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Grails and the “Real-time web”

By Stephane Maldini

Prologue

Solving a basic problem

“Your valuable users don’t like waiting”

The Age of Asynchronous

Fact #1:– HTTP request thread is critical path– Do the barely necessary for fast rendering– If it’s long*, do it in a separate thread

The Age of Asynchronous

Fact #2:– Creating new Threads needs caution– Context switching hurts performances– Concurrent programming is tricky*

The Age of Asynchronous

Fact #3:– Burden on your application is never constant– Scaling Up is a good start…– …And Scaling Out is only next

Dilemma

So I have to use background threads ?

But using them might lead to issues and headaches ?

And what if I really need to scale out ?

Reactive programming

• Adding a level of indirection : Driving your application with Events

• Laziness is key

• Scale up/out by tweaking dispatching

The big picture

Events Bus

Point to point

Service Consumer

Service Consumer

Service Consumer

Service Consumer

Service Consumer

Application

The big picture

Events Bus

Publish/Subscribe

Service Consumer

Service Consumer

Service Consumer

Service Consumer

Service Consumer

Application

The big picture

Events Bus

Publish/Subscribe

App

App

App

App

App

Cloud

Remember Platform-Core ? Remember Events ?

Introducing GRAILS-EVENTS

BOOM!

worse slide ever™

The new deal

• New features. And quite a few.– Streaming data, Selectors, Queue

• Based on a solid foundation – Reactor– Where Platform-core Events best ideas have leaked

• Semantic changes– But relatively easy migration path

So what Grails Events is about

• Grails Apps and Plugins can use Events to:– Listen for plugins/app events– Start simple with in-memory eventing– Do Asynchronous calls (default)– Increase in flexibility if required

Installing Grails Events

• It’s a binary plugin (!)• Requires Grails 2.2+

Reactor big picture

Semantics: Consumer

• A Consumer:– Accepts an Event– Is registered in a Service or Events artifact, or by calling on()– Can be thread safe

• Depending on the dispatcher type• Assuming the consumer is not registered more than once

Semantics: Selector

• A Selector:– Matches an event key– Is paired with a consumer during its registration

Semantics: Reactor

• A Reactor:– Is a dedicated Consumer Registry– Has an assigned Dispatcher– Uses a specific Event Router

•Usually, if the Dispatcher doesn’t need to be adapted, reuse the default reactor grailsReactor

Platform Core: Sending Events          def user = new User(params).save()

            //non-blocking call, will trigger application listeners for this topic            event('mailRegistration', user)             //blocking call :            //event('mailRegistration', user).waitFor()             //can also be written like that            //event topic:'mailRegistration', data:user             //and if you need to reuse the current thread            //event topic:'mailRegistration', data:user, fork:false             render(view:'sendingRegistrationMail’)

Events: Sending Events          def user = new User(params).save()

            //non-blocking call, will trigger application listeners for this topic            event('mailRegistration', user)             //Do things on each reply :            //event('mailRegistration', user){

if(it == ‘end’){ cancel() }

}  

            //can also be written like that            //event key:'mailRegistration', data:user              render(view:'sendingRegistrationMail')         

Platform Core Events : Consuming Eventsclass UserService{    //use method name 'mailRegistration' as topic name   //can also use custom topic name using topic arg: @Listener(topic='test')   @grails.events.Listener   def mailRegistration(User user){         sendMail{            to user.mail            subject "Confirmation"            html g.render(template:"userMailConfirmation")        }  }   //Can also receive an EventMessage to get more information on this particular event)  @grails.events.Listener(topic="mailRegistration")  def mailRegistration2(org.grails.plugin.platform.events.EventMessage msg){        sendMail{           to msg.data.mail           subject "Confirmation"           html g.render(template:"userMailConfirmation")        }  }}

Events : Consuming Eventsclass UserService{    //use method name 'mailRegistration' as topic name   //can also use custom topic name using topic arg: @Selector(‘test')   @reactor.spring.annotation.Selector   def mailRegistration(User user){         sendMail{            to user.mail            subject "Confirmation"            html g.render(template:"userMailConfirmation")        }  }   //Can also receive an Event to get more information on this particular event)  @reactor.spring.annotation.Selector("mailRegistration")  def mailRegistration2(reactor.event.Event msg){        sendMail{           to msg.data.mail           subject "Confirmation"           html g.render(template:"userMailConfirmation")        }  }}

Events : A new Artifact

Reactor awesomeness : Selectors

• Listen for arbitrary keys• import static reactor.event.selector.Selectors.*

Reactor awesomeness : Stream API

• Reactive Extensions programming style• Avoid callback hell

Reactor awesomeness : Promise API

• Grails 2.3 Promises become a Reactor Promises• Benefits from Dispatcher overriding• Powerful once Combined with Consumers

Reactor awesomeness : Routing

• During event dispatching, consumers list is selected• Publish Subscribe is the default• Possible to assign different routing strategy

Reactor awesomeness : Extensibility

• Main extension points:– Dispatcher, Selector, Registry, EventRouter

• Metadata in Reactor Events DSL:– ext(‘someExtension’, [ ‘doStuff’ : true ])

GORM events

• GORM is now an extension– Using ext(‘gorm’, true) on any candidate reactor– Applicable Selectors: simple topic form (beforeInsert...)– A boolean reply is evaluated as a cancel directive

GRAILS-EVENTS-PUSH

Eventing over HTTP

An elegant solution to browser push

• Powered by Atmosphere 2• Automatically picks an adapted protocol:

– WebSockets, ServerSideEvent, Streaming, Polling…

• Consumer bridges for server-to-client push• Reactor bridge for client-to-server push• Javascript library

Installing Grails Events Push

1. Install Grails Events plugin

2. Install Grails Events Push plugin

Generating Simple Browsers bridges

React on server side events

Generating Advanced Browsers bridges

DEMO

Burn some idols for the demo gods please

Epilogue

The Bad Stuff

• events-si : Events API on top of Spring Integration– Not here (just) yet

• events-vertx : Abandoned experiment– Working around Distributed Reactor

• Stream DSL could be optimized– Reducing the number of objects

Roadmap• events:

– Document, especially for Migration from Platform Core– Stick with latest awesome features from Reactor

• Still Many API to expose: Processors, Buffer, TCP, Queues, Sequencer…

• events-push -> events-atmosphere : – More robust subscription mech– Update atmosphere client– Add support for replyTo– Add support for binary

Roadmap

• events-sockjs:– Involves Reactor work here

• events-si: – Supports new events plugin

• events-xx:– The plugin where you are the hero

Learn More. Stay Connected.

• Follow-up

– Reactor repository: http://github.com/reactor/– Mail: @smaldini / smaldini@gopivotal.com

• Talk to us on Twitter: @springcentral• Find Session replays on YouTube: spring.io/video