OpenPictureDialog creates 13 threads but does not destroy all threads upon destruction in Delphi

Question

I am noticing a strange behaviour with TOpenPictureDialog.

When creating and executing a TOpenPictureDialog, 13 threads are created, and when the dialog is destroyed, the threads remain present according to Windows Activity Monitor, except of 1 thread, which disappears.

Why is this happening?

The code I am using is the following:

 var opd: TOpenPictureDialog;
begin
  opd := TOpenPictureDialog.Create(self);
  opd.Execute;
  if opd.FileName = '' then exit;
  opd.Free;
begin;

I am using Delphi XE2 with Windows 8.1

Answer 1

TOpenPictureDialog does not create any threads of its own. They are all internal to the OS Shell, and they are cached and reused by the Shell as needed. You have no control over them, nor should you be worrying about them. Let the Shell do its job.

BTW, your code is not freeing the dialog if it is canceled or fails. Use a try/finally block to avoid that:

var
  opd: TOpenPictureDialog;
begin
  opd := TOpenPictureDialog.Create(nil);
  try
    if not opd.Execute then Exit;
    // use opd.FileName as needed...
  finally
    opd.Free;
  end;
end;