Re: Are Errors in a Future body rethrown, as per the documentation?

Andrew,

Indeed, also see revisions to NonFatal.

-- 
Cheers,
√
On 14 Jul 2015 00:17, "Andrew Phillips" <[email protected]> wrote:

> Hi Viktor
>
> > See the revision history / Issues for details.
>
> Thanks for the hint. The last change related to this seems to have
> been SI-7029 ("Fork join execution context loses fatal exceptions") [1],
> which added code to pass any exceptions caught to the fork-join pool
> thread's uncaught exception handler [2]. The above example is not related
> to the fork-join executor, however.
>
> The discussion in the issue has hopefully put me on the right track,
> though: what seems to be the case is that only *fatal* exceptions (as
> determined by NonFatal [3]) are re-thrown...and this includes
> ControlThrowable and InterruptedException, but *not* Error.
>
> Tweaking my original example to use InterruptedException gives the
> desired result:
>
> scala> Future { throw new InterruptedException("bang!") }.value
> DEBUG: running
> scala.concurrent.impl.Future$PromiseCompletingRunnable@7e6ce0a3
> java.lang.InterruptedException: bang!
>   at $anonfun$1.apply(<console>:12)
>   at $anonfun$1.apply(<console>:12)
>   at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.liftedTree1$1(Future
> .scala:24)
>   at
> scala.concurrent.impl.Future$PromiseCompletingRunnable.run(Future.scala:24)
>
>   at SameThreadExecutionContext$.execute(<console>:13)
>   at scala.concurrent.impl.Future$.apply(Future.scala:31)
>   at scala.concurrent.Future$.apply(Future.scala:492)
>   ... 33 elided
>
>
> See https://github.com/scala/scala.github.com/pull/434
>
> Regards
>
> ap
>
> [1] https://issues.scala-lang.org/browse/SI-7029
> [2]
> https://github.com/scala/scala/commit/3f78bee128bd6a478bef6a66c5574f77a2d6dd74
> [3]
> https://github.com/scala/scala/blob/2.11.x/src/library/scala/util/control/NonFatal.scala#L37
>
> On Monday, July 13, 2015 at 5:05:12 PM UTC-4, √iktor Klang wrote:
>>
>> Hi Andrew,
>>
>> I think that behaviour was changed later on.
>> See the revision history / Issues for details.
>>
>> On Mon, Jul 13, 2015 at 10:09 PM, Andrew Phillips <[email protected]>
>> wrote:
>>
>>> Hi all
>>>
>>> With regard to the handling of Errors, the "Futures and Promises"
>>> documentation [1] states:
>>>
>>> ExecutionException - stored when the computation fails due to an
>>>> unhandled InterruptedException, Error or a
>>>> scala.util.control.ControlThrowable. In this case the
>>>> ExecutionException has the unhandled exception as its cause. *These
>>>> exceptions are rethrown in the thread executing the failed asynchronous
>>>> computation.*
>>>
>>>
>>> Is this latter statement true in general, e.g. also if you supply your
>>> own ExecutionContext? Or does it depend on the ExecutionContext
>>> implementation?
>>>
>>> In this example at least, nothing seems to be rethrown (or passed to
>>> reportFailure, for that matter):
>>>
>>> Welcome to Scala version 2.11.6 (Java HotSpot(TM) 64-Bit Server VM, Java
>>> 1.7.0_40).
>>>
>>>
>>> import scala.concurrent.Future
>>> import scala.concurrent.ExecutionContext
>>> import scala.util.{Failure, Success}
>>>
>>>
>>> implicit object SameThreadExecutionContext extends ExecutionContext {
>>>   override def execute(runnable: Runnable): Unit = {
>>>     println("DEBUG: running " + runnable)
>>>     runnable.run()
>>>   }
>>>   override def reportFailure(t: Throwable): Unit = ??? // never called?
>>> }
>>>
>>> scala> Future { throw new Error("bang!") }.value
>>> DEBUG: running
>>> scala.concurrent.impl.Future$PromiseCompletingRunnable@887b5d0
>>> res1: Option[scala.util.Try[Nothing]] =
>>> Some(Failure(java.util.concurrent.ExecutionException: Boxed Error))
>>>
>>>
>>> Am I missing something or misreading the docs here?
>>>
>>> Regards
>>>
>>> ap
>>>
>>> [1] http://docs.scala-lang.org/overviews/core/futures.html#exceptions
>>>
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>>
>>
>>
>> --
>> Cheers,
>> √
>>
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