Grails and the Realtime Web

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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 (#uberfastdata) –  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 Events class  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 Events class  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