ZXing.Delphi-正确使用TThread.Synchronize吗？

Question

I'm starting a project for barcode reading in a FMX/Android app (new to barcode reading, I've some experience with FMX).

I found this open-source ZXing.Delphi library (greatly helpful) and I went through the code of this example .

I may not be used enough to TThread but I'm wondering on the use of TThread.Synchronize in this case, because I have never seen/used it like this before.

1 - The function responsible for capturing + scanning an image in search of a barcode is GetImage . It is sync'd to main thread on CameraComponent1SampleBufferReady .

procedure TMainForm.CameraComponent1SampleBufferReady(Sender: TObject;
  const ATime: TMediaTime);
begin
  TThread.Synchronize(TThread.CurrentThread, GetImage);
end;

2 - GetImage function contains TTask.Run which again makes use of TThread.Synchronize to sync to the main thread.

procedure TMainForm.GetImage;
var scanBitmap: TBitmap; ReadResult: TReadResult;
begin

  CameraComponent1.SampleBufferToBitmap(imgCamera.Bitmap, True);

...

  scanBitmap := TBitmap.Create();
  scanBitmap.Assign(imgCamera.Bitmap);
  ReadResult := nil;

  // There is bug in Delphi Berlin 10.1 update 2 which causes the TTask and
  // the TThread.Synchronize to cause exceptions.
  // See: https://quality.embarcadero.com/browse/RSP-16377

  TTask.Run(
  procedure
  begin
    try
      FScanInProgress := True;
      try
        ReadResult := FScanManager.Scan(scanBitmap);
      except
        on E: Exception do
        begin
          TThread.Synchronize(nil,
          procedure
          begin
            lblScanStatus.Text := E.Message;
          end);

          exit;
        end;
      end;

      TThread.Synchronize(nil,
      procedure
      begin

        ...

        if (ReadResult <> nil) then
        begin
          Memo1.Lines.Insert(0, ReadResult.Text);
        end;

      end);

    finally
      ReadResult.Free;
      scanBitmap.Free;
      FScanInProgress := false;
    end;

  end);

end;

? : Is it usual/good pratice to encapsulate TThread.Synchronize( TTask.Run( TThread.Synchronize(...) ) ); ?

? : Couldn't it be the cause of the mentionned exceptions encountered in Delphi 10.1 update 2 ?

When I "learned" to use Parallel Programming Library, I mainly used :

• this entry on Emb'ro

• Malcolm Groves' blog

• this CodeRage 9 video

Did I missed it somewhere ?

Answer 1

A quick update. With Embarcadero 10.3.1:

TThread.Synchronize(TThread.CurrentThread, GetImage);

generates after a random number of seconds a Segmentation Fault. You can notice a many "Switch To Thread" calls suring debug and it will always crash the APP. No matter if you leave GetImage function empty. I've tried all the possibile ways but my app and also the original app crashes. I've also tried creating an Asyincronous thread as well as Labda... same results all the times It looks like TThread Synchronization has issues on 10.3.1. Other users reported to have it working fine on previous Tokyo version.

Any feedback from your side?