events - what is the best way to get notified when a task finishes, in F#?

Question

I have a pool of tasks and I am trying to figure out the best way to be notified, through an event, when one is finished.

Since the tasks are quite varied, I don't want to add a piece of code inside the task itself since that would mean putting it in several places. These are long running tasks, I'm not waiting for them to complete anywhere, they're just getting started, do their work (minutes to days) and then they finish.

The ugly-but-could-work solution is to wrap each work task into another task that awaits for the work task to be complete and then sends an event, but I'm hoping there would be something more elegant.

question from:https://stackoverflow.com/questions/66060890/what-is-the-best-way-to-get-notified-when-a-task-finishes-in-f

Answer 1

In a comment you explained that you're starting your tasks like this:

Async.StartAsTask (runner.Start(), TaskCreationOptions.LongRunning, cancellationSource.Token)

Instead of doing that, start them like this:

startMyTask runner cancellationSource (fun() -> printfn "Task completed!")

Where:

let startMyTask (runner: RunnerType) (s: CancellationTokenSource) onDone = 
    let wrapper = async { 
      do! runner.Start()
      onDone() 
    }
    Async.StartAsTask (wrapper, TaskCreationOptions.LongRunning, s.Token)