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6-counting-safe.js
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56 lines (49 loc) · 1.44 KB
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'use strict';
const fs = require('node:fs');
const threads = require('node:worker_threads');
const { Worker, isMainThread } = threads;
class CountingSemaphore {
constructor(shared, offset = 0, initial) {
this.counter = new Int32Array(shared, offset, 1);
if (typeof initial === 'number') {
Atomics.store(this.counter, 0, initial);
}
}
enter() {
while (true) {
Atomics.wait(this.counter, 0, 0);
const n = Atomics.load(this.counter, 0);
if (n > 0) {
const prev = Atomics.compareExchange(this.counter, 0, n, n - 1);
if (prev === n) return;
}
}
}
leave() {
Atomics.add(this.counter, 0, 1);
Atomics.notify(this.counter, 0, 1);
}
}
// Usage
if (isMainThread) {
const buffer = new SharedArrayBuffer(4);
// Try to change 10 to 2 at next line to check solution
const semaphore = new CountingSemaphore(buffer, 0, 10);
console.dir({ semaphore: semaphore.counter[0] });
for (let i = 0; i < 20; i++) {
new Worker(__filename, { workerData: buffer });
}
} else {
const { threadId, workerData } = threads;
const semaphore = new CountingSemaphore(workerData);
const REPEAT_COUNT = 1000000;
const file = `file-${threadId}.dat`;
console.dir({ threadId, semaphore: semaphore.counter[0] });
semaphore.enter();
const data = `Data from ${threadId}`.repeat(REPEAT_COUNT);
fs.writeFile(file, data, () => {
fs.unlink(file, () => {
semaphore.leave();
});
});
}