0
@crichardson
Consuming web services asynchronously
with Futures
and Rx Observables
Chris Richardson
Author of POJOs in Act...
@crichardson
Presentation goal
Learn how to use (Scala) Futures
and Rx Observables to write
simple yet robust and scalable...
@crichardson
About Chris
@crichardson
(About Chris)
@crichardson
About Chris()
@crichardson
About Chris
@crichardson
About Chris
http://www.theregister.co.uk/2009/08/19/springsource_cloud_foundry/
@crichardson
About Chris
@crichardson
Agenda
The need for concurrency
Simplifying concurrent code with Futures
Taming callback hell with JavaScript...
@crichardson
Let’s imagine you are building an online
store
@crichardson
Shipping
Recomendations
Product
Info
Reviews
@crichardson
Reviews
Product
Info
Sales
ranking
@crichardson
Related
books
Viewing
history
Forum
@crichardson
+ mobile apps
@crichardson
Application architecture
Product Info Service
Desktop
browser
Native mobile
client
REST
REST
REST
Recomendati...
@crichardson
Handling getProductDetails()
Front-end server
Product Info Service
Recommendations
Service
Review
Service
get...
@crichardson
Handling getProductDetails() - sequentially
Front-end server
Product Info Service
Recommendations
Service
Rev...
@crichardson
Handling getProductDetails() - in parallel
Front-end server
Product Info Service
Recommendations
Service
Revi...
@crichardson
Implementing a concurrent REST client
Thread-pool based approach
executorService.submit(new Callable(...))
Si...
@crichardson
The front-end server must handle partial
failure of backend services
Front-end server
Product Info Service
Re...
@crichardson
Agenda
The need for concurrency
Simplifying concurrent code with Futures
Taming callback hell with JavaScript...
@crichardson
Futures are a great concurrency
abstraction
http://en.wikipedia.org/wiki/Futures_and_promises
@crichardson
How futures work
Outcome
Future
Client
get
Asynchronous
operation
set
initiates
@crichardson
Benefits
Client does not know how the asynchronous operation is implemented
Client can invoke multiple asynchr...
@crichardson
REST client using Spring @Async
@Component
class ProductInfoServiceImpl extends ProducInfoService {
val restT...
@crichardson
ProductDetailsService
@Component
class ProductDetailsService
@Autowired()(productInfoService: ProductInfoServ...
@crichardson
ProductController
@Controller
class ProductController
@Autowired()(productDetailsService : ProductDetailsServ...
@crichardson
Not bad but...
val productInfo =
productInfoFuture.get(300, TimeUnit.MILLISECONDS)
Blocks Tomcat thread until...
@crichardson
... and also...
Java Futures work well for a single-level of asynchronous execution
BUT
#fail for more comple...
@crichardson
Better: Futures with callbacks no blocking!
val f : Future[Int] = Future { ... }
f onSuccess {
case x : Int =...
@crichardson
Even better: Composable Futures
val f1 = Future { ... ; 1 }
val f2 = Future { ... ; 2 }
val f4 = f2.map(_ * 2...
@crichardson
Scala futures are Monads
def callB() : Future[...] = ...
def callC() : Future[...] = ...
def callD() : Future...
@crichardson
Scala Future + RestTemplate
import scala.concurrent.Future
@Component
class ProductInfoService {
def getProdu...
@crichardson
Scala Future + RestTemplate
class ProductDetailsService @Autowired()(....) {
def getProductDetails(productId:...
@crichardson
Async Spring MVC + Scala Futures
@Controller
class ProductController ... {
@RequestMapping(Array("/productdet...
@crichardson
Servlet layer is asynchronous but the
backend uses thread pools
Need event-driven REST client
@crichardson
About the Reactor pattern
Defined by Doug Schmidt in 1995
Pattern for writing scalable servers
Alternative to ...
@crichardson
Reactor pattern structure
Event Handler
handle_event(type)
get_handle()
Initiation Dispatcher
handle_events()...
@crichardson
Java NIO Selectors = Reactor pattern
But that’s super low-level :-(
@crichardson
New in Spring 4
Mirrors RestTemplate
Methods return a ListenableFuture = JDK 7 Future + callback methods
Can ...
@crichardson
Using the AsyncRestTemplate
http://hc.apache.org/httpcomponents-asyncclient-dev/
val asyncRestTemplate = new ...
@crichardson
Converting ListenableFuture to Scala Future
implicit def toScalaFuture[T](f : ListenableFuture[T]) : Future[T...
@crichardson
Now everything is non-blocking :-)
@crichardson
If recommendation service is down...
Never responds front-end server waits indefinitely
Consumes valuable fron...
@crichardson
Fault tolerance at Netflix
Network timeouts and retries
Invoke remote services via a bounded thread pool
Use t...
@crichardson
Using Hystrix
@Component
class ProductInfoServiceImpl extends ProductInfoService {
val restTemplate = RestTem...
@crichardson
But how to accomplish this with event-
driven code
@crichardson
How to handling partial failures?
productDetailsFuture zip
recommendationsFuture zip reviewsFuture
Fails if a...
@crichardson
Handling partial failures
val recommendationsFuture =
recommendationService.
getRecommendations(userId,produc...
@crichardson
Implementing a Timeout
resultFuture onSuccess { case r => result.setResult(r) }
resultFuture onFailure { case...
@crichardson
Non-blocking Timeout
http://eng.42go.com/future-safefuture-timeout-cancelable/
object TimeoutFuture {
def app...
@crichardson
Using the Akka Circuit Breaker
import akka.pattern.CircuitBreaker
val breaker =
new CircuitBreaker(actorSyste...
@crichardson
Limiting # of simultaneous requests
val limiter =
new ConcurrencyLimiter(maxConcurrentRequests=10, maxQueueSi...
@crichardson
Putting it all together
@Component
class ProductInfoServiceImpl @Autowired()(...) extends ProductService {
va...
@crichardson
Agenda
The need for concurrency
Simplifying concurrent code with Futures
Taming callback hell with JavaScript...
@crichardson
@crichardson
Why solve this problem for JavaScript?
Browser invokes web services
Implement front-end server/API gateway us...
@crichardson
What’s NodeJS?
Designed for DIRTy apps
@crichardson
NodeJS
JavaScript
Reactor
pattern
Modules
@crichardson
Asynchronous JavaScript code =
callback hell
Scenarios:
Sequential: A B C
Fork and join: A and B C
Code quick...
@crichardson
Callback-based HTTP client
request = require("request")
handler = (error, clientResponse, body) ->
if clientR...
@crichardson
Messy callback code
getProductDetails = (req, res) ->
productId = req.params.productId
result = {productId: p...
@crichardson
Simplifying code with Promises (a.k.a.
Futures)
Functions return a promise - no callback parameter
A promise ...
@crichardson
Basic promise API
promise2 = promise1.then(fulfilledHandler, errorHandler, ...)
called when promise1 is fulfil...
About when.js
Rich API = Promises spec + use full
extensions
Creation:
when.defer()
when.reject()...
Combinators:
all, som...
@crichardson
Simpler promise-based code
rest = require("rest")
@httpClient = rest.chain(mime).chain(errorCode);
getProduct...
@crichardson
Simpler promise-based code
class ProductDetailsService
getProductDetails: (productId) ->
makeProductDetails =...
@crichardson
Simpler promise-based code: HTTP
handler
getProductDetails = (req, res) ->
productId = req.params.productId
s...
@crichardson
Writing robust client code
@crichardson
Implementing timeouts
timeout = require("when/timeout")
withTimeout = (promise) -> timeout(300, promise)
getP...
@crichardson
Recovering from failures
getRecommendations(productId).otherwise( -> {})
Invoked to return default value if g...
@crichardson
Limiting # of concurrent requests
ConcurrencyLimiter = require("./concurrencylimiter").ConcurrencyLimiter
lim...
@crichardson
Circuit breaker
CircuitBreaker = require("./circuitbreaker").CircuitBreaker
productCircuitBreaker = new Circu...
@crichardson
Putting it all together
getProductDetails: (productId) ->
...
responses = [@getProductInfo(productId),
@getRe...
@crichardson
Agenda
The need for concurrency
Simplifying concurrent code with Futures
Taming callback hell with JavaScript...
@crichardson
Let’s imagine you have a stream of trades
and
you need to calculate the rolling average
price of each stock
@crichardson
Spring Integration + Complex event
processing (CEP) engine is a good
choice
@crichardson
But where is the high-level abstraction
that solves this problem?
@crichardson
Future[List[T]]
Not applicable to infinite streams
@crichardson
Introducing Reactive Extensions (Rx)
The Reactive Extensions (Rx) is a library for composing
asynchronous and...
@crichardson
About RxJava
Reactive Extensions (Rx) for the JVM
Implemented in Java
Adaptors for Scala, Groovy and Clojure
...
@crichardson
RxJava core concepts
class Observable<T> {
Subscription subscribe(Observer<T> observer)
...
}
interface Obser...
@crichardson
Comparing Observable to...
Observer pattern - similar but adds
Observer.onComplete()
Observer.onError()
Itera...
@crichardson
So what?
@crichardson
Transforming Observables
class Observable<T> {
Observable<T> take(int n);
Observable<T> skip(int n);
<R> Obse...
@crichardson
Transforming observables
class Observable<T> {
<K> Observable<GroupedObservable<K,T>>
groupBy(Func1<T,K> keyS...
@crichardson
Combining observables
class Observable<T> {
static <R,T1,T2>
Observable<R> zip(Observable<T0> o1,
Observable<...
@crichardson
Creating observables from data
class Observable<T> {
static Observable<T> from(Iterable<T> iterable]);
static...
@crichardson
Creating observables from event sources
Observable<T> o = Observable.create(
new SubscriberFunc<T> () {
Subsc...
@crichardson
Using Rx Observables instead of
Futures
@crichardson
Rx-based ProductInfoService
@Component
class ProductInfoService
override def getProductInfo(productId: Long) ...
@crichardson
ListenableFuture Observable
implicit def toRxObservable[T](future: ListenableFuture[T])
: Observable[T] = {
d...
@crichardson
Rx - ProductDetailsService
@Component
class ProductDetailsService @Autowired()
(productInfoService: ProductIn...
@crichardson
Rx - ProductController
@Controller
class ProductController
@RequestMapping(Array("/productdetails/{productId}...
@crichardson
Rx - Observable DeferredResult
implicit def toDeferredResult[T](observable : Observable[T]) = {
val result = ...
@crichardson
RxObservables vs. Futures
Much better than JDK 7 futures
Comparable to Scala Futures
Rx Scala code is slightl...
@crichardson
Making this code robust
Hystrix works with Observables (and thread pools)
But
For event-driven code we are on...
@crichardson
Back to the stream of Trades averaging
example...
@crichardson
AMQP messages Observables 1
<amqp:inbound-channel-adapter ... />
<int:channel id="inboundEventsChannel"/>
<in...
@crichardson
AMQP messages Observables 2
class AmqpToObservableAdapter (actorRef : observerManager) {
def createObservable...
@crichardson
Calculating averages
Observable<AveragePrice>
calculateAverages(Observable<Trade> trades) {
...
}
class Trade...
@crichardson
Using groupBy()
APPL : 401 IBM : 405 CAT : 405 APPL: 403
groupBy( (trade) => trade.symbol)
APPL : 401
IBM : 4...
@crichardson
Using window()
APPL : 401 APPL : 405 APPL : 405 ...
APPL : 401 APPL : 405 APPL : 405
APPL : 405 APPL : 405 AP...
@crichardson
Using reduce()
APPL : 402 APPL : 405 APPL : 405
APPL : 404
reduce(sumCalc) / length
Observable<Trade>
Observa...
@crichardson
Using merge()
merge()
APPL : 401
IBM : 405
CAT : 405 ...
APPL: 403
APPL : 401 IBM : 405 CAT : 405 APPL: 403
O...
@crichardson
RxJS / NodeJS example
var rx = require("rx");
function tailFile (fileName) {
var self = this;
var o = rx.Obse...
@crichardson
Rx in the browser - implementing
completion
TextChanges(input)
.DistinctUntilChanged()
.Throttle(TimeSpan.Fro...
@crichardson
Summary
Consuming web services asynchronously is essential
Scala-style composable Futures are a powerful conc...
@crichardson
Questions?
@crichardson chris@chrisrichardson.net
http://plainoldobjects.com
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Futures and Rx Observables: powerful abstractions for consuming web services asynchronously (#springone #s2gx)

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A modular, polyglot architecture has many advantages but it also adds complexity since each incoming request typically fans out to multiple distributed services. For example, in an online store application the information on a product details page - description, price, recommendations, etc - comes from numerous services. To minimize response time and improve scalability, these services must be invoked concurrently. However, traditional concurrency mechanisms are low-level, painful to use and error-prone.

In this talk you will learn about some powerful yet easy to use abstractions for consuming web services asynchronously. We will compare the various implementations of futures that are available in Java, Scala and JavaScript. You will learn how to use reactive observables, which are asynchronous data streams, to access web services from both Java and JavaScript. We will describe how these mechanisms let you write asynchronous code in a very straightforward, declarative fashion.

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Transcript of "Futures and Rx Observables: powerful abstractions for consuming web services asynchronously (#springone #s2gx)"

  1. 1. @crichardson Consuming web services asynchronously with Futures and Rx Observables Chris Richardson Author of POJOs in Action Founder of the original CloudFoundry.com @crichardson chris@chrisrichardson.net http://plainoldobjects.com
  2. 2. @crichardson Presentation goal Learn how to use (Scala) Futures and Rx Observables to write simple yet robust and scalable concurrent code
  3. 3. @crichardson About Chris
  4. 4. @crichardson (About Chris)
  5. 5. @crichardson About Chris()
  6. 6. @crichardson About Chris
  7. 7. @crichardson About Chris http://www.theregister.co.uk/2009/08/19/springsource_cloud_foundry/
  8. 8. @crichardson About Chris
  9. 9. @crichardson Agenda The need for concurrency Simplifying concurrent code with Futures Taming callback hell with JavaScript promises Consuming asynchronous streams with Reactive Extensions
  10. 10. @crichardson Let’s imagine you are building an online store
  11. 11. @crichardson Shipping Recomendations Product Info Reviews
  12. 12. @crichardson Reviews Product Info Sales ranking
  13. 13. @crichardson Related books Viewing history Forum
  14. 14. @crichardson + mobile apps
  15. 15. @crichardson Application architecture Product Info Service Desktop browser Native mobile client REST REST REST Recomendation Service Review Service Front end server API gatewayREST Mobile browser Web Application HTML
  16. 16. @crichardson Handling getProductDetails() Front-end server Product Info Service Recommendations Service Review Service getProductInfo() getRecommendations() getReviews() getProductDetails()
  17. 17. @crichardson Handling getProductDetails() - sequentially Front-end server Product Info Service Recommendations Service Review Service getProductInfo() getRecommendations() getReviews() getProductDetails() Higher response time :-(
  18. 18. @crichardson Handling getProductDetails() - in parallel Front-end server Product Info Service Recommendations Service Review Service getProductInfo() getRecommendations() getReviews() getProductDetails() Lower response time :-)
  19. 19. @crichardson Implementing a concurrent REST client Thread-pool based approach executorService.submit(new Callable(...)) Simpler but less scalable - lots of idle threads consuming memory Event-driven approach NIO with completion callbacks More complex but more scalable
  20. 20. @crichardson The front-end server must handle partial failure of backend services Front-end server Product Info Service Recommendations Service Review Service getProductInfo() getRecommendations() getReviews() getProductDetails() X How to provide a good user experience?
  21. 21. @crichardson Agenda The need for concurrency Simplifying concurrent code with Futures Taming callback hell with JavaScript promises Consuming asynchronous streams with Reactive Extensions
  22. 22. @crichardson Futures are a great concurrency abstraction http://en.wikipedia.org/wiki/Futures_and_promises
  23. 23. @crichardson How futures work Outcome Future Client get Asynchronous operation set initiates
  24. 24. @crichardson Benefits Client does not know how the asynchronous operation is implemented Client can invoke multiple asynchronous operations and gets a Future for each one.
  25. 25. @crichardson REST client using Spring @Async @Component class ProductInfoServiceImpl extends ProducInfoService { val restTemplate : RestTemplate = ... @Async def getProductInfo(productId: Long) = { new AsyncResult(restTemplate.getForObject(....)...) } } Execute asynchronously in thread pool A Future containing a value trait ProductInfoService { def getProductInfo(productId: Long): java.util.concurrent.Future[ProductInfo] }
  26. 26. @crichardson ProductDetailsService @Component class ProductDetailsService @Autowired()(productInfoService: ProductInfoService, reviewService: ReviewService, recommendationService: RecommendationService) { def getProductDetails(productId: Long): ProductDetails = { val productInfoFuture = productInfoService.getProductInfo(productId) } } val recommendationsFuture = recommendationService.getRecommendations(productId) val reviewsFuture = reviewService.getReviews(productId) val productInfo = productInfoFuture.get(300, TimeUnit.MILLISECONDS) val recommendations = recommendationsFuture.get(10, TimeUnit.MILLISECONDS) val reviews = reviewsFuture.get(10, TimeUnit.MILLISECONDS) ProductDetails(productInfo, recommendations, reviews)
  27. 27. @crichardson ProductController @Controller class ProductController @Autowired()(productDetailsService : ProductDetailsService) { @RequestMapping(Array("/productdetails/{productId}")) @ResponseBody def productDetails(@PathVariable productId: Long) = productDetailsService.getProductDetails(productId)
  28. 28. @crichardson Not bad but... val productInfo = productInfoFuture.get(300, TimeUnit.MILLISECONDS) Blocks Tomcat thread until Future completes Not so scalable :-(
  29. 29. @crichardson ... and also... Java Futures work well for a single-level of asynchronous execution BUT #fail for more complex, scalable scenarios Difficult to compose and coordinate multiple concurrent operations http://techblog.netflix.com/2013/02/rxjava-netflix-api.html
  30. 30. @crichardson Better: Futures with callbacks no blocking! val f : Future[Int] = Future { ... } f onSuccess { case x : Int => println(x) } f onFailure { case e : Exception => println("exception thrown") } Guava ListenableFutures, Spring 4 ListenableFuture Java 8 CompletableFuture, Scala Futures
  31. 31. @crichardson Even better: Composable Futures val f1 = Future { ... ; 1 } val f2 = Future { ... ; 2 } val f4 = f2.map(_ * 2) assertEquals(4, Await.result(f4, 1 second)) val fzip = f1 zip f2 assertEquals((1, 2), Await.result(fzip, 1 second)) Transforms Future Combines two futures Scala, Java 8 CompletableFuture (partially)
  32. 32. @crichardson Scala futures are Monads def callB() : Future[...] = ... def callC() : Future[...] = ... def callD() : Future[...] = ... val result = for { (b, c) <- callB() zip callC(); d <- callD(b, c) } yield d result onSuccess { .... } Two calls execute in parallel And then invokes D Get the result of D
  33. 33. @crichardson Scala Future + RestTemplate import scala.concurrent.Future @Component class ProductInfoService { def getProductInfo(productId: Long): Future[ProductInfo] = { Future { restTemplate.getForObject(....) } } } Executes in thread pool Scala Future
  34. 34. @crichardson Scala Future + RestTemplate class ProductDetailsService @Autowired()(....) { def getProductDetails(productId: Long) = { val productInfoFuture = productInfoService.getProductInfo(productId) val recommendationsFuture = recommendationService.getRecommendations(productId) val reviewsFuture = reviewService.getReviews(productId) for (((productInfo, recommendations), reviews) <- productInfoFuture zip recommendationsFuture zip reviewsFuture) yield ProductDetails(productInfo, recommendations, reviews) } } Non-blocking!
  35. 35. @crichardson Async Spring MVC + Scala Futures @Controller class ProductController ... { @RequestMapping(Array("/productdetails/{productId}")) @ResponseBody def productDetails(@PathVariable productId: Long) = { val productDetails = productDetailsService.getProductDetails(productId) val result = new DeferredResult[ProductDetails] productDetails onSuccess { case r => result.setResult(r) } productDetails onFailure { case t => result.setErrorResult(t) } result } Convert Scala Future to Spring MVC DeferredResult
  36. 36. @crichardson Servlet layer is asynchronous but the backend uses thread pools Need event-driven REST client
  37. 37. @crichardson About the Reactor pattern Defined by Doug Schmidt in 1995 Pattern for writing scalable servers Alternative to thread-per-connection model Single threaded event loop dispatches events on handles (e.g. sockets, file descriptors) to event handlers
  38. 38. @crichardson Reactor pattern structure Event Handler handle_event(type) get_handle() Initiation Dispatcher handle_events() register_handler(h) select(handlers) for each h in handlers h.handle_event(type) end loop handle Synchronous Event Demultiplexer select() owns notifies uses handlers Application creates
  39. 39. @crichardson Java NIO Selectors = Reactor pattern But that’s super low-level :-(
  40. 40. @crichardson New in Spring 4 Mirrors RestTemplate Methods return a ListenableFuture = JDK 7 Future + callback methods Can use HttpComponents NIO-based AsyncHttpClient Spring AsyncRestTemplate
  41. 41. @crichardson Using the AsyncRestTemplate http://hc.apache.org/httpcomponents-asyncclient-dev/ val asyncRestTemplate = new AsyncRestTemplate( new HttpComponentsAsyncClientHttpRequestFactory()) override def getProductInfo(productId: Long) = { val listenableFuture = asyncRestTemplate.getForEntity("{baseUrl}/productinfo/{productId}", classOf[ProductInfo], baseUrl, productId) toScalaFuture(listenableFuture).map { _.getBody } } Convert to Scala Future and get entity
  42. 42. @crichardson Converting ListenableFuture to Scala Future implicit def toScalaFuture[T](f : ListenableFuture[T]) : Future[T] = { val p = promise[T] f.addCallback(new ListenableFutureCallback[T] { def onSuccess(result: T) { p.success(result)} def onFailure(t: Throwable) { p.failure(t) } }) p.future } The producer side of Scala Futures Supply outcome Return future
  43. 43. @crichardson Now everything is non-blocking :-)
  44. 44. @crichardson If recommendation service is down... Never responds front-end server waits indefinitely Consumes valuable front-end server resources Page never displayed and customer gives up Returns an error Error returned to the front-end server error page is displayed Customer gives up
  45. 45. @crichardson Fault tolerance at Netflix Network timeouts and retries Invoke remote services via a bounded thread pool Use the Circuit Breaker pattern On failure: return default/cached data return error to caller Implementation: https://github.com/Netflix/Hystrix http://techblog.netflix.com/2012/02/fault-tolerance-in-high-volume.html
  46. 46. @crichardson Using Hystrix @Component class ProductInfoServiceImpl extends ProductInfoService { val restTemplate = RestTemplateFactory.makeRestTemplate() val baseUrl = ... class GetProductInfoCommand(productId: Long)extends HystrixCommand[ProductInfo](....) { override def run() = restTemplate. getForEntity("{baseUrl}/productinfo/{productId}", classOf[ProductInfo], baseUrl, productId).getBody } def getProductInfoUsingHystrix(productId: Long) : Future[ProductInfo] = { new GetProductInfoCommand(productId).queue() } } Runs in thread pool Returns JDK Future
  47. 47. @crichardson But how to accomplish this with event- driven code
  48. 48. @crichardson How to handling partial failures? productDetailsFuture zip recommendationsFuture zip reviewsFuture Fails if any Future has failed
  49. 49. @crichardson Handling partial failures val recommendationsFuture = recommendationService. getRecommendations(userId,productId). recover { case _ => Recommendations(List()) } “catch-like” Maps Throwable to value
  50. 50. @crichardson Implementing a Timeout resultFuture onSuccess { case r => result.setResult(r) } resultFuture onFailure { case t => result.setErrorResult(t) } No timeout - callbacks might never be invoked :-( Await.result(resultFuture, timeout) Blocks until timeout:-(
  51. 51. @crichardson Non-blocking Timeout http://eng.42go.com/future-safefuture-timeout-cancelable/ object TimeoutFuture { def apply[T](future: Future[T], onTimeout: => Unit = Unit) (implicit ec: ExecutionContext, after: Duration): Future[T] = { val timer = new HashedWheelTimer(10, TimeUnit.MILLISECONDS) val promise = Promise[T]() val timeout = timer.newTimeout(new TimerTask { def run(timeout: Timeout){ onTimeout promise.failure(new TimeoutException(s"Future timed out after ${after.toMillis}ms")) } }, after.toNanos, TimeUnit.NANOSECONDS) Future.firstCompletedOf(Seq(future, promise.future)). tap(_.onComplete { case result => timeout.cancel() }) } } val future = ... val timedoutFuture = TimeoutFuture(future)(executionContext, 200.milleseconds) Timer fails promise Outcome of first completed
  52. 52. @crichardson Using the Akka Circuit Breaker import akka.pattern.CircuitBreaker val breaker = new CircuitBreaker(actorSystem.scheduler, maxFailures = 1, callTimeout = 100.milliseconds, resetTimeout = 1.minute) val resultFuture = breaker. withCircuitBreaker{ asynchronousOperationReturningFuture() }
  53. 53. @crichardson Limiting # of simultaneous requests val limiter = new ConcurrencyLimiter(maxConcurrentRequests=10, maxQueueSize=30) val resultFuture = limiter.withLimit { asynchronousOperationReturningFuture() } class ConcurrencyLimiter ... val concurrencyManager : ActorRef = ... def withLimit[T](body : => Future[T])(...) = (concurrencyManager ? ConcurrentExecutionManager.Request { () => body }).mapTo[T]
  54. 54. @crichardson Putting it all together @Component class ProductInfoServiceImpl @Autowired()(...) extends ProductService { val limiter = new ConcurrencyLimiter(...) val breaker = new CircuitBreaker(...) override def getProductInfo(productId: Long) = { ... breaker.withCircuitBreaker { limiter.withLimit { TimeoutFuture { ... AsyncRestTemplate.get ... } } } }
  55. 55. @crichardson Agenda The need for concurrency Simplifying concurrent code with Futures Taming callback hell with JavaScript promises Consuming asynchronous streams with Reactive Extensions
  56. 56. @crichardson
  57. 57. @crichardson Why solve this problem for JavaScript? Browser invokes web services Implement front-end server/API gateway using NodeJS!
  58. 58. @crichardson What’s NodeJS? Designed for DIRTy apps
  59. 59. @crichardson NodeJS JavaScript Reactor pattern Modules
  60. 60. @crichardson Asynchronous JavaScript code = callback hell Scenarios: Sequential: A B C Fork and join: A and B C Code quickly becomes very messy
  61. 61. @crichardson Callback-based HTTP client request = require("request") handler = (error, clientResponse, body) -> if clientResponse.statusCode != 200 // ERROR else // SUCCESS request("http://.../productdetails/" + productId, handler)
  62. 62. @crichardson Messy callback code getProductDetails = (req, res) -> productId = req.params.productId result = {productId: productId} makeHandler = (key) -> (error, clientResponse, body) -> if clientResponse.statusCode != 200 res.status(clientResponse.statusCode) res.write(body) res.end() else result[key] = JSON.parse(body) if (result.productInfo and result.recommendations and result.reviews) res.json(result) request("http://localhost:3000/productdetails/" + productId, makeHandler("productInfo")) request("http://localhost:3000/recommendations/" + productId, makeHandler('recommendations')) request("http://localhost:3000/reviews/" + productId, makeHandler('reviews')) app.get('/productinfo/:productId', getProductInfo) Returns a callback function Have all three requests completed?
  63. 63. @crichardson Simplifying code with Promises (a.k.a. Futures) Functions return a promise - no callback parameter A promise represents an eventual outcome Use a library of functions for transforming and composing promises Promises/A+ specification - http://promises-aplus.github.io/promises-spec
  64. 64. @crichardson Basic promise API promise2 = promise1.then(fulfilledHandler, errorHandler, ...) called when promise1 is fulfilled returns a promise or value resolved with outcome of callback called when promise1 is rejected returns a promise or value
  65. 65. About when.js Rich API = Promises spec + use full extensions Creation: when.defer() when.reject()... Combinators: all, some, join, map, reduce Other: Calling non-promise code timeout .... https://github.com/cujojs/when
  66. 66. @crichardson Simpler promise-based code rest = require("rest") @httpClient = rest.chain(mime).chain(errorCode); getProductInfo : (productId) -> @httpClient path: "http://.../productinfo/" + productId Returns a promise No ugly callbacks
  67. 67. @crichardson Simpler promise-based code class ProductDetailsService getProductDetails: (productId) -> makeProductDetails = (productInfo, recommendations, reviews) -> details = productId: productId productDetails: productInfo.entity recommendations: recommendations.entity reviews: reviews.entity details responses = [@getProductInfo(productId), @getRecommendations(productId), @getReviews(productId)] all(responses).spread(makeProductDetails) Array[Promise] Promise[Array]
  68. 68. @crichardson Simpler promise-based code: HTTP handler getProductDetails = (req, res) -> productId = req.params.productId succeed = (productDetails) -> res.json(productDetails) fail = (something) -> res.send(500, JSON.stringify(something.entity || something)) productDetailsService. getDetails(productId). then(succeed, fail) app.get('/productdetails/:productId', getProductDetails)
  69. 69. @crichardson Writing robust client code
  70. 70. @crichardson Implementing timeouts timeout = require("when/timeout") withTimeout = (promise) -> timeout(300, promise) getProductDetails = (productId) -> ... withTimeout(client(...)) Creates a new promise Original promise must complete within 300 msec
  71. 71. @crichardson Recovering from failures getRecommendations(productId).otherwise( -> {}) Invoked to return default value if getRecommendations() fails
  72. 72. @crichardson Limiting # of concurrent requests ConcurrencyLimiter = require("./concurrencylimiter").ConcurrencyLimiter limiter = new ConcurrencyLimiter(maxQueueSize = 100, maxConcurrency = 10) getProductDetails = (productId) -> ... limiter.withLimit( -> client(...)) Homegrown code
  73. 73. @crichardson Circuit breaker CircuitBreaker = require("./circuitbreaker").CircuitBreaker productCircuitBreaker = new CircuitBreaker() getProductDetails = (productId) -> ... productCircuitBreaker.withCircuitBreaker( -> client(...)) Homegrown code
  74. 74. @crichardson Putting it all together getProductDetails: (productId) -> ... responses = [@getProductInfo(productId), @getRecommendations(productId).otherwise(() -> {}), @getReviews(productId).otherwise(() -> {})] all(responses).spread(succeed) getProductInfo = (productId) -> limiter.withLimit -> productCircuitBreaker.withCircuitBreaker -> withTimeout client path: "http://..../productinfo/" + productd
  75. 75. @crichardson Agenda The need for concurrency Simplifying concurrent code with Futures Taming callback hell with JavaScript promises Consuming asynchronous streams with Reactive Extensions
  76. 76. @crichardson Let’s imagine you have a stream of trades and you need to calculate the rolling average price of each stock
  77. 77. @crichardson Spring Integration + Complex event processing (CEP) engine is a good choice
  78. 78. @crichardson But where is the high-level abstraction that solves this problem?
  79. 79. @crichardson Future[List[T]] Not applicable to infinite streams
  80. 80. @crichardson Introducing Reactive Extensions (Rx) The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators. Using Rx, developers represent asynchronous data streams with Observables , query asynchronous data streams using LINQ operators , and ..... https://rx.codeplex.com/
  81. 81. @crichardson About RxJava Reactive Extensions (Rx) for the JVM Implemented in Java Adaptors for Scala, Groovy and Clojure https://github.com/Netflix/RxJava
  82. 82. @crichardson RxJava core concepts class Observable<T> { Subscription subscribe(Observer<T> observer) ... } interface Observer<T> { void onNext(T args) void onCompleted() void onError(Throwable e) } Notifies An asynchronous stream of items Used to unsubscribe
  83. 83. @crichardson Comparing Observable to... Observer pattern - similar but adds Observer.onComplete() Observer.onError() Iterator pattern - mirror image Push rather than pull Future - similar but Represents a stream of multiple values
  84. 84. @crichardson So what?
  85. 85. @crichardson Transforming Observables class Observable<T> { Observable<T> take(int n); Observable<T> skip(int n); <R> Observable<R> map(Func1<T,R> func) <R> Observable<R> flatMap(Func1<T,Observable<R>> func) Observable<T> filter(Func1<T,java.lang.Boolean> predicate) ... } Scala-collection style methods
  86. 86. @crichardson Transforming observables class Observable<T> { <K> Observable<GroupedObservable<K,T>> groupBy(Func1<T,K> keySelector) ... } Similar to Scala groupBy except results are emitted as items arrive Stream of streams!
  87. 87. @crichardson Combining observables class Observable<T> { static <R,T1,T2> Observable<R> zip(Observable<T0> o1, Observable<T1> o2, Func2<T1,T2,R> reduceFunction) ... } Invoked with pairs of items from o1 and o2 Stream of results from reduceFunction
  88. 88. @crichardson Creating observables from data class Observable<T> { static Observable<T> from(Iterable<T> iterable]); static Observable<T> from(T items ...]); static Observable<T> from(Future<T> future]); ... }
  89. 89. @crichardson Creating observables from event sources Observable<T> o = Observable.create( new SubscriberFunc<T> () { Subscription onSubscribe(Observer<T> obs) { ... connect to event source.... return new Subscriber () { void unsubscribe() { ... }; }; }); Called once for each Observer Called when unsubscribing Arranges to call obs.onNext/onComplete/...
  90. 90. @crichardson Using Rx Observables instead of Futures
  91. 91. @crichardson Rx-based ProductInfoService @Component class ProductInfoService override def getProductInfo(productId: Long) = { val baseUrl = ... val responseEntity = asyncRestTemplate.getForEntity(baseUrl + "/productinfo/{productId}", classOf[ProductInfo], productId) toRxObservable(responseEntity).map { (r : ResponseEntity[ProductInfo]) => r.getBody } }
  92. 92. @crichardson ListenableFuture Observable implicit def toRxObservable[T](future: ListenableFuture[T]) : Observable[T] = { def create(o: Observer[T]) = { future.addCallback(new ListenableFutureCallback[T] { def onSuccess(result: T) { o.onNext(result) o.onCompleted() } def onFailure(t: Throwable) { o.onError(t) } }) new Subscription { def unsubscribe() {} } } Observable.create(create _) } Supply single value Indicate failure Do nothing
  93. 93. @crichardson Rx - ProductDetailsService @Component class ProductDetailsService @Autowired() (productInfoService: ProductInfoService, reviewService: ReviewService, ecommendationService: RecommendationService) { def getProductDetails(productId: Long) = { val productInfo = productInfoService.getProductInfo(productId) val recommendations = recommendationService.getRecommendations(productId) val reviews = reviewService.getReviews(productId) Observable.zip(productInfo, recommendations, reviews, (p : ProductInfo, r : Recommendations, rv : Reviews) => ProductDetails(p, r, rv)) } } Just like Scala Futures
  94. 94. @crichardson Rx - ProductController @Controller class ProductController @RequestMapping(Array("/productdetails/{productId}")) @ResponseBody def productDetails(@PathVariable productId: Long) = toDeferredResult(productDetailsService.getProductDetails(productId))
  95. 95. @crichardson Rx - Observable DeferredResult implicit def toDeferredResult[T](observable : Observable[T]) = { val result = new DeferredResult[T] observable.subscribe(new Observer[T] { def onCompleted() {} def onError(e: Throwable) { result.setErrorResult(e) } def onNext(r: T) { result.setResult(r.asInstanceOf[T]) } }) result }
  96. 96. @crichardson RxObservables vs. Futures Much better than JDK 7 futures Comparable to Scala Futures Rx Scala code is slightly more verbose
  97. 97. @crichardson Making this code robust Hystrix works with Observables (and thread pools) But For event-driven code we are on our own
  98. 98. @crichardson Back to the stream of Trades averaging example...
  99. 99. @crichardson AMQP messages Observables 1 <amqp:inbound-channel-adapter ... /> <int:channel id="inboundEventsChannel"/> <int:service-activator input-channel="inboundEventsChannel" ref="amqpToObservableAdapter" method="handleMessage"/>
  100. 100. @crichardson AMQP messages Observables 2 class AmqpToObservableAdapter (actorRef : observerManager) { def createObservable() = Observable.create((o: Observer[_ >: String]) => { observerManager ! Subscribe(o) new Subscription { override def unsubscribe() { observerManager ! Unsubscribe(o) } } }) def handleMessage(message : String) { observerManager ! Message(message) } } Manages and notifies observers
  101. 101. @crichardson Calculating averages Observable<AveragePrice> calculateAverages(Observable<Trade> trades) { ... } class Trade { private String symbol; private double price; class AveragePrice { private String symbol; private double averagePrice;
  102. 102. @crichardson Using groupBy() APPL : 401 IBM : 405 CAT : 405 APPL: 403 groupBy( (trade) => trade.symbol) APPL : 401 IBM : 405 CAT : 405 ... APPL: 403 Observable<GroupedObservable<String, Trade>> Observable<Trade>
  103. 103. @crichardson Using window() APPL : 401 APPL : 405 APPL : 405 ... APPL : 401 APPL : 405 APPL : 405 APPL : 405 APPL : 405 APPL : 403 APPL : 405 ... window(...) Observable<Trade> Observable<Observable<Trade>> N secs N secs M secs
  104. 104. @crichardson Using reduce() APPL : 402 APPL : 405 APPL : 405 APPL : 404 reduce(sumCalc) / length Observable<Trade> Observable<AveragePrice> Singleton
  105. 105. @crichardson Using merge() merge() APPL : 401 IBM : 405 CAT : 405 ... APPL: 403 APPL : 401 IBM : 405 CAT : 405 APPL: 403 Observable<Observable<AveragePrice>> Observable<AveragePrice>
  106. 106. @crichardson RxJS / NodeJS example var rx = require("rx"); function tailFile (fileName) { var self = this; var o = rx.Observable.create(function (observer) { var watcher = self.tail(fileName, function (line) { observer.onNext(line); }); return function () { watcher.close(); } }); return o.map(parseLogLine); } function parseLogLine(line) { ... }
  107. 107. @crichardson Rx in the browser - implementing completion TextChanges(input) .DistinctUntilChanged() .Throttle(TimeSpan.FromMilliSeconds(10)) .Select(word=>Completions(word)) .Switch() .Subscribe(ObserveChanges(output)); Your Mouse is a Database http://queue.acm.org/detail.cfm?id=2169076 Ajax call returning Observable Change events Observable Display completions
  108. 108. @crichardson Summary Consuming web services asynchronously is essential Scala-style composable Futures are a powerful concurrency abstraction Rx Observables are even more powerful Rx Observables are a unifying abstraction for a wide variety of use cases
  109. 109. @crichardson Questions? @crichardson chris@chrisrichardson.net http://plainoldobjects.com
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