Rx workshop

Reactive ExtensionsWorkshopRyan Riley & Wes Dyer

Logistics30 minute sections10 minutes presentation10 minutes coding10 minutes discussionNew partner every sectionPrizes for best code during each section

Where can I get them?Install with NuGetDownload at MSDN Data Developer Center

OutlineIntroduction to RxA Unified Programming ModelThe Power of RxRxJSSchedulersEvent ProcessingReactive CoincidenceContinuations EverywhereProgramming the Cloud

introduction to rxlike events but much better

The Reactive ExtensionsRx is …a set of types representing asynchronous data streamsa set of operators to query asynchronous data streamsa set of types to parameterize concurrencyRx = Observables + LINQ + Schedulers

Reactive ProgrammingIn computing, reactive programming is a programming paradigm oriented around data flows and the propagation of change.http://en.wikipedia.org/wiki/Reactive_programming

Why should I care?GPSRSS feedsStock tickersSocialmediaUI eventsServer management

Reactive Programming using EventsDeclareeventAction<int> E;PublishE(42);Subscribe E += x => Console.WriteLine(x);

Reactive Programming using RxDeclareISubject<int> S = newSubject<int>();PublishS.OnNext(42);SubscribeS.Subscribe(x => Console.WriteLine(x));

classProgram {ISubject<int> S = newSubject<int>();static void Main() {var p = newProgram();p.S.Subscribe(x => Console.WriteLine(x));p.S.OnNext(1);p.S.OnNext(2);p.S.OnNext(3); }}classProgram {eventAction<int> E;static void Main() {var p = newProgram();p.E += x => Console.WriteLine(x);p.E(1);p.E(2);p.E(3); }}A Little Example

Separate Publish from Subscribe BothPublishSubscribe

First-Class “Events”An object is first-class when it:can be stored in variables and data structurescan be passed as a parameter to a subroutinecan be returned as the result of a subroutinecan be constructed at runtimehas intrinsic identity (independent of any given name)http://en.wikipedia.org/wiki/First-class_object

First-Class “Events”// storedIObservable<string> textChanged = …;// passedvoidProcessRequests(IObservable<string> input) {…}// returnedIObservable<int> QueryServer() {…}

PunctuationclassIObserver<in T>{voidOnNext(T value);voidOnError(Exception error);voidOnCompleted();}

ContractGrammar: OnNext* [OnCompleted | OnError]Serialized execution of observer’s methods01201120012

Challenge: Simple TransformationImplement Events.LengthChangedImplementObservables.LengthChangedOutput should be:

Bridging from the Existing Worldquery asynchronous data streams

Empty// complete immediatelyObservable.Empty<int>();

Return// return 1 valueObservable.Return(1);1

Throw// throw an exceptionObservable.Throw(newException());

Never// never completeObservable.Never<int>();

Range// return three values starting with 0Observable.Range(0, 3);120

ToEnumerable / ToObservable// enumerable to observableEnumerable.Range(0, 3).ToObservable();// observable to enumerableObservable.Range(0, 3).ToEnumerable();120

Generate// observable for loopObservable.Generate( 0, i => i < 3, i => i + 1, i => i * i);140

Create// anything you pleaseObservable.Create<int>(observer =>{IDisposableb = newBooleanDisposable(); newThread(() => {for (inti = 0; i < 3&& !b.IsDisposed; ++i)observer.OnNext(i);observer.OnCompleted(); return () => {}; }).Start(); returnb;});140

classProgram { static void Main() { Labellbl = newLabel();Formfrm = newForm { Controls = { lbl} };frm.MouseMove+= (s, args) => {}; }}classProgram { static void Main() {Labellbl = newLabel();Formfrm = newForm { Controls = { lbl }};varmouseMoves= Observable.FromEventPattern<MouseEventHandler,MouseEventArgs>( x => frm.MouseMove += x, x => frm.MouseMove -= x);mouseMoves.Subscribe(evt => {}); }}Using Events

classProgram { static void Main() { Labellbl = newLabel();Formfrm = newForm { Controls = { lbl} };frm.MouseMove+= (sender, args) => { if(args.Location.X==args.Location.Y) {lbl.Text =args.Location.ToString(); } };Application.Run(frm); }}classProgram { static void Main() {Labellbl = newLabel();Formfrm = newForm { Controls = { lbl }};varmouseUps = …;varmouseMoves= …;varspecificMoves = fromup inmouseUps frommove inmouseMoves letlocation = move.EventArgs.Location wherelocation.X == location.Y selectnew { location.X, location.Y }; using(specificMoves .Subscribe(evt => lbl.Text= evt.ToString())) {Application.Run(frm); } }}LINQ to Events

ChallengeComplete DictionarySuggestCreate an Observable from the TextChangedevent

Create an Observable from an asynchronous web request

Combine these two observables to react to text input changes to return web service resultsAnswer

Monitoring// anything you pleasevar input = Observable .FromEventPattern(txt, "TextChanged") .Select(evt => ((TextBox)evt.Sender).Text) .Timestamp() .Do((Timestamped<string> evt) => Console.WriteLine(evt)) .Select(evt => evt.Value) .Where(evt => evt.Length > 4) .Do(evt => Console.WriteLine(evt));

ChallengeFind and apply the operators to fix these issues in DictionarySuggest

ChallengePort DictionarySuggest to RxJS

Schedulersparameterizing concurrency

Parameterizing ConcurrencyObservable.Timer(TimeSpan.FromSeconds(5))Which timer?System.Threading.Timer?System.Timers.Timer?System.Windows.Forms.Timer?System.Windows.Threading.Timer?Sleep on the current thread?… ?

Scheduler Abstractionexecution contextclockexecution policy

Scheduler InterfaceinterfaceIScheduler{DateTimeOffset Now { get; }IDisposable Schedule(Action work);IDisposable Schedule(TimeSpandueTime, Action work);IDisposable Schedule(DateTimeOffsetdueTime, Action work);}

Operational LayeringOperatorsvarxs = Observable.Range(1, 10, Scheduler.ThreadPool);var q = from x inxswhere x % 2 == 0select -x;q.Subscribe(Console.WriteLine);

Operational LayeringOperatorsObservablesvarxs = newRangeObservable<int>(1, 10, Scheduler.ThreadPool);var q = newSelectObservable<int>(newWhereObservable<int>(xs, x => x % 2 == 0), x => -x);q.Subscribe( newLambdaObserver<int>(Console.WriteLine));

Operational LayeringOperatorsObservablesvar n = 0;Scheduler.ThreadPool.Schedule(self => {if (n < 10) { if ((n + 1) % 2 == 0)Console.WriteLine(-(n + 1)); n++; self(); }});Schedulers

Operational LayeringOperatorsObservablesvar n = 0;Action<object> work = null;work = _ =>{if (n < 10) { if ((n + 1) % 2 == 0)Console.WriteLine(-(n + 1)); n++;ThreadPool.QueueUserWorkItem(null, work); }};ThreadPool.QueueUserWorkItem(null, work);SchedulersNative Concurrency

One Interface to Rule Them All

The Problem of TimeOperations can take a long timeObservable.Timer(TimeSpan.FromYears(1000))

Some operators have time-based semanticsObservable.Timer(TimeSpan.FromSeconds(1)) .Buffer(TimeSpan.FromSeconds(1))The Problem of Time604512301423561s1s1s1s1s1s1s1s1s1s1s1s1s1s

When testing reactive programs, time is the problem.…virtual time is the solution.The Problem of Time

TestScheduler scheduler = newTestScheduler();IObservable<string> input = scheduler.CreateObservable(OnNext(300, “wes”),OnNext(400, “ryan”),OnCompleted(500));var results = scheduler.Run(() =>input.Select(x => x.Length));results.AssertEqual(OnNext(300, 3),OnNext(400, 4),OnCompleted(500));Unit Testing with Schedulers

Implement MainForm.GetQuotesImplementMainForm.GetQueryChallenge: Historical Data

event processingthe power of LINQ

Given: Stream of stock ticksFind: 10% daily price increaseEvent Processing

WindowingMSFT30.73MSFT27.01MSFT27.96INTC21.75MSFT31.21INTC22.54INTC20.98Group by symbol: GroupBy(t => t.Symbol)

AggregationMSFTINTC30.7327.0127.9631.2121.7522.5420.98Aggregate each day with previous day: Buffer(2, 1)

FilteringMSFTINTC31.2130.7327.0127.9627.9631.2121.7522.5422.5420.98Filter by price increase > 10%: Where(w => PriceIncrease(w) > .1)

ReduceMSFTINTC27.9631.21Reduce to a single stream: Merge()

from tick instockTicksgroup tick bytick.SymbolintosymbolStreamfrom window insymbolStream.Buffer(2, 1)let increase = PriceIncrease(window)where increase > .1select new { symbol = symbolStream.Key, increase }; LINQ: Event Processingsourcegroupaggregateapplyfilterreduce

Change MainForm.Query to compute the Average High and Average Low over the past 5 trading days as well as the current Close and DateChallenge: Event Processing

Reactive coincidencestreaming windows

Representing DurationbeginbeginendendWindow

Reactive CoincidenceWhich people are at the store while it is opened?5/55/6curleymoelarry

Reactive CoincidenceWhich people are at the store while it is opened?5/55/6moelarrycurleymoe

LINQ Joinfrom opening instoreOpeningsjoin person inpersonArrivesonopening.Closeequalsperson.Leavesinto gselectnew { opening.Day, People = g };

Change query in MainForm.MainForm to compute a stream of deltas when the mouse is downChallenge: Drag and Drop

Programming the clouda glimpse into the future

Distributed QueriesCloudresultsquery

Observable.Timer(TimeSpan.FromSeconds(1),Scheduler.Azure) .ObserveLocally() .Subscribe(Console.WriteLine);Distributed QueriesSend the query to the cloudSend the results back

Pass-by-Value [Serializable] classMyType { … }Pass-by-ReferenceclassMyType : MarshalByRefObject{ … }Distributed Parameters

var x = 42;scheduler.Schedule(() =>Console.WriteLine(x));classClosure {public intx;public void M() {Console.WriteLine(x); }}var closure = newClosure();closure.x = 42;scheduler.Schedule(closure.M);Distributed SchedulingPass by value or reference?

interfaceIScheduler { …IDisposable Schedule<T>(T state, Action<T> work); …}Scheduler Interface Revisited

var x = 42;scheduler.Schedule( x, state =>Console.WriteLine(state));static void M(int state) {Console.WriteLine(state);}varx = 42;scheduler.Schedule( x, M);Distributed SchedulingNo closures!!!

scheduler.Schedule(42, x =>scheduler.Schedule(x + 1, y =>Console.WriteLine(y)));Nested Scheduling

Distributed SchedulingcloudScheduler

interfaceIScheduler { …IDisposable Schedule<T>(T state, Action<IScheduler, T> work); …}Scheduler Interface Rerevisited

scheduler.Schedule(42, (s, x) =>s.Schedule(x + 1, y =>Console.WriteLine(y)));Nested Scheduling

Fan-out SchedulingSchedulerSchedulerSchedulerSchedulerSchedulerSchedulerScheduler

var d = scheduler.Schedule(42, (s, x) => {var d1 = s.Schedule(x + 1, Console.WriteLine);var d2 = s.Schedule(x + 2, Console.WriteLine);});Fan-out SchedulingHow do we make d depend on d1 & d2?

interfaceIScheduler { …IDisposable Schedule<T>(T state,Func<IScheduler, T, IDisposable> work); …}Scheduler Interface Rererevisited

var d = scheduler.Schedule(42, (s, x) => {var d1 = s.Schedule(x + 1, Console.WriteLine);vard2 = s.Schedule(x + 2, Console.WriteLine); return newCompositeDisposable(d1, d2);});Fan-out Scheduling

scheduler.Schedule(42, (state, self) => {Console.WriteLine(state); self(state + 1); });Easy Recursive Scheduling

Change Program.Main to use the AppDomainSchedulerReimplementGenerateObservable.SubscribeChallenge: AppDomains

Continuations Everywherecontinuation-passing style used elsewhere

Ruby1..10.each do |x| puts x * xend

AJAX$.ajax({ url: 'http://en.wikipedia.org/w/api.php',dataType: 'jsonp',data: { action: 'opensearch', search: term, format: 'json' },success: function(msg) { alert('Data saved:' + msg);}});

node.jsvar net = require('net');var server = net.createServer(function (socket) {socket.write("Echo server\r\n"); socket.pipe(socket);});server.listen(1337, "127.0.0.1");

ChallengeUsing Rx, build a TCP server that works in a similar manner to node.js.

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