How to know how many tasks are already completed? - delphi

Question

In C++ Builder 10.3.3 I'm using the following test code:
int count = 500;
_di_ITask* task = new _di_ITask[count];
ProgressBar1->Position = 0;
for(int i = 0; i < count; i++){
task[i] = TTask::Create([i, this](){
// do something...
Sleep(10);
});
task[i]->Start();
//ProgressBar1->Position = numberOfFinishedTasks;
//Application->ProcessMessages();
}
TTask::WaitForAll(task, count - 1);
In this case there are 500 test tasks and I would like my ProgressBar component to show the current number of completed tasks. I don't know how to get that info. Thanks!

Answer 1

The simplest solution is to have the lambda itself update the ProgressBar before exiting. You can use TThread::Synchronize() or TThread::Queue() for that.
The problem is, TTask::WaitForAll() is a blocking method that does not pump the main UI message queue at all, so Synchronize()/Queue() requests will not be processed at all. You can get around that by calling WaitForAll() in a loop with a timeout so that the loop can pump messages as needed.
Try something like this:
int count = 500;
std::vector<_di_ITask> task(count);
ProgressBar1->Position = 0;
ProgressBar1->Min = 0;
ProgressBar1->Max = count;
ProgressBar1->Step = 1;
for(int i = 0; i < count; ++i){
task[i] = TTask::Create(
[i, this](){
// do something...
TThread::Queue(nullptr, ProgressBar1->StepIt);
}
);
task[i]->Start();
}
while (!TTask::WaitForAll(task.data(), count - 1, 1000)){
Application->ProcessMessages();
}