How do I reference the tbb::task_group_context object inside a parallel_for loop

[tbbuser]

tbb::task_group_context tg;
SomeClass someObject;

tbb:: parallel_for(tbb::blocked_range<size_t>(0, num, grainSize), 
                   someObject,
                   tbb::simple_partitioner(),
                   tg);
I need to reference tg inside the functor definition of SomeClass so that I can cancel 
all the threads under some conditons

lass SomeClass
{
void operator()(const tbb::blocked_range<size_t>& r)  const{
  if (somthing < 0)
    tg.cancel_group_execution();
}

I get compiler error : "tg" not declared in this scope. 
How do i reference the "tg" that is being passed into the parallel_for loop

[Mark_L_Intel · Accepted solution]

Please look at https://oneapi-src.github.io/oneTBB/main/tbb_userguide/Cancellation_Without_An_Exception.html. Does it help? 

[tbbuser]

Thank you for the solution. That works