---
title: "Improving our parallel intrinsic · baby steps"
url: https://daily.dev/posts/improving-our-parallel-intrinsic-baby-steps-kg4vp5ivm
source_url: https://smallcultfollowing.com/babysteps/blog/2012/12/06/improving-our-parallel-intrinsic
type: article
source: "Niko Matsakis - baby steps"
published: 2026-05-31T07:54:14.466Z
updated: 2026-05-31T09:20:05.611Z
tags: ["javascript"]
reading_time: 12
upvotes: 0
comments: 0
language: en
---

> ## Documentation Index
> Fetch the complete documentation index at: https://daily.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Improving our parallel intrinsic · baby steps

**[Niko Matsakis - baby steps](https://daily.dev/sources/babysteps)** · 12 min read · 0 upvotes · 0 comments

## Summary

A deep dive into the internals of SpiderMonkey's parallel execution primitive `%ParallelBuildArray()`, examining its design flaws and proposing improvements. The post covers how the current intrinsic works — including the warmup phase, IonMonkey JIT compilation for parallel execution, and thread-safety hacks — then proposes replacing it with a more general `%ForkJoin()` primitive paired with `%UnsafeSetElement()`. A key improvement eliminates the warmup phase entirely by using sequential fallback iterations as implicit warmup, with the parallel attempt retried after each chunk. Additional enhancements like avoiding array initialization overhead and detecting inherently non-parallelizable functions are also sketched out.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://smallcultfollowing.com/babysteps/blog/2012/12/06/improving-our-parallel-intrinsic>

---

Tags: [#javascript](https://daily.dev/tags/javascript)

[View this post on daily.dev](https://daily.dev/posts/improving-our-parallel-intrinsic-baby-steps-kg4vp5ivm)