessageW(ref WIN_MESSAGE lpMsg);
+//#endif
   }
 }

src/NTwain/TwainAppSession.Callbacks.cs

@@ -112,24 +112,17 @@ namespace NTwain
           if (!_inTransfer)
           {
             // this should be done on ui thread (or same one that enabled the ds)
-            _uiThreadMarshaller.Post(obj =>
-            {
-              ((TwainAppSession)obj!).DisableSource();
-            }, this);
+            DisableSource();
           }
           break;
         case MSG.DEVICEEVENT:
           if (DeviceEvent != null && DGControl.DeviceEvent.Get(ref _appIdentity, ref _currentDS, out TW_DEVICEEVENT de) == TWRC.SUCCESS)
           {
-            _uiThreadMarshaller.Post(obj =>
+            try
             {
-              try
-              {
-                var twain = (TwainAppSession)obj!;
-                twain.DeviceEvent!.Invoke(twain, de);
-              }
-              catch { }
-            }, this);
+              DeviceEvent.Invoke(this, de);
+            }
+            catch { }
           }
           break;
       }

src/NTwain/TwainAppSession.PropEvents.cs

@@ -57,14 +57,11 @@ namespace NTwain
         if (_state != value)
         {
           _state = value;
-          _uiThreadMarshaller.Send(obj =>
+          try
           {
-            try
-            {
-              ((TwainAppSession)obj!).StateChanged?.Invoke(this, value);
-            }
-            catch { }
-          }, this);
+            StateChanged?.Invoke(this, value);
+          }
+          catch { }
         }
       }
     }

src/NTwain/TwainAppSession.Sources.cs

@@ -105,6 +105,18 @@ namespace NTwain
     /// Otherwise capturing will begin after this.</param>
     /// <returns></returns>
     public STS EnableSource(bool showUI, bool uiOnly)
+    {
+      if (_pumpThreadMarshaller == null) return EnableSourceReal(showUI, uiOnly);
+
+      var sts = default(STS);
+      _pumpThreadMarshaller.Send(_ =>
+      {
+        sts = EnableSourceReal(showUI, uiOnly);
+      }, null);
+      return sts;
+    }
+
+    private STS EnableSourceReal(bool showUI, bool uiOnly)
     {
       if (State > STATE.S4)
       {
@@ -136,6 +148,17 @@ namespace NTwain
     /// </summary>
     /// <returns></returns>
     public STS DisableSource()
+    {
+      if (_pumpThreadMarshaller == null) return DisableSourceReal();
+
+      var sts = default(STS);
+      _pumpThreadMarshaller.Send(_ =>
+      {
+        sts = DisableSourceReal();
+      }, null);
+      return sts;
+    }
+    STS DisableSourceReal()
     {
       _closeDsRequested = true;
       var rc = DGControl.UserInterface.DisableDS(ref _appIdentity, ref _currentDS, ref _userInterface);

src/NTwain/TwainAppSession.Xfers.cs

@@ -67,18 +67,11 @@ namespace NTwain
         do
         {
           var readyArgs = new TransferReadyEventArgs(pending.Count, (TWEJ)pending.EOJ);
-          if (TransferReady != null)
+          try
           {
-            _uiThreadMarshaller.Send(_ =>
-            {
-              try
-              {
-
-                TransferReady.Invoke(this, readyArgs);
-              }
-              catch { } // don't let consumer kill the loop if they have exception
-            }, null);
+            TransferReady?.Invoke(this, readyArgs);
           }
+          catch { } // don't let consumer kill the loop if they have exception
 
           if (readyArgs.Cancel == CancelType.EndNow || _closeDsRequested)
           {
@@ -150,27 +143,21 @@ namespace NTwain
             }
             catch (Exception ex)
             {
-              _uiThreadMarshaller.Send(obj =>
+              try
               {
-                try
-                {
-                  var twain = ((TwainAppSession)obj!);
-                  twain.TransferError?.Invoke(twain, new TransferErrorEventArgs(ex));
-                }
-                catch { }
-              }, this);
+                TransferError?.Invoke(this, new TransferErrorEventArgs(ex));
+              }
+              catch { }
             }
           }
         } while (sts.RC == TWRC.SUCCESS && pending.Count != 0);
       }
 
       HandleXferCode(ref sts, ref pending);
+
       if (State >= STATE.S5)
       {
-        _uiThreadMarshaller.Send(obj =>
-        {
-          ((TwainAppSession)obj!).DisableSource();
-        }, this);
+        DisableSource();
       }
       _inTransfer = false;
     }
@@ -185,11 +172,11 @@ namespace NTwain
           break;
         case TWRC.CANCEL:
           // might eventually have option to cancel this or all like transfer ready
-          _uiThreadMarshaller.Send(obj =>
+          try
           {
-            var twain = ((TwainAppSession)obj!);
-            twain.TransferCanceled?.Invoke(twain, new TransferCanceledEventArgs());
-          }, this);
+            TransferCanceled?.Invoke(this, new TransferCanceledEventArgs());
+          }
+          catch { }
           sts = WrapInSTS(DGControl.PendingXfers.EndXfer(ref _appIdentity, ref _currentDS, ref pending));
           sts = WrapInSTS(DGControl.PendingXfers.Reset(ref _appIdentity, ref _currentDS, ref pending));
           if (sts.RC == TWRC.SUCCESS) State = STATE.S5;

src/NTwain/TwainAppSession.cs

@@ -19,26 +19,24 @@ namespace NTwain
     /// <summary>
     /// Creates TWAIN session with app info derived an executable file.
     /// </summary>
-    /// <param name="uiThreadMarshaller"></param>
     /// <param name="exeFilePath"></param>
     /// <param name="appLanguage"></param>
     /// <param name="appCountry"></param>
-    public TwainAppSession(SynchronizationContext uiThreadMarshaller,
+    public TwainAppSession(
       string exeFilePath,
       TWLG appLanguage = TWLG.ENGLISH_USA, TWCY appCountry = TWCY.USA) :
-      this(uiThreadMarshaller, FileVersionInfo.GetVersionInfo(exeFilePath), appLanguage, appCountry)
+      this(FileVersionInfo.GetVersionInfo(exeFilePath), appLanguage, appCountry)
     { }
     /// <summary>
     /// Creates TWAIN session with app info derived from a <see cref="FileVersionInfo"/> object.
     /// </summary>
-    /// <param name="uiThreadMarshaller"></param>
     /// <param name="appInfo"></param>
     /// <param name="appLanguage"></param>
     /// <param name="appCountry"></param>
-    public TwainAppSession(SynchronizationContext uiThreadMarshaller,
+    public TwainAppSession(
         FileVersionInfo appInfo,
         TWLG appLanguage = TWLG.ENGLISH_USA, TWCY appCountry = TWCY.USA) :
-        this(uiThreadMarshaller,
+        this(
           appInfo.CompanyName ?? "",
           appInfo.ProductName ?? "",
           appInfo.ProductName ?? "",
@@ -48,7 +46,6 @@ namespace NTwain
     /// <summary>
     /// Creates TWAIN session with explicit app info.
     /// </summary>
-    /// <param name="uiThreadMarshaller"></param>
     /// <param name="companyName"></param>
     /// <param name="productFamily"></param>
     /// <param name="productName"></param>
@@ -57,12 +54,15 @@ namespace NTwain
     /// <param name="appLanguage"></param>
     /// <param name="appCountry"></param>
     /// <param name="supportedTypes"></param>
-    public TwainAppSession(SynchronizationContext uiThreadMarshaller,
+    public TwainAppSession(
         string companyName, string productFamily, string productName,
         Version productVersion, string productDescription = "",
         TWLG appLanguage = TWLG.ENGLISH_USA, TWCY appCountry = TWCY.USA,
         DG supportedTypes = DG.IMAGE)
     {
+#if WINDOWS || NETFRAMEWORK
+      DSM.DsmLoader.TryLoadCustomDSM();
+#endif
       // todo: find a better place for this
       if (!__encodingRegistered)
       {
@@ -93,7 +93,6 @@ namespace NTwain
       _legacyCallbackDelegate = LegacyCallbackHandler;
       _osxCallbackDelegate = OSXCallbackHandler;
 
-      _uiThreadMarshaller = uiThreadMarshaller;
       StartTransferThread();
     }
 
@@ -104,7 +103,7 @@ namespace NTwain
 #endif
     // test threads a bit
     //readonly BlockingCollection<MSG> _bgPendingMsgs = new();
-    private readonly SynchronizationContext _uiThreadMarshaller;
+    SynchronizationContext? _pumpThreadMarshaller;
     bool _closeDsRequested;
     bool _inTransfer;
     readonly AutoResetEvent _xferReady = new(false);
@@ -176,13 +175,15 @@ namespace NTwain
     /// Loads and opens the TWAIN data source manager.
     /// </summary>
     /// <param name="hwnd">Required if on Windows.</param>
+    /// <param name="uiThreadMarshaller">Context for TWAIN to invoke certain actions on the thread that the hwnd lives on.</param>
     /// <returns></returns>
-    public STS OpenDSM(IntPtr hwnd)
+    public STS OpenDSM(IntPtr hwnd, SynchronizationContext uiThreadMarshaller)
     {
       var rc = DGControl.Parent.OpenDSM(ref _appIdentity, hwnd);
       if (rc == TWRC.SUCCESS)
       {
         _hwnd = hwnd;
+        _pumpThreadMarshaller = uiThreadMarshaller;
         State = STATE.S3;
         // get default source
         if (DGControl.Identity.GetDefault(ref _appIdentity, out TW_IDENTITY_LEGACY ds) == TWRC.SUCCESS)
@@ -223,6 +224,7 @@ namespace NTwain
         }
         catch { }
         _hwnd = IntPtr.Zero;
+        _pumpThreadMarshaller = null;
       }
       return WrapInSTS(rc, true);
     }