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How are Race Conditions in single threaded JavaScript possible?

Timur Shemsedinov
Timur Shemsedinov

Race conditions in single-threaded JavaScript are possible due to asynchronous code execution using callbacks, promises, and async/await. Common concurrency problems include race conditions, deadlocks, and resource starvation. Potential solutions include synchronization primitives like mutexes and semaphores, resource locking, and flow commutation to control the order of asynchronous operations.

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const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c toString().padStart(width) : cell.padEnd(width); }).join(''))).join }; const proportion = (max, val) => Math.round(val * 100 / max); co calcProportion = table => { table.sort((row1, row2) => row2[DENSITY row1[DENSITY_COL]); const maxDensity = table[0][DENSITY_COL]; table forEach(row => { row.push(proportion(maxDensity, row[DENSITY_COL])) return table; }; const getDataset = file => { const lines = fs.read FileSync(file, 'utf8').toString().split('n'); lines.shift(); lines return lines.map(line => line.split(',')); }; const main = compose (getDataset, calcProportion, renderTable); const fs = require('fs' compose = (...funcs) => x => funcs.reduce((x, fn) => fn(x), x); con DENSITY_COL = 3; const renderTable = table => { const cellWidth = [ 8, 8, 18, 6]; return table.map(row => (row.map((cell, i) => { const = cellWidth[i]; return i ? cell.toString().padStart(width) : cell.p (width); }).join(''))).join('n'); }; const proportion = (max, val) How are Race Conditions in single threaded JS possible? Timur Shemsedinov github.com/tshemsedinov Chief Software Architect at Metarhia Lecturer at Kiev Polytechnic Institute
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Concurrency Problems ● Race condition ● Deadlock ● Livelock ● Resource starvation ● Resource leaks
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions javascruptissinglethreaded
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions nodejsissinglethreaded
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions Promises async/await
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Concurrent Computing
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition class Point { constructor(x, y) { this.x = x; this.y = y; } async move(dx, dy) { this.x = await add(this.x, dx); this.y = await add(this.y, dy); } }
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition const random = (min, max) => Math .floor(Math.random() * (max - min + 1)) + min; const add = (x, dx) => new Promise(resolve => { setTimeout(() => { resolve(x + dx); }, random(20, 100)); });
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition const p1 = new Point(10, 10); console.log(p1); p1.move(5, 5); p1.move(6, 6); p1.move(7, 7); p1.move(8, 8); setTimeout(() => { console.log(p1); }, 1000);
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition Initial Point { x: 10, y: 10 } Expected Point { x: 36, y: 36 } Actual Point { x: 18, y: 25 }
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Possible Solutions ● Synchronization ● Resource locking ● Special control flow organization ● Queuing theory ● Actor model ● Use DBMS transactions
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Synchronization Primitives Semaphore Binary semaphore Counting semaphore Condition variable Spinlock Mutex Timed mutex Shared mutex Recursive mutex Monitor Barrier
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Semaphore class Semaphore { constructor() enter(callback) leave() } semaphore.enter(() => { // do something semaphore.leave(); }); github.com/HowProgrammingWorks/Semaphore class Semaphore { constructor() async enter() leave() } await semaphore.enter(); // do something semaphore.leave();
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Mutex class Mutex { constructor() async enter() leave() } await mutex.enter(); // do something with shared resources mutex.leave(); https://github.com/HowProgrammingWorks/Mutex
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking class Lock { constructor() { this.active = false; this.queue = []; } leave() { if (!this.active) return; this.active = false; const next = this.queue.pop(); if (next) next(); } } enter() { return new Promise(resolve => { const start = () => { this.active = true; resolve(); }; if (!this.active) { start(); return; } this.queue.push(start); }); }
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking class Point { constructor(x, y) { this.x = x; this.y = y; this.lock = new Lock(); } async move(dx, dy) { await this.lock.enter(); this.x = await add(this.x, dx); this.y = await add(this.y, dy); this.lock.leave(); } }
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking const p1 = new Point(10, 10); console.log(p1); p1.move(5, 5); p1.move(6, 6); p1.move(7, 7); p1.move(8, 8); setTimeout(() => { console.log(p1); }, 1000);
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking Initial Point { x: 10, y: 10 } Expected Point { x: 36, y: 36 } Actual Point { x: 36, y: 36 }
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Asynchronous Res Locks
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Flow Commutation const fx = metasync( [f1, f2, f3, [[f4, f5, [f6, f7], f8]], f9] ); like in electronics
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Real-life Example Warehouse API ● Check balances ● Ship goods ● Lock balances github.com/HowProgrammingWorks/RaceCondition
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks API locks.request('resource', opt, async lock => { if (lock) { // critical section for `resource` // will be released after return } }); https://wicg.github.io/web-locks/
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: await (async () => { await something(); await locks.request('resource', async lock => { // critical section for `resource` }); await somethingElse(); })();
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Promise locks.request('resource', lock => new Promise( (resolve, reject) => { // you can store or pass // resolve and reject here } ));
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Thenable locks.request('resource', lock => ({ then((resolve, reject) => { // critical section for `resource` // you can call resolve and reject here }) }));
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Abort 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 });
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks for Node.js github.com/nodejs/node/issues/22702 Open github.com/nodejs/node/pull/22719 Closed
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Safe data structures ● Low-level structures e.g. Register, Counter, Buffer, Array, Lists, etc. ● Abstract structures e.g. Queue, Graph, Polyline, etc. ● Subject-domain classes e.g. Sensors, Payment, Biometric data, etc. ● Resources and handles e.g. Sockets, Connections, Streams, etc.
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Deadlock (async () => { await locks.request('A', async lock => { await locks.request('B', async lock => { }); }); })(); (async () => { await locks.request('B', async lock => { await locks.request('A', async lock => { }); }); })();
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Livelock State1 State2 State3 State4
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Alternative Solutions ● Thread safe data structures ● Lock-free data structures ● Wait-free algorithms ● Conflict-free data structures
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Links habr.com/ru/post/452974/ github.com/HowProgrammingWorks/RaceCondition github.com/HowProgrammingWorks/Semaphore github.com/HowProgrammingWorks/Mutex github.com/metarhia/metasync wicg.github.io/web-locks
const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Thanks github.com/tshemsedinov youtube.com/TimurShemsedinov github.com/HowProgrammingWorks timur.shemsedinov@gmail.com

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How are Race Conditions in single threaded JavaScript possible?

  • 1. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c toString().padStart(width) : cell.padEnd(width); }).join(''))).join }; const proportion = (max, val) => Math.round(val * 100 / max); co calcProportion = table => { table.sort((row1, row2) => row2[DENSITY row1[DENSITY_COL]); const maxDensity = table[0][DENSITY_COL]; table forEach(row => { row.push(proportion(maxDensity, row[DENSITY_COL])) return table; }; const getDataset = file => { const lines = fs.read FileSync(file, 'utf8').toString().split('n'); lines.shift(); lines return lines.map(line => line.split(',')); }; const main = compose (getDataset, calcProportion, renderTable); const fs = require('fs' compose = (...funcs) => x => funcs.reduce((x, fn) => fn(x), x); con DENSITY_COL = 3; const renderTable = table => { const cellWidth = [ 8, 8, 18, 6]; return table.map(row => (row.map((cell, i) => { const = cellWidth[i]; return i ? cell.toString().padStart(width) : cell.p (width); }).join(''))).join('n'); }; const proportion = (max, val) How are Race Conditions in single threaded JS possible? Timur Shemsedinov github.com/tshemsedinov Chief Software Architect at Metarhia Lecturer at Kiev Polytechnic Institute
  • 2. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Concurrency Problems ● Race condition ● Deadlock ● Livelock ● Resource starvation ● Resource leaks
  • 3. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions javascruptissinglethreaded
  • 4. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions nodejsissinglethreaded
  • 5. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Solutions Promises async/await
  • 6. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Concurrent Computing
  • 7. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition class Point { constructor(x, y) { this.x = x; this.y = y; } async move(dx, dy) { this.x = await add(this.x, dx); this.y = await add(this.y, dy); } }
  • 8. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition const random = (min, max) => Math .floor(Math.random() * (max - min + 1)) + min; const add = (x, dx) => new Promise(resolve => { setTimeout(() => { resolve(x + dx); }, random(20, 100)); });
  • 9. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition const p1 = new Point(10, 10); console.log(p1); p1.move(5, 5); p1.move(6, 6); p1.move(7, 7); p1.move(8, 8); setTimeout(() => { console.log(p1); }, 1000);
  • 10. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition Initial Point { x: 10, y: 10 } Expected Point { x: 36, y: 36 } Actual Point { x: 18, y: 25 }
  • 11. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Race Condition
  • 12. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Possible Solutions ● Synchronization ● Resource locking ● Special control flow organization ● Queuing theory ● Actor model ● Use DBMS transactions
  • 13. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Synchronization Primitives Semaphore Binary semaphore Counting semaphore Condition variable Spinlock Mutex Timed mutex Shared mutex Recursive mutex Monitor Barrier
  • 14. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Semaphore class Semaphore { constructor() enter(callback) leave() } semaphore.enter(() => { // do something semaphore.leave(); }); github.com/HowProgrammingWorks/Semaphore class Semaphore { constructor() async enter() leave() } await semaphore.enter(); // do something semaphore.leave();
  • 15. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Mutex class Mutex { constructor() async enter() leave() } await mutex.enter(); // do something with shared resources mutex.leave(); https://github.com/HowProgrammingWorks/Mutex
  • 16. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking class Lock { constructor() { this.active = false; this.queue = []; } leave() { if (!this.active) return; this.active = false; const next = this.queue.pop(); if (next) next(); } } enter() { return new Promise(resolve => { const start = () => { this.active = true; resolve(); }; if (!this.active) { start(); return; } this.queue.push(start); }); }
  • 17. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking class Point { constructor(x, y) { this.x = x; this.y = y; this.lock = new Lock(); } async move(dx, dy) { await this.lock.enter(); this.x = await add(this.x, dx); this.y = await add(this.y, dy); this.lock.leave(); } }
  • 18. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking const p1 = new Point(10, 10); console.log(p1); p1.move(5, 5); p1.move(6, 6); p1.move(7, 7); p1.move(8, 8); setTimeout(() => { console.log(p1); }, 1000);
  • 19. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking Initial Point { x: 10, y: 10 } Expected Point { x: 36, y: 36 } Actual Point { x: 36, y: 36 }
  • 20. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Resource Locking
  • 21. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Asynchronous Res Locks
  • 22. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Flow Commutation const fx = metasync( [f1, f2, f3, [[f4, f5, [f6, f7], f8]], f9] ); like in electronics
  • 23. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Real-life Example Warehouse API ● Check balances ● Ship goods ● Lock balances github.com/HowProgrammingWorks/RaceCondition
  • 24. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks API locks.request('resource', opt, async lock => { if (lock) { // critical section for `resource` // will be released after return } }); https://wicg.github.io/web-locks/
  • 25. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: await (async () => { await something(); await locks.request('resource', async lock => { // critical section for `resource` }); await somethingElse(); })();
  • 26. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Promise locks.request('resource', lock => new Promise( (resolve, reject) => { // you can store or pass // resolve and reject here } ));
  • 27. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Thenable locks.request('resource', lock => ({ then((resolve, reject) => { // critical section for `resource` // you can call resolve and reject here }) }));
  • 28. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks: Abort 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 });
  • 29. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Web Locks for Node.js github.com/nodejs/node/issues/22702 Open github.com/nodejs/node/pull/22719 Closed
  • 30. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Safe data structures ● Low-level structures e.g. Register, Counter, Buffer, Array, Lists, etc. ● Abstract structures e.g. Queue, Graph, Polyline, etc. ● Subject-domain classes e.g. Sensors, Payment, Biometric data, etc. ● Resources and handles e.g. Sockets, Connections, Streams, etc.
  • 31. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Deadlock (async () => { await locks.request('A', async lock => { await locks.request('B', async lock => { }); }); })(); (async () => { await locks.request('B', async lock => { await locks.request('A', async lock => { }); }); })();
  • 32. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Livelock State1 State2 State3 State4
  • 33. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Alternative Solutions ● Thread safe data structures ● Lock-free data structures ● Wait-free algorithms ● Conflict-free data structures
  • 34. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Links habr.com/ru/post/452974/ github.com/HowProgrammingWorks/RaceCondition github.com/HowProgrammingWorks/Semaphore github.com/HowProgrammingWorks/Mutex github.com/metarhia/metasync wicg.github.io/web-locks
  • 35. const fs = require('fs'); const compose = (...funcs) => x => funcs. reduce((x, fn) => fn(x), x); const DENSITY_COL = 3; const renderTab table => { const cellWidth = [18, 10, 8, 8, 18, 6]; return table.ma => (row.map((cell, i) => { const width = cellWidth[i]; return i ? c Thanks github.com/tshemsedinov youtube.com/TimurShemsedinov github.com/HowProgrammingWorks [email protected]