Added possibility to handle transferred data by app in another thread for high-speed scanner use.

samples/WinForm32/Form1.Designer.cs

@@ -41,6 +41,7 @@
       lblState = new System.Windows.Forms.Label();
       label3 = new System.Windows.Forms.Label();
       btnOpenDef = new System.Windows.Forms.Button();
+      ckShowUI = new System.Windows.Forms.CheckBox();
       capListView = new System.Windows.Forms.ListView();
       colCap = new System.Windows.Forms.ColumnHeader();
       colType = new System.Windows.Forms.ColumnHeader();
@@ -52,7 +53,7 @@
       btnStart = new System.Windows.Forms.Button();
       btnShowSettings = new System.Windows.Forms.Button();
       btnClose = new System.Windows.Forms.Button();
-      ckShowUI = new System.Windows.Forms.CheckBox();
+      ckBgImageHandling = new System.Windows.Forms.CheckBox();
       ((System.ComponentModel.ISupportInitialize)splitContainer1).BeginInit();
       splitContainer1.Panel1.SuspendLayout();
       splitContainer1.Panel2.SuspendLayout();
@@ -167,6 +168,7 @@
       // 
       // splitContainer1.Panel2
       // 
+      splitContainer1.Panel2.Controls.Add(ckBgImageHandling);
       splitContainer1.Panel2.Controls.Add(ckShowUI);
       splitContainer1.Panel2.Controls.Add(capListView);
       splitContainer1.Panel2.Controls.Add(label4);
@@ -207,6 +209,18 @@
       btnOpenDef.UseVisualStyleBackColor = true;
       btnOpenDef.Click += btnOpenDef_Click;
       // 
+      // ckShowUI
+      // 
+      ckShowUI.AutoSize = true;
+      ckShowUI.Checked = true;
+      ckShowUI.CheckState = System.Windows.Forms.CheckState.Checked;
+      ckShowUI.Location = new System.Drawing.Point(437, 35);
+      ckShowUI.Name = "ckShowUI";
+      ckShowUI.Size = new System.Drawing.Size(69, 19);
+      ckShowUI.TabIndex = 9;
+      ckShowUI.Text = "Show UI";
+      ckShowUI.UseVisualStyleBackColor = true;
+      // 
       // capListView
       // 
       capListView.Anchor = System.Windows.Forms.AnchorStyles.Top | System.Windows.Forms.AnchorStyles.Bottom | System.Windows.Forms.AnchorStyles.Left | System.Windows.Forms.AnchorStyles.Right;
@@ -289,17 +303,17 @@
       btnClose.UseVisualStyleBackColor = true;
       btnClose.Click += btnClose_Click;
       // 
-      // ckShowUI
+      // ckBgImageHandling
       // 
-      ckShowUI.AutoSize = true;
+      ckBgImageHandling.AutoSize = true;
-      ckShowUI.Checked = true;
+      ckBgImageHandling.Checked = true;
-      ckShowUI.CheckState = System.Windows.Forms.CheckState.Checked;
+      ckBgImageHandling.CheckState = System.Windows.Forms.CheckState.Checked;
-      ckShowUI.Location = new System.Drawing.Point(437, 35);
+      ckBgImageHandling.Location = new System.Drawing.Point(512, 35);
-      ckShowUI.Name = "ckShowUI";
+      ckBgImageHandling.Name = "ckBgImageHandling";
-      ckShowUI.Size = new System.Drawing.Size(69, 19);
+      ckBgImageHandling.Size = new System.Drawing.Size(220, 19);
-      ckShowUI.TabIndex = 9;
+      ckBgImageHandling.TabIndex = 10;
-      ckShowUI.Text = "Show UI";
+      ckBgImageHandling.Text = "Handle image data in another thread";
-      ckShowUI.UseVisualStyleBackColor = true;
+      ckBgImageHandling.UseVisualStyleBackColor = true;
       // 
       // Form1
       // 
@@ -345,5 +359,6 @@
     private System.Windows.Forms.ColumnHeader colSupport;
     private System.Windows.Forms.ColumnHeader colExtended;
     private System.Windows.Forms.CheckBox ckShowUI;
+    private System.Windows.Forms.CheckBox ckBgImageHandling;
   }
 }

samples/WinForm32/Form1.cs

@@ -6,12 +6,11 @@ using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Drawing;
-using System.Drawing.Imaging;
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Runtime.Versioning;
 using System.Threading;
+using System.Threading.Tasks;
 using System.Windows.Forms;
 
 namespace WinFormSample
@@ -20,6 +19,8 @@ namespace WinFormSample
   {
     private TwainAppSession twain;
     private readonly string saveFolder;
+    readonly Stopwatch watch = new();
+    private bool _useThreadForImag;
 
     public Form1()
     {
@@ -33,8 +34,9 @@ namespace WinFormSample
       twain.StateChanged += Twain_StateChanged;
       twain.DefaultSourceChanged += Twain_DefaultSourceChanged;
       twain.CurrentSourceChanged += Twain_CurrentSourceChanged;
+      twain.SourceDisabled += Twain_SourceDisabled;
       twain.TransferReady += Twain_TransferReady;
-      twain.Transferred += Twain_DataTransferred;
+      twain.Transferred += Twain_Transferred;
       twain.TransferError += Twain_TransferError;
       twain.DeviceEvent += Twain_DeviceEvent;
 
@@ -47,6 +49,15 @@ namespace WinFormSample
       this.Disposed += Form1_Disposed;
     }
 
+    private void Twain_SourceDisabled(TwainAppSession sender, TW_IDENTITY_LEGACY e)
+    {
+      if (watch.IsRunning)
+      {
+        watch.Stop();
+        MessageBox.Show($"Took {watch.Elapsed} to finish that transfer.");
+      }
+    }
+
     private void SystemEvents_SessionSwitch(object sender, SessionSwitchEventArgs e)
     {
       switch (e.Reason)
@@ -103,28 +114,54 @@ namespace WinFormSample
 
     }
 
-    private void Twain_DataTransferred(TwainAppSession sender, TransferredEventArgs e)
+    private void Twain_Transferred(TwainAppSession sender, TransferredEventArgs e)
     {
       Debug.WriteLine($"[thread {Environment.CurrentManagedThreadId}] data transferred with info {e.ImageInfo}");
-      if (e.Data == null) return;
+      // if using a high-speed scanner, imaging handling could be a bottleneck
+      // so it's possible to pass the data to another thread while the scanning
+      // loop happens. Just remember to dispose it after.
 
-      // example of using some lib to handle image data
+      if (_useThreadForImag)
-      var saveFile = Path.Combine(saveFolder, (DateTime.Now.Ticks / 1000).ToString());
-      using (var img = new ImageMagick.MagickImage(e.Data))
       {
-        if (img.ColorType == ImageMagick.ColorType.Palette)
+        // bad thread example but whatev. should use a dedicated thread of some sort for real
+        Task.Run(() =>
         {
-          // bw or gray
+          HandleTransferredData(e);
-          saveFile += ".png";
+        });
-        }
+      }
-        else
+      else
+      {
+        HandleTransferredData(e);
+      }
+    }
+
+    private void HandleTransferredData(TransferredEventArgs e)
+    {
+      try
+      {
+        // example of using some lib to handle image data
+        var saveFile = Path.Combine(saveFolder, (DateTime.Now.Ticks / 1000).ToString());
+        using (var img = new ImageMagick.MagickImage(e.Data))
         {
-          // color
+          if (img.ColorType == ImageMagick.ColorType.Palette)
-          saveFile += ".jpg";
+          {
-          img.Quality = 75;
+            // bw or gray
+            saveFile += ".png";
+          }
+          else
+          {
+            // color
+            saveFile += ".jpg";
+            img.Quality = 75;
+          }
+          img.Write(saveFile);
+          Debug.WriteLine($"Saved image to {saveFile}");
         }
-        img.Write(saveFile);
+      }
-        Debug.WriteLine($"Saved image to {saveFile}");
+      catch { }
+      finally
+      {
+        e.Dispose();
       }
     }
 
@@ -362,7 +399,11 @@ namespace WinFormSample
 
     private void btnStart_Click(object sender, EventArgs e)
     {
-      twain.EnableSource(ckShowUI.Checked, false);
+      if (twain.EnableSource(ckShowUI.Checked, false).IsSuccess)
+      {
+        _useThreadForImag = ckBgImageHandling.Checked;
+        watch.Restart();
+      }
     }
   }
 }

src/NTwain/Data/BufferedData.cs

@@ -1,22 +1,45 @@
 using System;
+using System.Buffers;
 
 namespace NTwain.Data
 {
   /// <summary>
-  /// Simple struct with bytes buffer and the valid data length.
+  /// Simple thing with shared bytes buffer and the valid data length.
   /// </summary>
-  public struct BufferedData
+  public class BufferedData : IDisposable
   {
+    // experiment using array pool for things transferred in memory.
+    // this can pool up to a "normal" max of legal size paper in 24 bit at 300 dpi (~31MB)
+    // so the array max is made with 32 MB. Typical usage should be a lot less.
+    internal static readonly ArrayPool<byte> MemPool = ArrayPool<byte>.Create(32 * 1024 * 1024, 8);
+
+    public BufferedData(int size)
+    {
+      _buffer = MemPool.Rent(size);
+      _length = size;
+      _fromPool = true;
+    }
+
+    internal BufferedData(byte[] data, int size, bool fromPool)
+    {
+      _buffer = data;
+      _length = size;
+      _fromPool = fromPool;
+    }
+
+    bool _fromPool;
+
     /// <summary>
     /// Bytes buffer. This may be bigger than the data size
     /// and contain invalid data.
     /// </summary>
-    public byte[]? Buffer;
+    byte[]? _buffer;
+    public byte[]? Buffer { get; }
 
     /// <summary>
     /// Actual usable data length in the buffer.
     /// </summary>
-    public int Length;
+    int _length;
 
     /// <summary>
     /// As a span of usable data.
@@ -24,8 +47,17 @@ namespace NTwain.Data
     /// <returns></returns>
     public ReadOnlySpan<byte> AsSpan()
     {
-      if (Buffer != null) return Buffer.AsSpan(0, Length);
+      if (_buffer != null) return _buffer.AsSpan(0, _length);
       return Span<byte>.Empty;
     }
+
+    public void Dispose()
+    {
+      if (_fromPool && _buffer != null)
+      {
+        MemPool.Return(_buffer);
+        _buffer = null;
+      }
+    }
   }
 }

src/NTwain/Native/ImageTools.cs

@@ -24,7 +24,7 @@ namespace NTwain.Native
       return test == 0x4949;
     }
 
-    public static unsafe BufferedData GetBitmapData(System.Buffers.ArrayPool<byte> xferMemPool, IntPtr data)
+    public static unsafe BufferedData? GetBitmapData(IntPtr data)
     {
       var infoHeader = Marshal.PtrToStructure<BITMAPINFOHEADER>(data);
       if (infoHeader.Validate())
@@ -40,7 +40,7 @@ namespace NTwain.Native
         };
         fileHeader.bfSize = fileHeader.bfOffBits + infoHeader.biSizeImage;
 
-        var dataCopy = xferMemPool.Rent((int)fileHeader.bfSize); // new byte[fileHeader.bfSize];
+        var dataCopy = BufferedData.MemPool.Rent((int)fileHeader.bfSize); // new byte[fileHeader.bfSize];
 
         // TODO: run benchmark on which one is faster
 
@@ -58,12 +58,12 @@ namespace NTwain.Native
 
         // write image
         Marshal.Copy(data, dataCopy, fileHeaderSize, (int)fileHeader.bfSize - fileHeaderSize);
-        return new BufferedData { Buffer = dataCopy, Length = (int)fileHeader.bfSize };
+        return new BufferedData(dataCopy, (int)fileHeader.bfSize, true);
       }
       return default;
     }
 
-    public static BufferedData GetTiffData(System.Buffers.ArrayPool<byte> xferMemPool, IntPtr data)
+    public static BufferedData? GetTiffData(IntPtr data)
     {
       // Find the size of the image so we can turn it into a memory stream...
       var headerSize = Marshal.SizeOf(typeof(TIFFHEADER));
@@ -86,10 +86,9 @@ namespace NTwain.Native
 
       if (tiffSize > 0)
       {
-        var dataCopy = xferMemPool.Rent(tiffSize);// new byte[tiffSize];
+        var dataCopy = BufferedData.MemPool.Rent(tiffSize);// new byte[tiffSize];
-        // is this optimal?
         Marshal.Copy(data, dataCopy, 0, tiffSize);
-        return new BufferedData { Buffer = dataCopy, Length = tiffSize };
+        return new BufferedData(dataCopy, tiffSize, true);
       }
       return default;
     }

src/NTwain/TransferReadyEventArgs.cs

@@ -15,13 +15,6 @@ namespace NTwain
       EndOfJobFlag = endOfJobFlag;
     }
 
-
-    /// <summary>
-    /// Gets or sets whether the current transfer should be skipped
-    /// and continue next transfer if there are more data.
-    /// </summary>
-    public bool SkipCurrent { get; set; }
-
     /// <summary>
     /// Gets or sets whether to cancel the capture phase.
     /// </summary>

src/NTwain/TransferredEventArgs.cs

@@ -3,10 +3,8 @@ using System;
 
 namespace NTwain
 {
-  // TODO: maybe a 2-level "dispose" with end of event being 1
-  // and manual dispose 2 for perf if this is not good enough.
 
-  public class TransferredEventArgs : EventArgs
+  public class TransferredEventArgs : EventArgs, IDisposable
   {
     public TransferredEventArgs(TW_AUDIOINFO info, TW_SETUPFILEXFER fileInfo)
     {
@@ -19,7 +17,7 @@ namespace NTwain
       _data = data;
     }
 
-    public TransferredEventArgs(TwainAppSession twain, TW_IMAGEINFO info, TW_SETUPFILEXFER? fileInfo, BufferedData data)
+    public TransferredEventArgs(TwainAppSession twain, TW_IMAGEINFO info, TW_SETUPFILEXFER? fileInfo, BufferedData? data)
     {
       ImageInfo = info;
       FileInfo = fileInfo;
@@ -35,13 +33,13 @@ namespace NTwain
     /// </summary>
     public bool IsImage { get; }
 
-    private readonly BufferedData _data;
+    private readonly BufferedData? _data;
     /// <summary>
     /// The complete file data if memory was involved in the transfer. 
-    /// IMPORTANT: Content of this array may not valid once
+    /// IMPORTANT: Content of this array will not be valid once
-    /// the event handler ends.
+    /// this event arg has been disposed.
     /// </summary>
-    public ReadOnlySpan<byte> Data => _data.AsSpan();
+    public ReadOnlySpan<byte> Data => _data == null ? ReadOnlySpan<byte>.Empty : _data.AsSpan();
 
     /// <summary>
     /// The file info if the transfer involved file information.
@@ -73,5 +71,9 @@ namespace NTwain
       return _twain.GetExtendedImageInfo(ref container);
     }
 
+    public void Dispose()
+    {
+      _data?.Dispose();
+    }
   }
 }

src/NTwain/TwainAppSession.Xfers.cs

@@ -12,11 +12,6 @@ namespace NTwain
 
   partial class TwainAppSession
   {
-    // experiment using array pool for things transferred in memory.
-    // this can pool up to a "normal" max of legal size paper in 24 bit at 300 dpi (~31MB)
-    // so the array max is made with 32 MB. Typical usage should be a lot less.
-    static readonly ArrayPool<byte> XferMemPool = ArrayPool<byte>.Create(32 * 1024 * 1024, 8);
-
     /// <summary>
     /// Can only be called in state 7, so it's hidden here and 
     /// only exposed in data transferred event.
@@ -265,11 +260,11 @@ namespace NTwain
         {
           State = STATE.S7;
           lockedPtr = Lock(dataPtr);
-          BufferedData data = default;
+          BufferedData? data = default;
 
           // TODO: don't know how to read wav/aiff from pointer yet
 
-          if (data.Buffer != null)
+          if (data != null)
           {
             try
             {
@@ -277,10 +272,9 @@ namespace NTwain
               var args = new TransferredEventArgs(info, data);
               Transferred?.Invoke(this, args);
             }
-            catch { }
+            catch
-            finally
             {
-              XferMemPool.Return(data.Buffer);
+              data.Dispose();
             }
           }
         }
@@ -321,7 +315,7 @@ namespace NTwain
       };
       memXferOSX.Memory = memXfer.Memory;
 
-      byte[] dotnetBuff = XferMemPool.Rent((int)buffSize);
+      byte[] dotnetBuff = BufferedData.MemPool.Rent((int)buffSize);
       try
       {
         do
@@ -354,7 +348,7 @@ namespace NTwain
       finally
       {
         if (memPtr != IntPtr.Zero) Free(memPtr);
-        XferMemPool.Return(dotnetBuff);
+        BufferedData.MemPool.Return(dotnetBuff);
       }
 
 
@@ -400,7 +394,7 @@ namespace NTwain
 
       // TODO: how to get actual file size before hand? Is it imagelayout?
       // otherwise will just write to stream with lots of copies
-      byte[] dotnetBuff = XferMemPool.Rent((int)buffSize);
+      byte[] dotnetBuff = BufferedData.MemPool.Rent((int)buffSize);
       using var outStream = new MemoryStream();
       try
       {
@@ -431,7 +425,7 @@ namespace NTwain
       finally
       {
         if (memPtr != IntPtr.Zero) Free(memPtr);
-        XferMemPool.Return(dotnetBuff);
+        BufferedData.MemPool.Return(dotnetBuff);
       }
 
       if (rc == TWRC.XFERDONE)
@@ -440,7 +434,7 @@ namespace NTwain
         {
           DGImage.ImageInfo.Get(ref _appIdentity, ref _currentDS, out TW_IMAGEINFO info);
           // ToArray bypasses the XferMemPool but I guess this will have to do for now
-          var args = new TransferredEventArgs(this, info, fileSetup, new BufferedData { Buffer = outStream.ToArray(), Length = (int)outStream.Length });
+          var args = new TransferredEventArgs(this, info, fileSetup, new BufferedData(outStream.ToArray(), (int)outStream.Length, false));
           Transferred?.Invoke(this, args);
         }
         catch { }
@@ -494,15 +488,15 @@ namespace NTwain
         {
           State = STATE.S7;
           lockedPtr = Lock(dataPtr);
-          BufferedData data = default;
+          BufferedData? data = default;
 
           if (ImageTools.IsDib(lockedPtr))
           {
-            data = ImageTools.GetBitmapData(XferMemPool, lockedPtr);
+            data = ImageTools.GetBitmapData(lockedPtr);
           }
           else if (ImageTools.IsTiff(lockedPtr))
           {
-            data = ImageTools.GetTiffData(XferMemPool, lockedPtr);
+            data = ImageTools.GetTiffData(lockedPtr);
           }
           else
           {
@@ -510,7 +504,7 @@ namespace NTwain
             // don't support more formats :(
           }
 
-          if (data.Buffer != null)
+          if (data != null)
           {
             try
             {
@@ -519,10 +513,9 @@ namespace NTwain
               var args = new TransferredEventArgs(this, info, null, data);
               Transferred?.Invoke(this, args);
             }
-            catch { }
+            catch
-            finally
             {
-              XferMemPool.Return(data.Buffer);
+              data.Dispose();
             }
           }