Timur Shemsedinov "Пишу на колбеках, а что... (Асинхронное программирование)"

1. OdessaJS 2017

2. Metarhia

3. Metasync
Library of Asynchronous Programming Abstractions

4. Introduction
Asynchronous programming in JavaScript as of today:
● callbacks
● async.js
● promises
● async/await

5. Callbacks
(...args, callback) => callback(err, data)

6. Library async.js or analogues
async.method(
[...],
(data, callback) => callback(err, result),
(err, result) => {}
);

7. Promise
new Promise((resolve, reject) => {
resolve(data);
reject(new Error());
})
.then(result => {})
.catch(err => {});

8. async/await
async function f() {
return await new Promise(...);
}
f().then(console.log).catch(console.error);

9. Problems
of callbacks, async.js, Promise, async/await
● Nesting
● Different contracts
● Not cancellable, no timeouts
● Complexity and Performance

10. The Concept

12. Metasync
● Function composition for asynchronous I/O
● Specific asynchronous abstractions
● Short and expressive syntax
● We use errback compatible contract
● IH

13. Function composition
inc = a => ++a;
add = (a, b) => (a + b);
lg = x => log(10, x);
f = compose(inc, add, lg);
...but it’s synchronous

14. Function composition
Function composition is a great idea for asynchronous I/O
But there are questions:
● What about contracts?
○ for calls and callbacks, arguments and errors
○ timeouts, queueing, throttling
● How to add asynchronicity?
○ parallel and sequential

15. Asynchronous function composition
const readCfg = (name, cb) => fs.readFile(name, cb);
const netReq = (data, cb) => http.get(data.url, cb);
const dbReq = (query, cb) => db.select(query, cb);
const f1 = sequential(readCfg, netReq, dbReq);
const f2 = parallel(dbReq1, dbReq2, dbReq3);
// f1 & f2 contracts (...args, cb) => cb(err, data)

16. Flow commutation like in electronics
const fx = metasync.flow(
[f1, f2, f3, [[f4, f5, [f6, f7], f8]], f9]
);

17. Data collector
const dc1 = new metasync.DataCollector(4);
const dc2 = new metasync.DataCollector(4, 5000);
dc1.on('error', (err, key) => {});
dc2.on('timeout', (err, data) => {});
dc2.on('done', (errs, data) => {});
dc1.collect(data);

18. Key collector
const keyCollector = new KeyCollector(
['k1', 'k2'], (data) => console.dir(data)
);
keyCollector.collect('k1', {});
fs.readFile('HISTORY.md', (err, data) => {
keyCollector.collect('history', data);
});

19. Key collector
const kc = new metasync.KeyCollector(
['user', 'config', 'readme', 'timer'], (data) => console.dir(data)
);
kc.collect('user', { name: 'Marcus Aurelius' });
fs.readFile('HISTORY.md', (err,data) => kc.collect('history', data));
fs.readFile('README.md', (err,data) => kc.collect('readme', data));
setTimeout(
() => keyCollector.collect('timer', { date: new Date() }),
ASYNC_TIMEOUT
);

20. Collectors
const dc1 = metasync
.collect(3)
.timeout(5000)
.done((err, data) => {});
dc1(item);
const dc2 = metasync
.collect(['key1', 'key2', 'key3'])
.timeout(5000)
.done((err, data) => {});
dc2(key, value);

21. Collector features
const dc = metasync
.collect(count)
.distinct()
.done((err, data) => {});
dc(key, error, value);
dc.pick(key, value);
dc.fail(key, error);
fs.readFile(filename, dc.bind(null, key));
dc.take(key, fs.readFile, filename);

22. Throttle
const t1 = metasync.throttle(5000, f);
t1();
t1();
t1(); // single call
setTimeout(t1, 7000); // another call
setTimeout(t1, 7100);
// will be fired at about 7000+5000

23. Queue
const cq = metasync.queue(3)
.wait(2000)
.timeout(5000)
.throttle(100, 1000)
.process((item, cb) => cb(err, result))
.success((item) => {})
.failure((item) => {})
.done(() => {})
.drain(() => {});

24. Github repo:
https://github.com/metarhia/MetaSync
metarhia.com
tshemsedinov@github
tshemsedinov@facebook
marcusaurelius@habrahabr
timur.shemsedinov@gmail.com

25. Metarhia meetups
meetup.com/KievNodeJS
meetup.com/NodeUA
meetup.com/HowProgrammingWorks

26. Questions

27. Metarhia