Option to failFast on zip and sequence

[scabug]

It should be possible to supply a flag to fail fast on both zip and sequence operations.

val a = Future{Thread.sleep(5000);1}
val b = Future{Thread.sleep(1000); throw new Exception("test")}
val c = a zip b

c will fail in 5 seconds with the exception from B.

Most clients would probably prefer it to fail in 1 second even if that means that they might get an exception from Future b instead of a possible exception from Future a.

[scabug]

Imported From: https://issues.scala-lang.org/browse/SI-8994?orig=1
Reporter: @jedesah
Affected Versions: 2.11.4

[scabug]

@jedesah said:
I would be glad to issue the PR if this is deemed useful.

[scabug]

@retronym said (edited on Nov 25, 2014 5:16:30 AM UTC):
@phaller WDYT?

[scabug]

Oscar Boykin (oscar) said:
Implemented such a method here:

https://github.com/twitter/scalding/pull/1412/files

I'll try to make a PR to the scala repo to discuss mainlining this.

[julienrf]

I think this is an important issue. In addition to this, I’ve noticed that zip is not commutative “fail-wise”.

See this snippet:

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.{ Await, Future, blocking }
import scala.concurrent.duration.Duration

def failing() = Future.failed(new Exception("KO"))
def succeeding() = Future(blocking(Thread.sleep(5000)))

System.currentTimeMillis() / 1000 // : Long = 1603205724
Await.ready(failing().zip(succeeding()), Duration.Inf)
System.currentTimeMillis() / 1000 // : Long = 1603205724
Await.ready(succeeding().zip(failing()), Duration.Inf)
System.currentTimeMillis() / 1000 // : Long = 1603205729

Note that executing failing().zip(succeeding()) completes instantaneously, whereas executing succeeding().zip(failing()) completes only after succeeding() completes.

I think we should fix zip such that a.zip(b) fails as soon as a or b fails. We should also make sure that sequence and traverse are fixed.