close 1.2 development and start 2.0 work

[pjfanning]

We're in the process of releasing 1.2.0-M2. There are no major issues blocking us from basically closing 1.2 development and aim for a 1.2.0 release. I would suggest waiting a month to allow people to try out the milestone release.
If we agree with this plan, we could press on with creating a 1.2.x branch and backfitting any bug fixes to this branch so that they can appear in the 1.2.0 release or a subsequent 1.2.x patch release.

This would free up the main branch and allow us to start making some bigger changes with an eventual 2.0.0 release in mind.
The 2.0.0 changes could include:

• removing some deprecated code
• removing Java 8 support - I would suggest going to Java 17 as a minimum because some of the libs that we use have already jumped to this min version and Scala 3 is planning this too. Other libs at this level include Aeron and Spring (we have a Pekko Connector for Spring). There are other libs that have jumped to Java 11 minimum too.
• possibly remove Scala 2.12 support - would possibly make it easier to support the latest Scala 3 changes (Scala 2.13 is somewhat more compatible with Scala 3)
  • this would also us to remove or deprecate some of our pekko.util classes - many are there for Scala 2.12 support and can be swapped out for classes that are available in Scala 2.13 and Scala 3 runtimes
• Look into doing something about sun.misc.Unsafe usage and generally better supporting newer Java releases
• I would prefer if we don't do anything too drastic so that our Pekko modules that were built with Pekko 1.x would still work with Pekko 2.x. This avoids having to quickly release 2.0 versions of all of the Pekko modules. Also helps the general Pekko lib ecosystem.

We will continue to fix important bugs for Pekko 1 - so I would prefer if we don't entertain too many requests to not make changes based on some users having very conservative requirements for support for old versions of Java, Scala or other 3rd party libs.

I'd be interested in everyone's opinion on these topics.

[nvollmar]

Overall I agree with those goals. 2.0 would be a good time to get rid of deprecations.
Java 17 would be a good minimum, Java 11 is already quite dated. I'd also vote for dropping Scala 2.12 support to make moving forward easier.

[He-Pin]

That's true, scala 2.12 is a pain to keep.

[He-Pin]

I am totally OK on this, one major feature of Virtual thread support is done now.

Release 1.2 and do some clean up can help further faster iterations

[raboof]

This sounds great.

I would prefer if we don't do anything too drastic so that our Pekko modules that were built with Pekko 1.x would still work with Pekko 2.x. This avoids having to quickly release 2.0 versions of all of the Pekko modules. Also helps the general Pekko lib ecosystem.

I like this goal. We might need something to make sbt happy, though: with the following test project:

scalaVersion := "2.13.16"
libraryDependencies ++= Seq(
  "org.apache.pekko" %% "pekko-actor" % "2.0.0",
  "org.apache.pekko" %% "pekko-management" % "1.1.1"
)

sbt now gives:

[error] java.lang.RuntimeException: found version conflict(s) in library dependencies; some are suspected to be binary incompatible:
[error] 
[error] 	* org.apache.pekko:pekko-actor_2.13:2.0.0 (semver-spec) is selected over {1.1.3}
[error] 	   +- default:pekko-deps_2.13:0.1.0-SNAPSHOT             (depends on 2.0.0)
[error] 	   +- org.apache.pekko:pekko-stream_2.13:1.1.3           (depends on 1.1.3)
[error] 	   +- org.apache.pekko:pekko-management_2.13:1.1.1       (depends on 1.1.3)
[error] 
[error] 
[error] this can be overridden using libraryDependencySchemes or evictionErrorLevel
[error] 	at scala.sys.package$.error(package.scala:30)
[error] 	at sbt.internal.LibraryManagement$.resolve$1(LibraryManagement.scala:90)
[error] 	at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$12(LibraryManagement.scala:142)
[error] 	at sbt.util.Tracked$.$anonfun$lastOutput$1(Tracked.scala:74)
[error] 	at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$11(LibraryManagement.scala:144)
[error] 	at sbt.internal.LibraryManagement$.$anonfun$cachedUpdate$11$adapted(LibraryManagement.scala:131)
[error] 	at sbt.util.Tracked$.$anonfun$inputChangedW$1(Tracked.scala:220)
[error] 	at sbt.internal.LibraryManagement$.cachedUpdate(LibraryManagement.scala:169)
[error] 	at sbt.Classpaths$.$anonfun$updateTask0$1(Defaults.scala:3975)
[error] 	at scala.Function1.$anonfun$compose$1(Function1.scala:49)
[error] 	at sbt.internal.util.$tilde$greater.$anonfun$$u2219$1(TypeFunctions.scala:63)
[error] 	at sbt.std.Transform$$anon$4.work(Transform.scala:69)
[error] 	at sbt.Execute.$anonfun$submit$2(Execute.scala:283)
[error] 	at sbt.internal.util.ErrorHandling$.wideConvert(ErrorHandling.scala:24)
[error] 	at sbt.Execute.work(Execute.scala:292)
[error] 	at sbt.Execute.$anonfun$submit$1(Execute.scala:283)
[error] 	at sbt.ConcurrentRestrictions$$anon$4.$anonfun$submitValid$1(ConcurrentRestrictions.scala:265)
[error] 	at sbt.CompletionService$$anon$2.call(CompletionService.scala:65)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error] 	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
[error] 	at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
[error] 	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
[error] 	at java.base/java.lang.Thread.run(Thread.java:1583)
[error] (update) found version conflict(s) in library dependencies; some are suspected to be binary incompatible:
[error] 
[error] 	* org.apache.pekko:pekko-actor_2.13:2.0.0 (semver-spec) is selected over {1.1.3}
[error] 	   +- default:pekko-deps_2.13:0.1.0-SNAPSHOT             (depends on 2.0.0)
[error] 	   +- org.apache.pekko:pekko-stream_2.13:1.1.3           (depends on 1.1.3)
[error] 	   +- org.apache.pekko:pekko-management_2.13:1.1.1       (depends on 1.1.3)
[error] 
[error] 
[error] this can be overridden using libraryDependencySchemes or evictionErrorLevel

[mdedetrich]

There are some binary breaking changes that I have planned for Pekko core 2.0.x which would mean the Pekko ecosystem would also have to be rebuilt.

Some are changes that would have ordinarily been done in the early days (i.e. Scala 3 inlining) which had to be reverted because it broke binary compatibility. There are other changes such as planned hooks for tracing/instrumentation which may require API changes (also propagate to Pekko-http)

I would personally be wary of trying to signal and hence avoid rebuilding for 2.0.x for Pekko modules as it gives the wrong impression to users. It may also be impossible as some libraries in Pekko connectors need Java 17 and at that point you may as rebuild all of Pekko for 2.0.x.

Building Pekko libraries for 2.0.x shouldn't be problem as we can just do milestone releases, it's just tedious.

[pjfanning]

I still think we are on track for doing a Pekko 1.2.0 release in a few weeks - maybe late in the month.
So far, only #1961 is a possible late breaking PR for such a release. My view is it can be merged to 1.2.0 if it is ready on time but I'd prefer not to delay the 1.2.0 release too long.

With the main branch, we are developing 2.0.0. I think it could be 6-12 months before a full release but we could do a 2.0.0-M1 in a month or 2. So far, Java 17 has become the min and about half of the old Akka-era deprecations have been removed.
One issue of potential disagreement is whether to drop Scala 2.12 support. I favour dropping it and promising to keep Pekko 1.x up to date with bug fixes.

[He-Pin]

For Scala 2.12.x support, I think if we want to keep it, we should do a quick release in Pekko 2.0.0, which ships fewer features but removes deprecated things.

And then starting to develop Pekko 2.1.x and drop Scala 2.12.x support and prepare for the next Scala 3.9.0 LTS version.

[pjfanning]

I intend to bring Scala 2.12 support to a vote in a few weeks. I think there is a reasonable chance that we could win a vote supporting removing Scala 2.12 support from Pekko 2.0.0.