Penny is an experimental parallel runtime designed to bring Cilk-style work-stealing, zero-copy shared memory, and future fiber support to the browser and other JavaScript environments.

It explores what a true low-level scheduler could look like in a world constrained by:

• Web Workers
• SharedArrayBuffers
• TypedArray alignment
• Atomics
• No thread stacks or closures across workers

Penny is not a worker pool — it is a research runtime that pushes the boundaries of what JavaScript can do on multicore hardware.

• Local worker deques backed by SharedArrayBuffers
• Work stealing using atomic CAS operations
• Avoids expensive message passing using typed SAB views
• Cross-thread task execution with a static function table
• Zero-copy argument marshalling (planned)
• WASM stack switching + continuation support (v2+)
• Dynamic IR-level yield injection (future)
• Decentralized scheduling architecture (Cilk-like)

import { Scheduler } from "./scheduler";

const scheduler = new Scheduler(4); // 4 worker threads

// define the function table ahead of time. as in /src/worker/worker.js

scheduler.newTask(1, [40, 2]);  // => 42

🧠 Why Penny Exists

Modern runtimes like Cilk, Go, Tokio, Rayon, and Java Loom all rely on:

Local work queues

Work stealing

Cooperatively yielding tasks

Continuations or virtual threads

Stack or fiber switching

Fast shared memory

JavaScript has none of these — yet all major platforms (browsers, Node, Deno, Bun) now support:

Web Workers / Worker Threads

SharedArrayBuffers

Atomics

WebAssembly

Proposed WASM stack switching

Module-level isolation and loading

Penny explores whether a real multicore scheduler can be built using only these primitives.

Each worker has a dedicated SAB slice containing:

State

Identifiers

Top/Bottom deque pointers

A ring buffer for tasks

Workers run an infinite loop:

Pop from bottom (fast path)

If empty → steal from another worker’s top

If all empty → check global MPMC queue

If still empty → Atomics.wait()

Main thread only injects tasks; it does not schedule them

Future versions may move scheduling into a dedicated "scheduler worker"

📄 Full details: 👉 docs/architecture.md

Penny is experimental and rapidly evolving. Not intended for production use.