Some Random Dude

Updating the UI from a Task

While we’re talking things Parallel, the other part of the same demo from last post showed spawning a single task that slept for awhile and then called ShowMessage.

procedure TFormThreading.Button1Click(Sender: TObject);
var
  aTask: ITask;
  begin
    // not a thread safe snippet
    aTask := TTask.Create(procedure
                          begin
                            sleep(3000); 
                            ShowMessage('Hello');
                          end);
    aTask.Start;
 end;

Note the comment. Read On…

“But what happens if…” : The Joy of Race Conditions

In my last post, I was trying to highlight the fact that just because you have done a WaitForAny and one of your Tasks has ended, the others don’t just all magically stop somehow. It’s good form for your Task to be checking if it has been Cancelled, and to quit as soon as possible, certainly before making any changes outside the context of the Task.

However, as I mentioned at the end of that post, we’re still not done. There is a window of time, albeit a small one, where things could go wrong, and in this post I want to explore what the problem is and how to resolve it. Read On…

WTF is a Future?

Of the abstractions introduced in the Parallel Programming Library, the IFuture<T> seems to be the one that many people have difficulty understanding.

Both TTask and TParallel.For seem reasonably easy to understand conceptually, even if you don’t understand all the details. TTask is about some code you want to run in parallel to the main thread. TParallel.For is about performing some actions on the items in a collection in parallel. In both cases you are focussed on the actions you want to perform. Read On…