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Thread = class(TThread)
private
  fPauseEvent: Cardinal;
public
  property PauseEvent: Cardinal read fPauseEvent;
  procedure Execute; override;
  constructor Create(Suspended: Boolean);
  destructor Destroy; override;
end;

procedure Thread.Execute;
var
  Finished: Boolean;
begin
  Finished := False;
  while not Finished do begin 
    if WaitForSingleObject(fPauseEvent, 0) = WAIT_OBJECT_0 then
      Suspend;
    if Terminated then
      Finished := True;
  end;
end;

constructor TGenTipPlanThread.Create(Suspended: Boolean);
begin
  inherited Create(Suspended);
  fPauseEvent   := CreateEvent(nil, True, False, '');
  ResetEvent(fPauseEvent);
end;

destructor TGenTipPlanThread.Destroy;
begin
  CloseHandle(fPauseEvent);
  inherited Destroy;
end;

//IM MAIN-THREAD///////////////////////////////////////
procedure TForm.SuspendThreadBtClick(Sender: TObject);
begin
  if Assigned(Thread) then
    SetEvent(Thread.PauseEvent);
end;

procedure TForm.ResumeThreadBtClick(Sender: TObject);
begin                                                                               
  if Assigned(Thread) then
    if Thread.Suspended then begin
      ResetEvent(Thread.PauseEvent);
      Thread.Resume;
    end;
end;