`flatMap` cancels all involved futures #390

larsrh · 2017-07-31T20:08:37Z

Fixes #381

larsrh · 2017-07-31T20:19:05Z

Error in Travis is because of binary incompatibility. I wasn't aware that returning a more specific type could cause this.

codecov · 2017-07-31T20:47:08Z

Codecov Report

Merging #390 into master will increase coverage by 0.16%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #390      +/-   ##
==========================================
+ Coverage   87.49%   87.66%   +0.16%     
==========================================
  Files         293      293              
  Lines        8114     8112       -2     
  Branches     1156     1149       -7     
==========================================
+ Hits         7099     7111      +12     
+ Misses       1015     1001      -14

ktoso · 2017-08-01T03:15:23Z

monix-execution/shared/src/main/scala/monix/execution/FutureUtils.scala

@@ -115,18 +116,28 @@ object FutureUtils {
    *
    * Similar to `Future.transformWith` from Scala 2.12.
    */
-  def transformWith[A,B](source: Future[A], f: Try[A] => Future[B])(implicit ec: ExecutionContext): Future[B] = {
+  def transformWith[A,B](source: Future[A], f: Try[A] => Future[B])(implicit ec: ExecutionContext): CancelableFuture[B] = {


Chiming in since asked on twitter https://twitter.com/ktosopl/status/892221038242570240

This is binary incompatible, MiMa is right.
Changing the type like this will cause NoSuchMethodError.

Simple way to test those things if you think MiMa may be mistaken:

$ ls *scala it.scala lol.scala main.scala ktoso @ 三日月/tmp $ cat *scala object f { def f(): A = null } trait A trait B extends A object Main extends App { val a = f.f() } ktoso @ 三日月/tmp $ scalac *.scala ktoso @ 三日月/tmp $ java -cp /Users/ktoso/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.2.jar:. Main ktoso @ 三日月/tmp $ vim it.scala ktoso @ 三日月/tmp $ scalac it.scala ktoso @ 三日月/tmp $ cat it.scala object f { def f(): B = null } ktoso @ 三日月/tmp $ java -cp /Users/ktoso/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.12.2.jar:. Main Exception in thread "main" java.lang.NoSuchMethodError: f$.f()LA;

Hope this helps

Yeah, it helps. I'll have to rework this change to make it binary compatible.

@alexandru WDYT?

Thanks @ktoso for your input. @larsrh I've written a comment below.

Sounds like good timing if you can break now 👍

alexandru · 2017-08-01T06:36:56Z

@larsrh this change is for master and master has upgraded to depending on cats-core directly.

This means that binary compatibility is already broken heavily, because monix-cats, monix-scalaz and monix-types sub-projects are now gone, along with the instances defined for Task, Coeval and Observable. And because we are doing this, this is also a good time to get rid of deprecated methods, which lingered in the codebase for preserving compatibility.

This is why we have a big list of incompatibilities documented for 3.0.0.

So don't worry about it. If there's a time to break binary compatibility, it is now.
But Mima still serves a purpose here, because all breaking changes need to be documented.

alexandru · 2017-08-01T06:45:36Z

monix-execution/shared/src/main/scala/monix/execution/FutureUtils.scala

-    p.future
+
+    source match {
+      case c: Cancelable => cancelable.orderedUpdate(c, order = 1)


This is correct, but you already have source when initializing your val cancelable so it might be a better idea to initialize that as MultiAssignmentCancelable(source) (thus source being an initial underlying reference), because we avoid doing an Atomic.compareAndSet that way.

And so instead of the second orderedUpdate(order = 2), you can just use :=, because orderedUpdate also implies some extra logic.

Will update accordingly.

alexandru · 2017-08-01T06:46:21Z

monix-execution/shared/src/main/scala/monix/execution/FutureUtils.scala

@@ -161,6 +172,10 @@ object FutureUtils {
    p.future
  }

+  /** Creates a future that never completes. */
+  def never[A]: Future[A] =
+    Promise[A].future


Since I got notified since I chimed in about the MiMa thing thought I'll share some insight here too. Feel free to tell me to go away if you'd prefer that :-)

I would say 👎, since this can create memory leaks in the form of callbacks registered on this future, which will never trigger, however still will be registered and kept in memory.

Explanations: http://viktorklang.com/blog/Futures-in-Scala-2.12-part-6.html
Scala 2.12 solution: https://github.com/scala/scala/blob/2.12.x/src/library/scala/concurrent/Future.scala#L561

Sneaky little edge case, isn't it

I only use this for testing. I could move this to the test suite, such that nobody will accidentally use it.

The other option would be copy-pasting this from Scala into Monix, but I'm not sure whether that's a good idea.

Yeah if it's just in tests then ok I guess, would move it out from src/main though then. Your call :)

OH, I now see that it is basically never from Scala 2.12. Nice.

@alexandru I'll use that, then.

But then never from Scala 2.12 overrides everything else, e.g. flatMap.

@ktoso If we aren't overriding the other methods likeflatMap, I think that represents a potential memory leak as well.

@larsrh we might need to do a Scala 2.11 specific object (in a scala_2.11 directory) and just rely on Scala's never for 2.12.

@ktoso sorry for the noise, just wanted to mention that your input is greatly appreciated. Thanks.

No problem, cheers!

larsrh · 2017-08-01T08:27:39Z

I've addressed all feedback & Travis is green.

larsrh · 2017-08-01T11:40:37Z

@alexandru Are you planning to release milestone builds of 3.0.0?

alexandru · 2017-08-01T11:44:18Z

@larsrh yes, snapshots get published automatically whenever I merge master into snapshot.

I started a new build, when finished you should have a new version published if you want to play: https://travis-ci.org/monix/monix/builds/259733983

larsrh · 2017-08-01T12:09:03Z

Your publish script might be failing:

java.lang.IllegalStateException: Ivy file not found in cache for io.monix#monix-eval_2.11;3.0.0-27c1508!

(see build log)

alexandru · 2017-08-01T21:46:15Z

@larsrh unfortunately I've been having issues due to tooling, like Coursier, not recognizing empty projects (i.e. projects where the POM itself is the artifact,with no JAR file) and the root monix project is one.

Cannot reproduce it locally, but I've just pushed an attempted fix for it, a build is in progress: https://travis-ci.org/monix/monix/builds/259961033

alexandru · 2017-08-01T22:17:14Z

@larsrh the latest build succeeded after those fixes, you should see 3.0.0-22bf9c6 on Maven Central.

larsrh · 2017-08-02T08:41:39Z

Indeed, thanks!

drop redundant code

c5cb859

ktoso reviewed Aug 1, 2017

View reviewed changes

alexandru reviewed Aug 1, 2017

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larsrh added 2 commits August 1, 2017 10:14

flatMap is supposed to cancel the second future, too

ed6b9dd

document binary-breaking change

e21b8e2

alexandru merged commit 27c1508 into monix:master Aug 1, 2017

larsrh deleted the topic/cancel-flatmap branch August 1, 2017 11:39

alexandru added the enhancement label Jan 21, 2018

alexandru added this to the 3.0.0 milestone Jan 21, 2018

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`flatMap` cancels all involved futures #390

`flatMap` cancels all involved futures #390

larsrh commented Jul 31, 2017

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flatMap cancels all involved futures #390

flatMap cancels all involved futures #390

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larsrh commented Jul 31, 2017

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larsrh commented Aug 1, 2017

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larsrh commented Aug 2, 2017

`flatMap` cancels all involved futures #390

`flatMap` cancels all involved futures #390

codecov bot commented Jul 31, 2017 •

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ktoso Aug 1, 2017 •

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ktoso Aug 1, 2017 •

edited

ktoso Aug 1, 2017 •

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