Thread Problem with GetListOfSpecials()?

Hello Rooters,

I’m having a problem with a null pointer being returned when I try to retrieve the contours from a TH2D.

I have attached a sample script which illustrates my problem, but here is a brief excerpt of the sequence that is causing me trouble (assume TH2D* HistStreamFn is defined):

    HistStreamFn->Draw("CONT LIST");
    // Get Contours
    TObjArray *conts =             (TObjArray*)gROOT->GetListOfSpecials()->FindObject("contours");
    if (conts == NULL){
    	printf("***No Contours Were Extracted!\n");
    	TotalConts = 0;
    	TotalConts = conts->GetSize();

On the first run, conts is null, but repeating the GetListOfSpecials command in the interpreter returns a valid and correct pointer to the contours. This also occurs when running the script a 2nd time.

I suspect this is the result of a multithreading issue since I can successfully retrieve the TObjArray pointer on repeated attempts, but it could also be something I’m doing wrong.

If anyone can shed some light on this I would really appreciate it!

Josh de Bever
CSI Medical Physics Group
The University of Western Ontario
London, Ontario, Canada

System: Mac OSX, ROOT v4.00/04, Single Processor
ROOTtest2.C (2.93 KB)

Hi Josh,

After the line

HistStreamFn->Draw("CONT LIST");

add the line

The contours are only computed when the 2-d histogram is effectlively paint.
or the Users Guide.


Now wasn’t that easy!

I had tried forcing an update on the pad, I don’t know why I didn’t try the canvas.

Many thanks!