How to safely cancel a task using a CancellationToken and await Task.WhenAll

Question

I have a framework which creates a CancellationTokenSource, configures CancelAfter, then calls an async method and passes the Token. The async method then spawns many tasks, pas

Answer 1

I recommend that you follow the standard cancellation pattern of throwing an exception rather than just returning:

public static void DoWork(work, cancellationToken)
{
  while (work.IsWorking)
  {
    cancellationToken.ThrowIfCancellationRequested();
    work.DoNextWork();
  }
}

If you have cleanup work to do, that's what finally is for (or using, if you can refactor that way):

public async Task Run(CancellationToken cancellationToken)
{
  HashSet tasks = new HashSet();
  foreach (var work in this.GetWorkNotPictured)
  {
    tasks.Add(Task.Run(() => this.DoWork(work, cancellationToken))
  }

  try
  {
    await Task.WhenAll(tasks);
  }
  finally
  {
    this.CleanUpAfterWork();
  }
}