ActorTaskScheduler QueueTask for LongRunning

[Zetanova]

Some external Sources are lazy initializing background threads with the LongRunning Task hint.
Like with RX Subject on the first OnNext()
With the current ActorTaskScheduler behavior the actor will lock at Line64 TryExecuteTask(task);
The deault behavir of the TaskPoolScheduler would be to start a detached explicit Thread for this Task.

[Zetanova]

The Cancled Check is missing at line65
if (task.IsFaulted || task.IsCanceled)
Rethrow(task, null);

[Danthar]

Can you confirm this bug with a Test/Spec ?
After which, you are most welcome to do a PR for this :)

[Zetanova]

I created a Spec, but of couse it is failing.

There are multiple possible options for the ActorTaskScheduler

1. It creates only a detetched Thread on TaskCreationOptions.LongRunning
2. It uses the CompleteTask-Message only for a TaskCreationOptions.AttachedToParent

[Aaronontheweb]

@Zetanova so your spec proves definitively that this is an issue.

What's the appropriate fix?

[Danthar]

@Zetanova your right about the check on line 65. That should include the IsCanceled check.

However i'm not sure what you mean with the possible options for the ActorTaskScheduler. As in, how would that solve the problem?

[Zetanova]

Currently the ActorTaskScheduler is executing all task-types with the help of the CompleteTask-Message.
Some Libraries can have hidden side-effects that they are requesting a task internaly
for a long running process.
Like System.Reactive on the first call of OnNext() method.

if currently something is requesting a LongRunning Task, it will probably lock the actor with it.

If something requires a Long Running Task for lets say an infinit message loop
it normaly is requesting the Task with the TaskCreationOptions.LongRunning flag
and correctly assume that it can run this task for a long period.
A separate and new created thread is used for this task by the TaskPoolScheduler.

I didn't thought it through but maybe the ActorTaskScheduler can behave like the normal TaskPoolScheduler for all Task-types beside TaskCreationOptions.AttachedToParent
and only using the CompleteTask-Message on tasks that are attached as childs
with the AttachedToParent flag set.

The ActorTaskScheduler schould allways create a new thread for the a LongRunning -Task
and yes, it is running then outside of the akka context.

[Aaronontheweb]

@Zetanova got it - so this is possibly related to #1346 (see PR #1347) and also the use of TaskCreationOptions.LongRunning. Could you modify your PR to include a change for this on ActorTaskScheduler?

[JeffCyr]

I'm a bit confused by the comments and commits in this issue. ActorTaskScheduler's purpose is to execute a task in the Actor's context, it make sense to spin a thread when the flag LongRunning is set, but it does not make sense to execute a task outside the actor context ever.

See Issue #1481 and PR #1482, I implemented the LongRunning flag.