Add reactive support

[jvalkeal]

This is a master ticket tracking reactive implementation for upcoming 3.x series. This ticket will have many sub-issues.

Main purpose of reactive support is:

• Follow the spring5/boot2 world which heavily tries to support various reactive concepts based on reactor.
• Moving away from Spring TaskExecutor if favour of getting better run-to-completion model with single-thread execution based on reactor.
• Parallel execution is mostly needed in two different places, when parallels regions are uses and when state action is executed.

Epic issues:

• Initial reactive refactor #740
• Add initial reactive Action support #743
• Refactor test to use reactive methods #744
• Deferred events not cleared in ReactiveStateMachineExecutor #747
• Refactor internals to reactive methods #750
• Generic Boot 2.2.x and Framework 5.2.x changes #765
• Add initial reactive Guard support #791
• Add reactive Trigger support #799
• Remove TaskExecutor/TaskScheduler #800
• Reactive PseudoStates #878

[jvalkeal]

I've been doing a little bit of a prototyping and having a proper reactive support means that we need to change some api's quite a bit. There's going to be breaking changes so we need to do these in a new major version.

[burakhelvaci]

You added reactive action support. Will you add reactive guard support ?

[jvalkeal]

@burakhelvaci things are very much in-progress right now, but what do you mean by reactive guard?

[jvalkeal]

Right, if you meant ReactiveGuard similar to ReactiveAction, then yes. That's not yet implemented.

[jvalkeal]

Moving this epic into RC1 as I don't expect reactive stories to be fully handled until we've travelled through milestones. Also I expect new issues to pop up after we get into first milestone.

[linux-china]

Any news for 3.0.0 release with Flux support?

[giannisapi]

Hi All, First of all great work. Any news when release 3.0.0 will be ready ?

[smartjaya]

We are looking forward to use this release, any news when 3.0.0 will be available?

[jvalkeal]

There's some documentation issue to do(which would not delay a release imho) but being honest I haven't received that much feedback about reactive features. I'm basically ready to fire a release any time.

[smartjaya]

Thank you for your response. We were trying to call a Spring Reactive Webflux endpoint in the Spring State machine, and we were not able to make the async call as they were blocking the thread. We are interested in using this release so that we can use non-blocking threads.

[gituserjava]

@jvalkeal , any information on when spring statemachine will provide support for Reactive stack?

[jvalkeal]

Closing this as final blocking issues got fixed. There's going to be RC2, and then release.