Совсем недавно worker_threads появился в Node.js, а вместе с SharedArrayBuffer и Atomics стало возможным создавать многопоточные приложения с разделяемой памятью, а значит в Node.js теперь возможно не только асинхронное, но и параллельное программирование с его абстракциями: критические секции, состояние гонки, дедлоки и лайвлоки, блокировки и синхронизация, семафоры и счетчики, мьютексы, мониторы и прочие проблемы и решения, накопленные в многопоточных языках. Я дам обзор с примерами кода, а так же кейсы применения worker_threads в Node.js и практическая польза от этого. Так же, краткий перечень еще не решенных проблем с воркерами, возможно, кого-то это заинтересует начать контрибьютить в Node.js.

1. Timur Shemsedinov
PROFESSIONAL JS CONFERENCE 5-6 APRIL ‘19 KIEV, UKRAINE
Introduction to multithreading concurrent programming in
Node.js with worker_threads, SharedArrayBuffer and Atomics
Shared memory and
multithreading in Node.js

2. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Process
- Separate memory
- Separate resources
- Separate environment
Process / Thread
Thread
- Shared memory space
- Shared resources
- Common environment
Memory mapped files

3. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js
- child_process
- cluster
- worker_threads
--experimental-worker
- Atomics
- SharedArrayBuffer
Node.js 10.5 ... 11.7

4. process
PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
process
JavaScript
thread
V8 libuv
node.js
JavaScript
Shared memory and Message passing
thread
V8 libuv
node.js
JavaScript
thread
V8 libuv
node.js
IPC

5. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js: worker_threads
Not supported:
- process.abort()
- process.chdir(name)
- process.initgroups(...)
- trace_events module
- IPC from parent
- process.setegid(id)
- process.seteuid(id)
- process.setgid(id)
- process.setgroups(...)
- process.setuid(id)

6. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js: worker_threads
Read-only in Worker threads:
- process.env
- process.title
- process.umask([mask])

7. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js: worker_threads
Different behavior:
- process.exit([code]) stops thread not process
- process.memoryUsage() rss for entire process
- Each thread has an independent async_hooks
- Signals will not be delivered through process.on

8. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js: worker_threads API
const threads = require('worker_threads');
const { Worker, isMainThread } = threads;
if (isMainThread) {
const worker =
new Worker(__filename, { workerData: {} });
} else {
const { parentPort } = threads;
}

9. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Node.js: MessagePort API
worker.on('message', (...args) => {});
worker.on('error', err => {});
worker.on('exit', code => {});
worker.postMessage('Hello there!');
parentPort.postMessage('Hello there!');
parentPort.on('message', (...args) => {});

10. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
class Point {
constructor(buffer, offset) {
this.data = new Int8Array(buffer, offset, 2);
}
get x() { return this.data[0]; }
set x(value) { this.data[0] = value; }
...
Wrap Shared Memory with OOP

11. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
const buffer = new SharedArrayBuffer(64);
const point = new Point(buffer, 4);
point.x += 10;
point.y = 7;
const { x } = point;
Wrap Shared Memory with OOP

12. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- Parallel Programming
- Asynchronous Programming
- Actor Model
- Transactional Memory
- Coroutines
Concurrent Computing

13. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Parallel Programming
- Race condition
- Critical section
- Deadlock
- Livelock
- Starvation

14. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Int8Array, Uint8Array,
Int16Array, Uint16Array,
Int32Array, Uint32Array
Atomics and SharedArrayBuffer

15. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
prev = Atomics.add(array, index, value)
prev = Atomics.sub(array, index, value)
prev = Atomics.and(array, index, value)
prev = Atomics.or(array, index, value)
prev = Atomics.xor(array, index, value)
ES2017 Atomics

16. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
function add(array, index, value) {
1 const prev = array[index];
2 const sum = prev + value;
3 array[index] = sum;
4 return prev;
}
Atomics.add(array, index, value)

17. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
stored = Atomics.store(array, index, value)
value = Atomics.load(array, index)
prev = Atomics.exchange(array, index, value)
prev = Atomics.compareExchange(
array, index, expected, replacement
)
ES2017 Atomics (CAS)

18. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
woken = Atomics.notify(array, index, count)
res = Atomics.wait(array, index, value, [timeout])
res <"ok" | "not-equal" | "timed-out">
array <Int32Array>
ES2017 Atomics (notify/wait)

19. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
Synchronization primitives
- Semaphore
- BinarySemaphore
- CountingSemaphore
- Condition variable
- SpinLock
- Mutex
- TimedMutex
- SharedMutex
- RecursiveMutex
- Monitor
- Barrier

20. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- thread safe data structures
- lock-free data structures
- wait-free algorithms
- conflict-free data structures
Parallel Solutions

21. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
class Mutex {
constructor(shared, offset = 0)
enter()
leave()
}
https://github.com/HowProgrammingWorks/Mutex
Mutex

22. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
mutex.enter();
// do something
// with shared resources
// or data structures
mutex.leave();
Mutex usage

23. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
constructor(shared, offset = 0) {
this.lock = new Int32Array(shared, offset, 1);
this.owner = false;
}
const threads = require('worker_threads');
const { workerData } = threads;
const mutex1 = new Mutex(workerData, offset);
Mutex constructor

24. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
enter() {
let prev = Atomics.exchange(this.lock, 0, LOCKED);
while (prev !== UNLOCKED) {
Atomics.wait(this.lock, 0, LOCKED);
prev = Atomics.exchange(this.lock, 0, LOCKED);
}
this.owner = true;
} Example: 6-blocking.js
Mutex.enter with Atomics.wait

25. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
leave() {
if (!this.owner) return;
Atomics.store(this.lock, 0, UNLOCKED);
Atomics.notify(this.lock, 0, 1);
this.owner = false;
}
Mutex.leave with Atomics.notify

26. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
mutex.enter(() => {
// do something
// with shared resources
// or data structures
mutex.leave();
});
Async Mutex usage

27. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
await mutex.enter();
// do something
// with shared resources
// or data structures
mutex.leave();
Async Mutex usage

28. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
enter() {
return new Promise(resolve => {
while (true) {
let prev = Atomics.exchange(this.lock, 0, LOCKED);
if (prev === UNLOCKED) break;
}
this.owner = true;
resolve();
});
}
Spinlock

29. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
enter() {
return new Promise(resolve => {
const tryEnter = () => {
let prev = Atomics.exchange(this.lock, 0, LOCKED);
if (prev === UNLOCKED) {
this.owner = true;
resolve();
} else {
setTimeout(tryEnter, 0);
}
};
tryEnter();
});
}
Spinlock with setTimeout

30. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
constructor(messagePort, shared, offset = 0) {
this.port = messagePort;
this.lock = new Int32Array(shared, offset, 1);
this.owner = false;
this.trying = false;
this.resolve = null;
if (messagePort) {
messagePort.on('message', kind => {
if (kind === 'leave' && this.trying) this.tryEnter();
});
} Example: 8-async.js
}
Asynchronous Mutex

31. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
enter() {
return new Promise(resolve => {
this.resolve = resolve;
this.trying = true;
this.tryEnter();
});
}
Asynchronous Mutex.enter

32. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
tryEnter() {
if (!this.resolve) return;
let prev = Atomics.exchange(this.lock, 0, LOCKED);
if (prev === UNLOCKED) {
this.owner = true;
this.trying = false;
this.resolve();
this.resolve = null;
}
}
Asynchronous Mutex.tryEnter

33. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- Low-level structures
e.g. Register, Counter, Buffer, Array, Lists...
- Abstract structures
e.g. Queue, Graph, Polyline, etc.
- Subject-domain classes
e.g. Sensors, Payment, Biometric data, etc.
Thread safe data structures

34. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
locks.request('resource', opt, async lock => {
if (lock) {
// critical section for `resource`
// will be released after return
}
});
https://wicg.github.io/web-locks/
Web Locks API

35. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- https://github.com/nodejs/node/issues/22702
Open
- https://github.com/nodejs/node/pull/22719
Closed
Web Locks for Node.js

36. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- Web Locks requires memory + messaging
- Multiple locks.request() calls requires queue
- Mutex.queue: Array<Lock> // resource
- Lock { name, mode, callback } // request
- Need await locks.request()
- Options: { mode, ifAvailable, steal, signal }
Web Locks API Implementation

37. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
locks.request('resource', lock => new Promise(
(resolve, reject) => {
// you can store or pass resolve and
// reject here as callbacks
}
));
https://wicg.github.io/web-locks/
Web Locks: Promise or thenable

38. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
const controller = new AbortController();
setTimeout(() => controller.abort(), 200);
const { signal } = controller;
locks.request('resource', { signal }, async lock => {
// lock is held
}).catch(err => {
// err is AbortError
});
Web Locks: Abort

39. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
- Passing handles between workers
- Native add-ons (with certain conditions)
- Debug
- Experimental
https://github.com/nodejs/node/issues/22940
To be solved

40. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
https://github.com/HowProgrammingWorks/Semaphore
https://github.com/HowProgrammingWorks/Mutex
https://github.com/metarhia/metasync
https://wicg.github.io/web-locks
https://nodejs.org/api/worker_threads.html
https://developer.mozilla.org/en-US/docs/Web/
JavaScript/Reference/Global_Objects/Atomics
Links

41. PROFESSIONAL JS CONFERENCE Shared memory and multithreading in Node.js
https://github.com/tshemsedinov
https://www.youtube.com/TimurShemsedinov
timur.shemsedinov@gmail.com
Thanks