mirror of
https://github.com/oven-sh/bun
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## Summary Implements a string fast path optimization for `postMessage` and `structuredClone` operations that provides significant performance improvements for string-only data transfer, along with various bug fixes and infrastructure improvements. ## Key Performance Improvements **postMessage with Workers:** - **Small strings (11 chars):** ~5% faster (572ns vs 599ns) - **Medium strings (14KB):** **~2.7x faster** (528ns vs 1.40μs) - **Large strings (3MB):** **~660x faster** (540ns vs 356μs) **Compared to Node.js postMessage:** - Similar performance for small strings - Competitive for medium strings - **~455x faster** for large strings (540ns vs 245μs) ## Implementation Details The optimization adds a **string fast path** that bypasses full structured cloning serialization when: - Input is a pure string (`value.isString()`) - No transfer list or message ports are involved - Not being stored persistently ### Core Changes **String Thread-Safety Utilities (`BunString.cpp/h`):** - `isCrossThreadShareable()` - Checks if string can be safely shared across threads - `toCrossThreadShareable()` - Converts strings to thread-safe form via `isolatedCopy()` - Handles edge cases: atoms, symbols, substring slices, external buffers **Serialization Fast Path (`SerializedScriptValue.cpp`):** - New `m_fastPathString` field stores string data directly - Bypasses full object serialization machinery for pure strings - Creates isolated copies for cross-thread safety **Deserialization Fast Path:** - Directly returns JSString from stored string data - Avoids parsing serialized byte streams **Updated Flags System (`JSValue.zig`, `Serialization.cpp`):** - Replaces boolean `forTransfer` with structured `SerializedFlags` - Supports `forCrossProcessTransfer` and `forStorage` distinctions **Structured Clone Infrastructure:** - Moved `structuredClone` implementation to dedicated `StructuredClone.cpp` - Added `jsFunctionStructuredCloneAdvanced` for testing with custom flags - Improved class serialization compatibility checks (`isForTransfer`, `isForStorage`) **IPC Improvements (`ipc.zig`):** - Fixed race conditions in `SendQueue` by deferring cleanup to next tick - Proper fd ownership handling with `bun.take()` - Cached IPC serialize/parse functions for better performance **BlockList Thread Safety Fixes (`BlockList.zig`):** - Fixed potential deadlocks by moving mutex locking inside methods - Added atomic `estimated_size` counter to avoid lock during GC - Corrected pointer handling in comparison functions - Improved GC safety in `rules()` method ## Benchmark Results ``` ❯ bun-21926 bench/string-postmessage.mjs # This branch postMessage(11 chars string) 572.24 ns/iter postMessage(14 KB string) 527.55 ns/iter ← ~2.7x faster postMessage(3 MB string) 539.70 ns/iter ← ~660x faster ❯ bun-1.2.20 bench/string-postmessage.mjs # Previous postMessage(11 chars string) 598.76 ns/iter postMessage(14 KB string) 1.40 µs/iter postMessage(3 MB string) 356.38 µs/iter ❯ node bench/string-postmessage.mjs # Node.js comparison postMessage(11 chars string) 569.63 ns/iter postMessage(14 KB string) 1.46 µs/iter postMessage(3 MB string) 245.46 µs/iter ``` **Key insight:** The fast path achieves **constant time performance** regardless of string size (~540ns), while traditional serialization scales linearly with data size. ## Test Coverage **New Tests:** - `test/js/web/structured-clone-fastpath.test.ts` - Fast path memory usage validation - `test/js/web/workers/structuredClone-classes.test.ts` - Comprehensive class serialization tests - Tests ArrayBuffer transferability - Tests BunFile cloning with storage/transfer restrictions - Tests net.BlockList cloning behavior - Validates different serialization contexts (default, worker, window) **Enhanced Tests:** - `test/js/web/workers/structured-clone.test.ts` - Multi-function testing - Tests `structuredClone`, `jscSerializeRoundtrip`, and cross-process serialization - Validates consistency across different serialization paths - `test/js/node/cluster.test.ts` - Better error handling and debugging **Benchmarks:** - `bench/string-postmessage.mjs` - Worker postMessage performance comparison - `bench/string-fastpath.mjs` - Fast path vs traditional serialization comparison ## Bug Fixes **BlockList Threading Issues:** - Fixed potential deadlocks when multiple threads access BlockList simultaneously - Moved mutex locks inside methods rather than holding across entire function calls - Added atomic size tracking for GC compatibility - Fixed comparison function pointer handling **IPC Race Conditions:** - Fixed race condition where `SendQueue._onAfterIPCClosed()` could be called on wrong thread - Deferred cleanup operations to next tick using task queue - Improved file descriptor ownership with proper `bun.take()` usage **Structured Clone Compatibility:** - Enhanced class serialization with proper transfer/storage mode checking - Fixed edge cases where non-transferable objects were incorrectly handled - Added better error reporting for unsupported clone operations ## Technical Notes - Thread safety ensured via `String.isolatedCopy()` for cross-VM transfers - Memory cost calculation updated to account for string references - Maintains full compatibility with existing structured clone semantics - Does not affect object serialization or transfer lists - Proper cleanup and error handling throughout IPC pipeline --------- Co-authored-by: Jarred Sumner <jarred@jarredsumner.com> Co-authored-by: autofix-ci[bot] <114827586+autofix-ci[bot]@users.noreply.github.com> Co-authored-by: Meghan Denny <meghan@bun.sh>
Bun
Read the docs →
What is Bun?
Bun is an all-in-one toolkit for JavaScript and TypeScript apps. It ships as a single executable called bun.
At its core is the Bun runtime, a fast JavaScript runtime designed as a drop-in replacement for Node.js. It's written in Zig and powered by JavaScriptCore under the hood, dramatically reducing startup times and memory usage.
bun run index.tsx # TS and JSX supported out-of-the-box
The bun command-line tool also implements a test runner, script runner, and Node.js-compatible package manager. Instead of 1,000 node_modules for development, you only need bun. Bun's built-in tools are significantly faster than existing options and usable in existing Node.js projects with little to no changes.
bun test # run tests
bun run start # run the `start` script in `package.json`
bun install <pkg> # install a package
bunx cowsay 'Hello, world!' # execute a package
Install
Bun supports Linux (x64 & arm64), macOS (x64 & Apple Silicon) and Windows (x64).
Linux users — Kernel version 5.6 or higher is strongly recommended, but the minimum is 5.1.
x64 users — if you see "illegal instruction" or similar errors, check our CPU requirements
# with install script (recommended)
curl -fsSL https://bun.com/install | bash
# on windows
powershell -c "irm bun.com/install.ps1 | iex"
# with npm
npm install -g bun
# with Homebrew
brew tap oven-sh/bun
brew install bun
# with Docker
docker pull oven/bun
docker run --rm --init --ulimit memlock=-1:-1 oven/bun
Upgrade
To upgrade to the latest version of Bun, run:
bun upgrade
Bun automatically releases a canary build on every commit to main. To upgrade to the latest canary build, run:
bun upgrade --canary
Quick links
-
Intro
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Templating
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CLI
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Runtime
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Package manager
-
Bundler
-
Test runner
-
Package runner
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API
- HTTP server (
Bun.serve) - WebSockets
- Workers
- Binary data
- Streams
- File I/O (
Bun.file) - import.meta
- SQLite (
bun:sqlite) - PostgreSQL (
Bun.sql) - Redis (
Bun.redis) - S3 Client (
Bun.s3) - FileSystemRouter
- TCP sockets
- UDP sockets
- Globals
- $ Shell
- Child processes (spawn)
- Transpiler (
Bun.Transpiler) - Hashing
- Colors (
Bun.color) - Console
- FFI (
bun:ffi) - C Compiler (
bun:fficc) - HTMLRewriter
- Testing (
bun:test) - Cookies (
Bun.Cookie) - Utils
- Node-API
- Glob (
Bun.Glob) - Semver (
Bun.semver) - DNS
- fetch API extensions
- HTTP server (
Guides
-
Binary
- Convert a Blob to a string
- Convert a Buffer to a blob
- Convert a Blob to a DataView
- Convert a Buffer to a string
- Convert a Blob to a ReadableStream
- Convert a Blob to a Uint8Array
- Convert a DataView to a string
- Convert a Uint8Array to a Blob
- Convert a Blob to an ArrayBuffer
- Convert an ArrayBuffer to a Blob
- Convert a Buffer to a Uint8Array
- Convert a Uint8Array to a Buffer
- Convert a Uint8Array to a string
- Convert a Buffer to an ArrayBuffer
- Convert an ArrayBuffer to a Buffer
- Convert an ArrayBuffer to a string
- Convert a Uint8Array to a DataView
- Convert a Buffer to a ReadableStream
- Convert a Uint8Array to an ArrayBuffer
- Convert an ArrayBuffer to a Uint8Array
- Convert an ArrayBuffer to an array of numbers
- Convert a Uint8Array to a ReadableStream
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Ecosystem
- Use React and JSX
- Use EdgeDB with Bun
- Use Prisma with Bun
- Add Sentry to a Bun app
- Create a Discord bot
- Run Bun as a daemon with PM2
- Use Drizzle ORM with Bun
- Build an app with Nuxt and Bun
- Build an app with Qwik and Bun
- Build an app with Astro and Bun
- Build an app with Remix and Bun
- Build a frontend using Vite and Bun
- Build an app with Next.js and Bun
- Run Bun as a daemon with systemd
- Deploy a Bun application on Render
- Build an HTTP server using Hono and Bun
- Build an app with SvelteKit and Bun
- Build an app with SolidStart and Bun
- Build an HTTP server using Elysia and Bun
- Build an HTTP server using StricJS and Bun
- Containerize a Bun application with Docker
- Build an HTTP server using Express and Bun
- Use Neon Postgres through Drizzle ORM
- Server-side render (SSR) a React component
- Read and write data to MongoDB using Mongoose and Bun
- Use Neon's Serverless Postgres with Bun
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HTMLRewriter
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HTTP
- Hot reload an HTTP server
- Common HTTP server usage
- Write a simple HTTP server
- Configure TLS on an HTTP server
- Send an HTTP request using fetch
- Proxy HTTP requests using fetch()
- Start a cluster of HTTP servers
- Stream a file as an HTTP Response
- fetch with unix domain sockets in Bun
- Upload files via HTTP using FormData
- Streaming HTTP Server with Async Iterators
- Streaming HTTP Server with Node.js Streams
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Install
- Add a dependency
- Add a Git dependency
- Add a peer dependency
- Add a trusted dependency
- Add a development dependency
- Add a tarball dependency
- Add an optional dependency
- Generate a yarn-compatible lockfile
- Configuring a monorepo using workspaces
- Install a package under a different name
- Install dependencies with Bun in GitHub Actions
- Using bun install with Artifactory
- Configure git to diff Bun's lockb lockfile
- Override the default npm registry for bun install
- Using bun install with an Azure Artifacts npm registry
- Migrate from npm install to bun install
- Configure a private registry for an organization scope with bun install
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Process
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Read file
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Runtime
- Delete files
- Run a Shell Command
- Import a JSON file
- Import a TOML file
- Set a time zone in Bun
- Set environment variables
- Re-map import paths
- Delete directories
- Read environment variables
- Import a HTML file as text
- Install and run Bun in GitHub Actions
- Debugging Bun with the web debugger
- Install TypeScript declarations for Bun
- Debugging Bun with the VS Code extension
- Inspect memory usage using V8 heap snapshots
- Define and replace static globals & constants
- Codesign a single-file JavaScript executable on macOS
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Streams
- Convert a ReadableStream to JSON
- Convert a ReadableStream to a Blob
- Convert a ReadableStream to a Buffer
- Convert a ReadableStream to a string
- Convert a ReadableStream to a Uint8Array
- Convert a ReadableStream to an array of chunks
- Convert a Node.js Readable to JSON
- Convert a ReadableStream to an ArrayBuffer
- Convert a Node.js Readable to a Blob
- Convert a Node.js Readable to a string
- Convert a Node.js Readable to an Uint8Array
- Convert a Node.js Readable to an ArrayBuffer
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Test
- Spy on methods in
bun test - Bail early with the Bun test runner
- Mock functions in
bun test - Run tests in watch mode with Bun
- Use snapshot testing in
bun test - Skip tests with the Bun test runner
- Using Testing Library with Bun
- Update snapshots in
bun test - Run your tests with the Bun test runner
- Set the system time in Bun's test runner
- Set a per-test timeout with the Bun test runner
- Migrate from Jest to Bun's test runner
- Write browser DOM tests with Bun and happy-dom
- Mark a test as a "todo" with the Bun test runner
- Re-run tests multiple times with the Bun test runner
- Generate code coverage reports with the Bun test runner
- import, require, and test Svelte components with bun test
- Set a code coverage threshold with the Bun test runner
- Spy on methods in
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Util
- Generate a UUID
- Hash a password
- Escape an HTML string
- Get the current Bun version
- Encode and decode base64 strings
- Compress and decompress data with gzip
- Sleep for a fixed number of milliseconds
- Detect when code is executed with Bun
- Check if two objects are deeply equal
- Compress and decompress data with DEFLATE
- Get the absolute path to the current entrypoint
- Get the directory of the current file
- Check if the current file is the entrypoint
- Get the file name of the current file
- Convert a file URL to an absolute path
- Convert an absolute path to a file URL
- Get the absolute path of the current file
- Get the path to an executable bin file
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WebSocket
-
Write file
Contributing
Refer to the Project > Contributing guide to start contributing to Bun.
License
Refer to the Project > License page for information about Bun's licensing.