A General Theory of Reactivity

A GENERAL THEORY OF REACTIVITYKRIS KOWAL [email protected] @KRISKOWAL

mailto:[email protected]

Troy McClure — The Simpsons

A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL

MARCH 1, 2015

A GENERAL THEORY OF RELATIVITY

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Albert Einstein in 1921, as he rode in a motorcade in New York City with crowds welcoming his first visit to the U.S., Life Magazine, Public Domain


MARCH 1, 2015

• sync / async • singular / plural • single consumer / multiple consumers • unicast (cancelable) / broadcast • coping with fast producer | slow consumer

DIMENSIONS OF REACTIVITY

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• push → discrete over time, observables, gauges, drop messages

• pull ← continuous over time, behaviors, counters, lose fidelity

• pressure ↔ reliable, streams

FAST PRODUCER | SLOW CONSUMER

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MARCH 1, 2015

STREAMS ARE LIKE ARRAYS (PLURAL) PROMISES (ASYNC)

return Stream.from(fileNames).map(fileName => fs.readFile(fileName).then(content => ({fileName, content}) }, null, 20).forEach(({fileName, content}) => console.log(fileName, content.length));

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value

getter setter

singular

synchronous

Duality — a là Erik Meijer

value (getter and setter)

get(Void):Value

set(Value):Void

info

rmat

ion

space

singular plural

sync

collection

iterator generator

value

getter setter

iterator (pull, sync)

next():{done:Boolean, value:Value}

info

rmat

ion

generator (push, sync)

{next(Value), return(Value), throw(Error)}

info

rmat

ion

generator and observer (push, sync)

{observe(onNext(Value), onReturn(Value), onThrow(Error))}

{next(Value), return(Value), throw(Error)}

info

rmat

ion


MARCH 1, 2015

PUSH •Use Observer

•For discrete time series data

•changes in response to an event

•e.g., estimated time to completion

•(02:30)

•Rx, a là Erik Meijer

PUSH VS PULL FOR TIME SERIES VALUES

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PULL • Use Iterator

• For continuous time series data

• always changing, must be sampled periodically

• e.g., progress to completion

• (50%)

• FRP, a là Conal Elliott

generator function (pull, sync)

next(Void):Iteration<Value>

yield Value / return Value / throw Error

info

rmat

ion


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ARRAY-RETURNING FUNCTION

function range(start, stop, step) { var result = []; while (start < stop) { result.push(start); start += step; } return result;}

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GENERATOR FUNCTION

function* range(start, stop, step) {

while (start < stop) {

yield start;

start += step;

} }

var iterator = range(0, 4, 2);

iterator.next(); // {done: false, value: 0}

iterator.next(); // {done: false, value: 2}

iterator.next(); // {done: true, value: undefined}

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space

time

sync

async

singular plural

collection

iterator generator

value

getter setter

deferred

promise resolver

deferred (pomise and resolver)

{then(onReturn(Value), onThrow(Error))}

{return(Value | Promise<Value>), throw(Error)}

info

rmat

ion


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PROMISE IN A NUTSHELL

out = in.then( inval => outres, inerr => outres );

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PLAN INTERFERENCE

var i = 0; yolo(function lol() { i++; }); console.log(i);

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time

then(onReturn)

resolve(value)

time

resolve(value)

then(onReturn)

promises and order independence

onReturn(value)


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ASYNC FUNCTION

function time(job) { let start = Date.now(); return job().then( () => Date.now() - start ); } async function sum(getX, getY) { return await getX() + await getY(); } sum(time(task), time(task)).then(console.log);

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PROMISES

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•order independence

•guaranteed async (zalgo containment)

•defensive

•POLA (one-way communication)

•chainability

•composability

•gateway to proxies for remote objects

•a là Mark Miller

space

time

sync

async

singular plural

collection

iterator generator

value

getter setter

stream

reader writer

deferred

promise resolver

promise queue

get() Promise<Value>

put(Value | Promise<Value>)

info

rmat

ion

order

put

order

promise queues and order independence

put

producer

consumer

put

get getget

promise queue to transport iterations

get() Promise<{value: Value, done: Boolean}>

put({value: Value, done: Boolean})

info

rmat

ion


MARCH 1, 2015

LINKED LIST MEETS TEMPORAL RIFT

PROMISE QUEUE IMPLEMENTATION

function AsyncQueue() { var ends = Promise.defer(); this.put = function (value) { var next = Promise.defer(); ends.resolver.return({head: value, tail: next.promise}); ends.resolver = next.resolver; }; this.get = function () { var result = ends.promise.get("head"); ends.promise = ends.promise.get("tail"); return result; }; }

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reader.next() -> promise

writer.next(value) -> promise

promise queuesput

get put

get

buffer (async, plural, push and pull)

{next(Value) -> Promise<Iteration<Value>>, return(Value), throw(Error)}

bid

irec

tional


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ASYNC GENERATOR FUNCTION

async function* sumPairwise(stream) { while (true) let x = await stream.next(); if (x.done) return x.value; let y = await stream.next(); if (y.done) return y.value; yield x.value + y.value; } }

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space

time

sync

async

singular plural

collection

iterator generator

value

getter setter

stream

reader writer

deferred

promise resolver


MARCH 1, 2015

SHARE A STREAM

var source = Stream.from(Iterator.range(100)) .map((n) => Task.delay(250).thenReturn(n))

Iterator.range(3).forEach((delay) => return source.map( (n) => Task.delay(delay * 1000).thenReturn(n); ); );

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MARCH 1, 2015

FORK A STREAM

var branches = Stream.from(Iterator.range(100)) .map((n) => Task.delay(250).thenReturn(n)) .fork(3); branches.forEach( (branch) => branch.forEach( (n) => Task.delay(1000 + Math.random() * 1000) .thenReturn(n) ).done() );

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MARCH 1, 2015

MAP A STREAM WITH A CONCURRENCY LIMIT

var branches = Stream.from(Iterator.range(100)) .map((n) => Task.delay(random()).thenReturn(n), null, 32) .map((n) => Task.delay(random()).thenReturn(n), null, 16) .map((n) => Task.delay(random()).thenReturn(n), null, 4) .map((n) => Task.delay(random()).thenReturn(n), null, 1) .forEach((n) => null).done()

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MARCH 1, 2015

REDUCE A STREAM TO FIND THE MAX

return Stream.from(source).reduce((max, value) => Task.delay(500 + 500 * Math.random()) .thenReturn(Math.max(max, value)) ).then((max) => { console.log(max);})

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MAP | REDUCE

return Stream.from(source).map( (value) => Task.delay(random()) .thenReturn(value), null, 32 ).reduce( (max, value) => Task.delay(random()) .thenReturn(Math.max(max, value)), null, 32 );

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GTORKRIS KOWAL [email protected] @KRISKOWAL

mailto:[email protected]

Documents

A General Theory of Reactivity