Reading files in Worklets

[Bialson]

Hello everyone,

I'm currently implementing a custom file reader for tus-js-client to address Memory issues on Android. The standard Blob implementation throws an OutOfMemory error when handling files larger than 100 MB.

To optimize performance and avoid overhead on the main JS thread, I'm considering moving the file reading logic to a worklet. Does anyone know if it's possible to use expo-file-system (or a similar library) within a worklet to read raw bytes?

Any insights or architectural advice would be greatly appreciated!

[tjzel]

Hi @Bialson. AFAIK Expo is currently working on an experimental iteration of a feature of using Expo Modules on multiple runtimes - I assume that means that Expo libraries like expo-file-system wouldn't work in this context at this moment. By (current) design TurboModules also can't be used on other runtimes.

If you had a library that, for instance, operate via a HostObject in JavaScript (which is not a TurboModule) you could copy it to a Worklet Runtime and use it there, from another thread. Unfortunately I don't know whether such a library exists. However, if it would indeed exist, then you could use it somewhat like this:

import {createFileManager} from 'some-library';
import {createWorkletRuntime, scheduleOnRuntime} from 'react-native-worklets';

const fileManager = createFileManager(); // a HostObject

const runtime = createWorkletRuntime();

scheduleOnRuntime(() => {
  'worklet';
  fileManager.readBlob('/bigBlob'); // fileManager is implicitly copied to another runtime here
});