Add `.exceptionally` to pool submission in Vulpix

[felixmulder]

Vulpix submits runnables to a thread pool in ParallelTesting.scala. These submissions generate futures which do not have an exception handler.

By doing .exceptionally we could add handlers for these. This would be useful for not foregoing any stacktraces that might be lost.

[allanrenucci]

.exceptionally is only available on CompletableFuture and not Future. I don't think it is possible to register an exception handler. @felixmulder Did you have something else in mind?

[smarter]

I outlined a possible solution here: https://gitter.im/lampepfl/dotty?at=59c14f031081499f1f4eb663

[felixmulder]

Guillaume's solution sounds a bit hacky TBH :)

What workStealingPool is doing is creating a ForkJoinPool and supplying a specific thread factory. The thread is created with a default exception handler. Should be possible to give the ForkJoinPool a different factory which has a better handler :)

[felixmulder]

But I haven't looked into it further than that...

[allanrenucci]

Indeed, one could do:

val pool = new ForkJoinPool()
val tasks = filteredSources.map(s => pool.submit(...))
// wait for termination
...
val errors = tasks.map(_.getException).filter(_ != null)

or

val futures = filteredSources
  .map(s => CompletableFuture.supplyAsync(..., pool))
  .map(_.exceptionally(...))

[allanrenucci]

Keeping this open as the current solution can be improved

[SzymonPajzert]

How would you like to improve current solution? Is didFail returning true if any exception is called during eventualResults.foreach(_.get)?