How can I get scala's blocking to work with tailrec? - scala

Question

I'm writing scala <-> java interop wrappers for Futures and I don't know the Right Way to implement scala.concurrent.Future.onComplete (http://www.scala-lang.org/api/current/index.html#scala.concurrent.Future). This probably works:
def onComplete[U](func: Try[T] => U)(implicit executor: ExecutionContext): Unit = {
executor.execute(new Runnable {
#tailrec
def run = value match {
case Some(t) => func(t)
case None => { Thread.sleep(100); run }
}
})
}
but Asynchronous IO in Scala with futures suggests that when I have to block I should pass the relevant part of the code to scala.concurrent.blocking to let the ExecutionContext know what's up. The problem is that when I surround the value match{...} with blocking {} it's no longer a tail call.
What's the proverbial right way to do this?
Edit: for completeness here is the entire wrapping class:
class JavaFutureWrapper[T](val jf: java.util.concurrent.Future[T]) extends scala.concurrent.Future[T] {
def isCompleted = jf.isDone
def result(atMost: Duration)(implicit permit: CanAwait): T =
atMost match { case Duration(timeout, units) => jf.get(timeout, units) }
def onComplete[U](func: Try[T] => U)(implicit executor: ExecutionContext): Unit = {
executor.execute(new Runnable {
#tailrec
def run = value match {
case Some(t) => func(t)
case None => { Thread.sleep(100); run }
}
})
}
def ready(atMost: Duration)(implicit permit: CanAwait): this.type = atMost match {
case Duration(timeout, units) => {
jf.get(timeout, units)
this
}
}
def value: Option[Try[T]] = (jf.isCancelled, jf.isDone) match {
case (true, _) => Some(Failure(new Exception("Execution was cancelled!")))
case (_, true) => Some(Success(jf.get))
case _ => None
}
}

Answer 1

I would just wait for the Java future to complete:
import scala.util.{Try, Success, Failure}
import scala.concurrent._
import java.util.concurrent.TimeUnit
class JavaFutureWrapper[T](val jf: java.util.concurrent.Future[T])
extends scala.concurrent.Future[T] {
...
def onComplete[U](func: Try[T] => U)(implicit executor: ExecutionContext): Unit =
executor.execute(new Runnable {
def run: Unit = {
val result = Try(blocking(jf.get(Long.MaxValue, TimeUnit.MILLISECONDS)))
func(result)
}
})
...
}

Answer 2

Hmm, my edit to 0__ 's answer didn't get approved, so for the sake of future readers, here's the solution I'm going with (which is simplified from 0__'s)
def onComplete[U](func: Try[T] => U)(implicit executor: ExecutionContext): Unit = {
executor.execute(new Runnable {
def run = func(Try( blocking { jf.get } ))
})
}