Interrupting a long calculation


I have a gui that uses

TSpectrum3 s = new TSpectrum3();
s->SearchFast((const float
**) source, dest, Nbins, Nbins, Nbins, Sigma, Threshold, kFALSE, Window);

Because the “search peak” function can take quite a long time, it is run in a separate thread so that the gui is not blocked. I would like to add a “Cancel” button to stop the calculations if the user wants to.
I tried TTread::Kill() and TThread::Delete(), but this does not seem to work (and to be recommended).

I was wondering if Root provides such a functionality that would allow to stop a calculation without
having to write a separate program using pipes, forks and so on (which seems to be the only way I can
figure out at moment)?

Thank You in advance,

Bertrand Roessli

Hi Bertrand,

Take a look at the very simple macro in attachment, it works for me…

Cheers, Bertrand.
Interrupt_Thread.C (1.95 KB)


Thanks for the macro.
Interestingly I cannot stop the macro when clicking on STOP… The only way is to close
the terminal.

I have Root 5.31/1

Bertrand Roessli

Yes, I see, it works only on Windows. :-k I’ll check.
In the meanwhile, if you want to test the macro, you can still add these two lines: if (th1 && th1->GetState() == TThread::kCancelingState) break; inside the while() loop.

Cheers, Bertrand.

Yes, adding

  if (th1 && th1->GetState() == TThread::kCancelingState)

in the while loop works.


Bertrand Roessli


As complement of information: Adding TThread::SetCancelOn(); in the user function solves the problem. For our example:[code]void *JobThread(void *)
// this is the thread function actually doing the real job,
// allowing the main thread to process events

int i = 0;
TThread::SetCancelOn(); // to allow to terminate (kill) the thread
while (1) {
TThread::Sleep(0, 50000000);
printf("%c\r", symb[i]);
if (!symb[++i]) i = 0;
return 0;
Thanks to Philippe who noticed that the TThread::SetCancelOn(); has to be placed inside the user function (the function called by the thread), and that it was not enabled by default…

Cheers, Bertrand.


Yes it works now.

Thanks a lot,

Bertrand Roessli

PS: p 382 of the manual explains that :blush: