Threads in VST

[Dzyszla]

I have very hard problem - in some case, when I have window with VST in DLL, and I close it, whole application sometimes crash with AV error in unloaded DLL (especially on slow computers).

If I add sleep (f.ex. 500 ms) after window free, but before end of DLL's procedure (witch open and free my form with VST), then looks work good.

So, I think it can be some mistake in some thread... But where?

I look on VirtualTrees.WorkerThread file and Dispose procedure and have question: why is there terminate and setevent, but not waiting for really terminate thread (WaitFor)? But I'm not sure this applies to my case or this is true mistake.

It's applies to 7.x and 8.0 version.

[joachimmarder]

What exactly make you think that the thread of Virtual TreeView causes the crash?

[Dzyszla]

I attach demo code (two projects: exe and dll):
VST_Test.zip

On my computer have no errors, but when I run it on Windows 2012/2016/2019 Server, click button and close window (by shortcut, by mouse click - no matter) in 1 on 10 times crash (but sometime can be 10 times without error, and next every 3 run and close ends with crash).
here attach system logs:
VSTerrors.zip

[Dzyszla]

PS - When I made changes in dispose method, then works good:

class procedure TWorkerThread.Dispose(CanBlock: Boolean);
var
  LRef: TThread;
begin
  WorkerThread.FreeOnTerminate := False;   // << NEVR USE FREE ON TERMINATE
  //WorkerThread.FreeOnTerminate := not CanBlock;  // << -- " --
  WorkerThread.Terminate();
  SetEvent(WorkerThread.FWorkEvent);
  LRef := WorkerThread;
  WorkerThread.WaitFor; // << ADD WAITING  FOR TERMINATE
  WorkerThread := nil; //Will be freed usinf TThread.FreeOnTerminate
  //if CanBlock then   << DISABLE THIS LINE - OBJECT MUST BE ALWAYS FREE
	LRef.Free;
end;

[joachimmarder]

I didn't get a single crash in 30 tries with your demo project.

Can you please check if the following change makes any difference in your case: In TBaseVirtualTree.Destroy() change the call to TWorkerThread.ReleaseThreadReference to:

TWorkerThread.ReleaseThreadReference(IsLibrary);

[Dzyszla]

I try my demo on my own system, and it's crash after about 1 on 60-80 trials (very infrequently, but possible). I think, it depends on cpu cores load.

I made the changes as suggested (and I rolled back my own previous changes) and looks all right - no more crashes.