c++ : updating progress bar from std::async

It is an all time classics problem, but to be honest I haven't found a simple example of how to update a progress bar by an async function call.

lets say I have(not the accurate code, but the main flow is like this):

int main (){

    ProgressBar progressBar = new ProgressBar();


    for (int i = 0; i < cores; i++) {
      std::shared_future f = std::async(std::launch::async, myFunc, 
       myFunctionArgument);
      futures.push_back(f);
    }


    std::vector resCollects;
    for (std::shared_future f : futures)
    {
      MyObj* res = f.get();
      resCollects.push_back(res);
    }
return;
}

The computationally heavy task that has to be carried out async the job per core is here:

    MyObj* myFunc (MyFunctionArgument myFunctionArgument){
     for(int i=0; i < myFunctionArgument.size(); i++){
       doLongCalculations(myFunctionArgument.data);
       //HOW DO I UPDATE THE PROGRESS BAR THAT A SMALL FRAGMENT OF THE TASK HAS BEEN 
       //COMPLETED? updateProgressBar(int i);
     }
    }

The class ProgressBar is in a simple form:

    class ProgressBar{
      private: 
                int totalTasks;
                int currentProgress;
     public:
       void updateProgressBar(int i){
         cout<<" The current progress is: " << i << "out of "<< 
     totalTasks;
        }
    
    }

Supposing I have already implemented a simple class of progress bar which takes an integer and updates the percentage of the total task(of which I know the total size) that has been completed, what's the basic design of updating that progress bar? Where should i call "updateProgressBar(int i) from? I need a very simple example to understand the design of the solution how to emit and receive progress.

Thanks!