WasmWorker.js

import * as Comlink from "comlink" // todo: maybe only import Comlink.expose?
import WasmRunner from "./WasmRunner"

class WasmWorker extends WasmRunner {

    _pauseBuffer
    _stdinBuffer

    constructor(pauseBuffer, stdinBuffer) { super()
        // buffers can be accessed both from the main thread and the worker
        this._pauseBuffer = pauseBuffer // used to pause/resume worker execution
        this._stdinBuffer = stdinBuffer // used to pass user inputs to worker
    }

    // note: running commands is handled by parent class


    /* pausing and resuming */

    pauseExecution() {
        console.log("pausing worker execution")
        Atomics.store(this._pauseBuffer, 0, 1) // mem[0] = 1 (means hold)
        Atomics.wait(this._pauseBuffer, 0, 1) // wait while value is 1
        console.log("resuming worker execution")
    }

    resumeExecution() {
        console.log("resuming worker execution")
        Atomics.store(this._pauseBuffer, 0, 0) // mem[0] = 0 (means do not hold)
        // note: this method is just for completeness (the worker will be
        // resumed from outside by changing the pause buffer value)
    }


    /* input output handling */

    _readStdinBuffer(index = null) { // null = read all
        if(index != null) return Atomics.load(this._stdinBuffer, index)
        let result = []
        for(let i = 0; i < this._stdinBuffer.length; i++) {
            const value = Atomics.load(this._stdinBuffer, i)
            if(value === 0) break // 0 marks end of input
            result.push(value)
        }
        return result
    }

    // handles stdin calls from emscr (pause -> call stdin proxy -> deliver)
    _onEmscrStdinCall(tty, stdinProxy, stdoutProxy, stderrProxy) {
        if(tty.input.length == 0) {

            // read input (will set stdin buffer)
            stdinProxy(this.outputBuffer.split(/\r?\n/g).pop())
            this.pauseExecution() // resumes after input

            // copy stdin buffer to tty input
            tty.input = this._readStdinBuffer()
            this.outputBuffer += tty.input.map(c => String.fromCharCode(c)).join("")

            if(tty.input.length == 0) return null
            else tty.input.push(null) // marks end
        }

        // deliver input
        return tty.input.shift()
    }

    // handles stdin calls from wasmer
    _wasmerStdinCallCounter = 0
    _onWasmerStdinCall(stdinBuffer, stdinProxy, stdoutProxy, stderrProxy) {

        // second read means end of string
        if(this._wasmerStdinCallCounter % 2 !== 0) {
            this._wasmerStdinCallCounter++; return 0 }

        // read input (will set stdin buffer)
        stdinProxy(this.outputBuffer.split(/\r?\n/g).pop())
        this.pauseExecution() // resumes after input

        // copy stdin buffer to stdinBuffer
        const _stdinBuffer = this._readStdinBuffer()
        _stdinBuffer.forEach((char, i) => stdinBuffer[i] = char)
        this.outputBuffer += _stdinBuffer.map(c => String.fromCharCode(c)).join("")

        // indicate we've read once
        this._wasmerStdinCallCounter++

        // return how much to read
        return _stdinBuffer.length

    }


    /* expose (sets up comlink communication) */

    static expose() {
        if(typeof Comlink == "undefined" && WasmWorker.isWorkerScope())
            importScripts("https://cdn.jsdelivr.net/npm/comlink@4.3.1/dist/umd/comlink.min.js")
        // note: the bundle would get smaller if we would always load Comlink from CDN ..
        Comlink.expose(WasmWorker)
    }

    static isWorkerScope() { // checks if script is executed in worker or main thread
        return (typeof WorkerGlobalScope != "undefined" && self instanceof WorkerGlobalScope)
    }

}

// if this runs in worker scope -> expose
if(WasmWorker.isWorkerScope()) WasmWorker.expose()

export default WasmWorker