a general theory of reactivity
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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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
• 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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
ARRAY-RETURNING FUNCTION
function range(start, stop, step) { var result = []; while (start < stop) { result.push(start); start += step; } return result;}
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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
PROMISE IN A NUTSHELL
out = in.then( inval => outres, inerr => outres );
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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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)
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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
A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
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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A GENERAL THEORY OF REACTIVITY (GTOR) KRIS KOWAL
MARCH 1, 2015
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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