3.1.0 release preparations

[akarnokd]

Version 3.1.0 - August 9th, 2021 (Maven)

JavaDocs

⚠️ With this release, the minimum required Android API level is API 21 (Android 5.0).

⚠️ Note that the 3.0.x patch line won't be developed further.

API promotions

• Flowable.onBackpressureReduce() + 1 (#7296)
• RxJavaPlugins.getOnParallelSubscribe() and RxJavaPlugins.setOnParallelSubscribe() (#7296)
• TestScheduler([...] boolean useOnScheduleHook) (#7296)

API additions

• subscribe([...], DisposableContainer) for better Disposable management and reference cleanup. (#7298)
• RxJavaPlugins.createExecutorScheduler() for creating an Executor-based Scheduler before the Schedulers class (and thus the standard schedulers) gets initialized. (#7306)

Behavior changes

• The scheduler purge thread has been removed. Removing cancelled timed operations is now managed by the setRemoveOnCancelPolicy of the underlying ScheduledExecutorService. (#7293)

Documentation

• Fixed wording of the fair parameter of Schedulers.from. (#7301)
• Update withLatestFrom javadoc about upstream early complete (#7289)

Other

• @NonNull annotations on generic type arguments were made consistent across. (#7302, #7303)

[akarnokd]

Closing via https://github.com/ReactiveX/RxJava/releases/tag/v3.1.0