semaphore.ts

.gitignore

node_modules
dist

package.json

{
  "devDependencies": {
    "@types/node": "^20.12.7",
    "ts-node": "^10.9.2",
    "typescript": "^5.4.5"
  }
}

semaphore.ts

(Symbol as any).dispose ??= Symbol("Symbol.dispose");
(Symbol as any).asyncDispose ??= Symbol("Symbol.asyncDispose");

class Semaphore {
    private callbacks;

    public constructor(private n: number) {
        this.callbacks = [] as (() => void)[];
    }

    public async acquire() {
        if (this.n <= 0) {
            await new Promise<void>((resolve) => this.callbacks.push(() => resolve()));
        }

        this.n -= 1;

        return {
            [Symbol.dispose]: () => {
                this.n += 1;
                if (this.callbacks.length > 0) {
                    const cb = this.callbacks.shift();
                    cb?.();
                }
            }
        }
    }
}

const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms));
const range = <T,>(n: number, fn: (i: number) => T): T[] => Array.from(new Array(n), (_, i) => fn(i))

const main = async () => {
    const n = 10;
    const m = 30;

    const semaphore = new Semaphore(n);

    const task = async (i: number) => {
        using lock = await semaphore.acquire();

        console.log(`Processing: ${i}`);
        await sleep(1000);
        return i;
    }

    const jobs = await Promise.all(range(m, task));

    console.log(jobs)
}

main()

tsconfig.json

{
  "compilerOptions": {
    "target": "es2022",
    "lib": ["es2022", "ESNext.Disposable"],
    "module": "commonjs",
    "outDir": "./dist",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true
  },
  "include": ["semaphore.ts"]
}

yarn.lock

# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
# yarn lockfile v1


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