How do you implement a custom worker pool with task scheduling?

Question

Accepted Answer

**Worker pool** — manage multiple workers for parallel processing.

```javascript
const { Worker } = require("worker_threads");

class WorkerPool {
    constructor(workerScript, poolSize = 4) {
        this.workerScript = workerScript;
        this.poolSize = poolSize;
        this.workers = [];
        this.queue = [];
        this.init();
    }

init() {
        for (let i = 0; i < this.poolSize; i++) {
            this.createWorker();
        }
    }

createWorker() {
        const worker = new Worker(this.workerScript);
        worker.busy = false;

worker.on("message", (result) => {
            worker.busy = false;
            worker.resolve(result);
            this.processQueue();
        });

worker.on("error", (err) => {
            worker.busy = false;
            worker.reject(err);
            this.processQueue();
        });

this.workers.push(worker);
    }

runTask(data) {
        return new Promise((resolve, reject) => {
            const worker = this.workers.find(w => !w.busy);

if (worker) {
                worker.busy = true;
                worker.resolve = resolve;
                worker.reject = reject;
                worker.postMessage(data);
            } else {
                this.queue.push({ data, resolve, reject });
            }
        });
    }

processQueue() {
        if (this.queue.length === 0) return;

const worker = this.workers.find(w => !w.busy);
        if (!worker) return;

const task = this.queue.shift();
        worker.busy = true;
        worker.resolve = task.resolve;
        worker.reject = task.reject;
        worker.postMessage(task.data);
    }

async destroy() {
        for (const worker of this.workers) {
            await worker.terminate();
        }
    }
}

// Usage
const pool = new WorkerPool("./heavy-task.js", 4);
const results = await Promise.all([
    pool.runTask({ input: 1 }),
    pool.runTask({ input: 2 }),
    pool.runTask({ input: 3 }),
    pool.runTask({ input: 4 }),
]);
```

Node.js: How do you implement a custom worker pool with task scheduling?