Msg loop filter tweaks.

src/NTwain/NTwain.csproj

@@ -31,8 +31,4 @@
       <LastGenOutput>DSMGenerator.dummy</LastGenOutput>
     </None>
   </ItemGroup>
-
-  <ItemGroup>
-    <Service Include="{508349b6-6b84-4df5-91f0-309beebad82d}" />
-  </ItemGroup>
 </Project>

src/NTwain/TwainSession.Sources.cs

@@ -88,20 +88,24 @@ namespace NTwain
     /// <returns></returns>
     public STS EnableSource(bool showUI, bool uiOnly)
     {
-      var ui = new TW_USERINTERFACE
+      if (State != STATE.S4) return STS.SEQERROR; // shouldn't check it ourselves but whatev
+
+      _userInterface = new TW_USERINTERFACE
       {
         ShowUI = (ushort)((showUI || uiOnly) ? 1 : 0),
         hParent = _hwnd,
       };
       var rc = uiOnly ?
-        DGControl.UserInterface.EnableDSUIOnly(ref _appIdentity, ref _currentDS, ref ui) :
+        DGControl.UserInterface.EnableDSUIOnly(ref _appIdentity, ref _currentDS, ref _userInterface) :
-        DGControl.UserInterface.EnableDS(ref _appIdentity, ref _currentDS, ref ui);
+        DGControl.UserInterface.EnableDS(ref _appIdentity, ref _currentDS, ref _userInterface);
       if (rc == STS.SUCCESS || (!uiOnly && !showUI && rc == STS.CHECKSTATUS))
       {
-        // keep it around for disable use
-        _userInterface = ui;
         State = STATE.S5;
-      };
+      }
+      else
+      {
+        _userInterface = default;
+      }
       return rc;
     }
 

src/NTwain/TwainSession.Windows.cs

@@ -17,7 +17,7 @@ namespace NTwain
 
   partial class TwainSession : IMessageFilter
   {
-    private HwndSource? _wpfhook;
+    HwndSource? _wpfhook;
 
     /// <summary>
     /// Registers this session for use in a Winform UI thread.
@@ -75,32 +75,24 @@ namespace NTwain
       bool handled = false;
       if (_state >= STATE.S5)
       {
-        TW_EVENT evt = default;
+        var winMsg = new WIN_MESSAGE
-        try
         {
-          var winMsg = new WIN_MESSAGE
+          hwnd = hWnd,
-          {
+          message = (uint)msg,
-            hwnd = hWnd,
+          wParam = wParam,
-            message = (uint)msg,
+          lParam = lParam
-            wParam = wParam,
+        };
-            lParam = lParam
+        // no need to do another lock call when using marshal alloc
-          };
+        if (_procEvent.pEvent == IntPtr.Zero)
-          // no need to do another lock call when using marshal alloc
+          _procEvent.pEvent = Marshal.AllocHGlobal(Marshal.SizeOf(winMsg));
-          evt.pEvent = Marshal.AllocHGlobal(Marshal.SizeOf(winMsg));
+        Marshal.StructureToPtr(winMsg, _procEvent.pEvent, true);
-          Marshal.StructureToPtr(winMsg, evt.pEvent, false);
 
-          var rc = DGControl.Event.ProcessEvent(ref _appIdentity, ref _currentDS, ref evt);
+        var rc = DGControl.Event.ProcessEvent(ref _appIdentity, ref _currentDS, ref _procEvent);
-          handled = rc == STS.DSEVENT;
+        handled = rc == STS.DSEVENT;
-          if (evt.TWMessage != 0 && (handled || rc == STS.NOTDSEVENT))
+        if (_procEvent.TWMessage != 0 && (handled || rc == STS.NOTDSEVENT))
-          {
-            Debug.WriteLine("Thread {0}: CheckIfTwainMessage at state {1} with MSG={2}.", Thread.CurrentThread.ManagedThreadId, State, (MSG)evt.TWMessage);
-            HandleSourceMsg((MSG)evt.TWMessage);
-          }
-        }
-        finally
         {
-          // do we need to free it
+          Debug.WriteLine("Thread {0}: CheckIfTwainMessage at state {1} with MSG={2}.", Thread.CurrentThread.ManagedThreadId, State, (MSG)_procEvent.TWMessage);
-          if (evt.pEvent != IntPtr.Zero) Marshal.FreeHGlobal(evt.pEvent);
+          HandleSourceMsg((MSG)_procEvent.TWMessage);
         }
       }
       return handled;

src/NTwain/TwainSession.cs

@@ -3,6 +3,7 @@ using NTwain.Triplets;
 using System;
 using System.Collections.Concurrent;
 using System.Diagnostics;
+using System.Runtime.InteropServices;
 using System.Text;
 using System.Threading;
 
@@ -96,8 +97,9 @@ namespace NTwain
     }
 
     internal IntPtr _hwnd;
-    internal TW_USERINTERFACE _userInterface;
+    internal TW_USERINTERFACE _userInterface; // kept around for disable use
-    // test this a bit
+    TW_EVENT _procEvent = default; // kept here so the alloc/free only happens once
+    // test threads a bit
     readonly BlockingCollection<MSG> _bgPendingMsgs = new();
     private readonly IThreadMarshaller _uiThreadMarshaller;
     private bool disposedValue;
@@ -152,6 +154,7 @@ namespace NTwain
           // this will end the bg thread
           _bgPendingMsgs.CompleteAdding();
         }
+        if (_procEvent.pEvent != IntPtr.Zero) Marshal.FreeHGlobal(_procEvent.pEvent);
         disposedValue = true;
       }
     }
@@ -263,10 +266,14 @@ namespace NTwain
       int tries = 0;
       while (State > targetState)
       {
-        if (tries++ > 5) break;
+        var oldState = State;
 
-        switch (State)
+        switch (oldState)
         {
+          // todo: finish
+          case STATE.S7:
+          case STATE.S6:
+            break;
           case STATE.S5:
             DisableSource();
             break;
@@ -277,6 +284,11 @@ namespace NTwain
             CloseDSM();
             break;
         }
+        if (oldState == State)
+        {
+          // didn't work
+          if (tries++ > 5) break;
+        }
       }
       return State;
     }