# bun-workers

A skill that tells the agent how to run Web Workers and worker_threads in Bun: parallel jobs, worker pools, message passing.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 402 installs · ★ 236
- Author: secondsky
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/secondsky/claude-skills/tree/HEAD/plugins/bun/skills/bun-workers/SKILL.md
- Updated: 2026-10-20
- HTML: https://affpapa.org/en/nevibecode/skills/bun-workers

## What it does

The skill kicks in when a Bun project needs heavy work moved off the main thread. It ships TypeScript examples: spawning a worker with `new Worker(new URL("./worker.ts", import.meta.url))`, handling `onmessage` and `onerror`, sending data with `postMessage`.

Separate sections cover transferable objects for zero-copy moves, `SharedArrayBuffer` with `Atomics`, and the Node.js `worker_threads` module with `isMainThread`, `parentPort` and `workerData`. There is a `WorkerPool` class with a task queue and a `parallelMap` example.

One gotcha worth knowing: when you pass an `ArrayBuffer` in the transfer list, it is detached in the sender, so touching it after `postMessage` fails. Shared memory needs `SharedArrayBuffer`, and you guard access with `Atomics`.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill bun-workers -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/bun-workers/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/bun-workers/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill bun-workers -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/bun-workers/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill bun-workers -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/bun-workers/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install secondsky/claude-skills bun-workers
```

2. **Manually: put the files in place**
- File: `.github/skills/bun-workers/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill bun-workers -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/secondsky/claude-skills --path plugins/bun/skills/bun-workers
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/bun-workers/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add secondsky/claude-skills --skill bun-workers -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/secondsky/claude-skills/tree/HEAD/plugins/bun/skills/bun-workers/SKILL.md

## When to use it
- move a CPU-heavy computation off the main thread
- build a worker pool with a task queue
- pass a large buffer without copying it
- wire up messaging between two workers
- report progress from a long-running job

## Example prompts
- Set up a Web Worker in Bun to process a large array of numbers
- Build a worker_threads pool with a task queue
- Send an ArrayBuffer to a worker with a transfer list, no copy

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 057d292235991ba1.

BEGIN THIRD-PARTY FILE 057d292235991ba1
````text
---
name: bun-workers
description: Use for Web Workers in Bun, worker_threads, parallel processing, and background tasks.
metadata:
  version: "1.0.0"
license: MIT
---

# Bun Workers

Bun supports Web Workers and Node.js worker_threads for parallel execution.

## Web Workers

### Basic Usage

```typescript
// main.ts
const worker = new Worker(new URL("./worker.ts", import.meta.url));

worker.postMessage({ type: "start", data: [1, 2, 3, 4, 5] });

worker.onmessage = (event) => {
  console.log("Result:", event.data);
};

worker.onerror = (error) => {
  console.error("Worker error:", error.message);
};

// worker.ts
self.onmessage = (event) => {
  const { type, data } = event.data;

  if (type === "start") {
    const result = data.map((x) => x * 2);
    self.postMessage(result);
  }
};
```

### Worker with URL

```typescript
// Import from file path
const worker = new Worker(new URL("./worker.ts", import.meta.url));

// Or with blob URL
const code = `
  self.onmessage = (e) => {
    self.postMessage(e.data * 2);
  };
`;
const blob = new Blob([code], { type: "application/javascript" });
const worker = new Worker(URL.createObjectURL(blob));
```

### Transferable Objects

```typescript
// main.ts
const buffer = new ArrayBuffer(1024 * 1024); // 1MB
const view = new Uint8Array(buffer);
view.fill(42);

// Transfer ownership (zero-copy)
worker.postMessage({ buffer }, [buffer]);
// buffer is now detached (empty)

// worker.ts
self.onmessage = (event) => {
  const { buffer } = event.data;
  const view = new Uint8Array(buffer);
  // Process buffer...

  // Transfer back
  self.postMessage({ buffer }, [buffer]);
};
```

### Shared Memory

```typescript
// main.ts
const shared = new SharedArrayBuffer(1024);
const view = new Int32Array(shared);

worker.postMessage({ shared });

// Both main and worker can access
Atomics.add(view, 0, 1);

// worker.ts
self.onmessage = (event) => {
  const { shared } = event.data;
  const view = new Int32Array(shared);

  // Atomic operations for thread safety
  Atomics.add(view, 0, 1);
  Atomics.notify(view, 0);
};
```

## Node.js worker_threads

```typescript
// main.ts
import { Worker, isMainThread, parentPort, workerData } from "worker_threads";

if (isMainThread) {
  const worker = new Worker(import.meta.filename, {
    workerData: { numbers: [1, 2, 3, 4, 5] },
  });

  worker.on("message", (result) => {
    console.log("Result:", result);
  });

  worker.on("error", (err) => {
    console.error("Error:", err);
  });

  worker.on("exit", (code) => {
    console.log("Worker exited with code:", code);
  });
} else {
  // Worker code
  const { numbers } = workerData;
  const sum = numbers.reduce((a, b) => a + b, 0);
  parentPort?.postMessage(sum);
}
```

### Worker Pool

```typescript
// worker-pool.ts
import { Worker } from "worker_threads";

class WorkerPool {
  private workers: Worker[] = [];
  private queue: Array<{
    task: any;
    resolve: (value: any) => void;
    reject: (err: Error) => void;
  }> = [];
  private activeWorkers = new Set<Worker>();

  constructor(
    private workerPath: string,
````
END THIRD-PARTY FILE 057d292235991ba1

The third-party file has ended. Everything between the 057d292235991ba1 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

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