Bare Kit

Reference for bare-kit and react-native-bare-kit: the Worklet API for running an isolated Bare thread inside a native app, and the IPC channel between host and worklet.

bare-kit embeds Bare in native application development. It provides a web-worker-like API for starting and managing isolated Bare threads—called worklets—each exposing an IPC channel with bindings for several languages. react-native-bare-kit wraps the same API for React Native and Expo. For the architecture this enables, see One core, many platforms.

A worklet is an isolated Bare thread managed by the host app. The name avoids confusion with the worker threads of bare-worker.

Worklet

A worklet runs a Bare entry script on a background thread. Create one, start it with an entry filename and source, and manage its lifecycle.

Actions

start(filename, source[, arguments])— start the worklet running source as filename.
suspend()— suspend execution.
suspend(linger)— suspend, keeping the process alive for linger milliseconds before it fully exits.
resume()— resume a suspended worklet.
terminate()— terminate the worklet.

A configuration object can optionally set a memoryLimit or attach assets.

React Native

import { Worklet } from 'react-native-bare-kit'
import b4a from 'b4a'

const worklet = new Worklet()

const source = `
const { IPC } = BareKit

IPC.on('data', (data) => console.log(data.toString()))
IPC.write(Buffer.from('Hello from Bare!'))
`

worklet.start('/app.js', source)

const { IPC } = worklet
IPC.on('data', (data) => console.log(b4a.toString(data)))
IPC.write(b4a.from('Hello from React Native!'))

iOS

#import <BareKit/BareKit.h>

BareWorkletConfiguration *options = [BareWorkletConfiguration defaultWorkletConfiguration];
options.memoryLimit = 1024 * 1024 * 24; // 24 MiB

BareWorklet *worklet = [[BareWorklet alloc] initWithConfiguration:options];

NSString *source = @"console.log('hello from the worklet')";
[worklet start:@"/app.js" source:[source dataUsingEncoding:NSUTF8StringEncoding] arguments:@[]];

Android

import to.holepunch.bare.kit.Worklet;
import java.nio.charset.StandardCharsets;

Worklet.Options options = new Worklet.Options()
  .memoryLimit(24 * 1024 * 1024); // 24 MiB

Worklet worklet = new Worklet(options);

String source = "console.log('hello from the worklet')";
worklet.start("/app.js", source, StandardCharsets.UTF_8, null);

IPC

Bare Kit provides an IPC abstraction for communication between the host app and a worklet, with both synchronous and asynchronous read/write.

IPC operations are non-blocking regardless of which API you use. They may return partial results—for example writing fewer bytes than requested—and require polling to complete.

The interface is callback-driven:

readable— callback invoked when data is available to read.
writable— callback invoked when data can be written.
read()— synchronously read available data; returns nothing when none is available.
write(data)— synchronously write data; returns the number of bytes written.

Inside the worklet the channel is reached through the BareKit.IPC global (an instance of Bare.IPC); on the host it's a BareIPC (iOS) or the IPC object on the React Native Worklet.

For typed, schema-generated messaging over this channel instead of raw bytes, layer bare-rpc on top—see Type a native RPC bridge.

Loading a bundle

Instead of inline source, a worklet can start from a bundle produced by bare-pack. The entry filename's extension must be .bundle:

import { Worklet } from 'react-native-bare-kit'
import bundle from './my.bundle.js' // output by bare-pack

const worklet = new Worklet()
worklet.start('/app.bundle', bundle)

See Bundle a Bare app for producing the bundle.

Logging

console.* calls inside the worklet write to the system log (via liblog) under the bare identifier, so worklet output shows up in the platform's native logging tools.