main.js

const { ipcMain, BrowserWindow, app } = require("electron");
const path = require("path");
app.allowRendererProcessReuse = true;
const cpus = require("os").cpus().length;
console.log("cpus: " + cpus);

// stack of available background threads
var available = [];

// queue of tasks to be done
var tasks = [];

// hand the tasks out to waiting threads
function doIt() {
  while (available.length > 0 && tasks.length > 0) {
    var task = tasks.shift();
    available.shift().send(task[0], task[1]);
  }
  renderer.webContents.send("status", available.length, tasks.length);
}

// Create a hidden background window
function createBgWindow() {
  result = new BrowserWindow({
    show: false,
    webPreferences: {
      preload: path.join(__dirname, "preload.js"),
    },
  });
  result.loadURL("file://" + __dirname + "/background.html");
  result.on("closed", () => {
    console.log("background window closed");
  });
  return result;
}

app.whenReady().then(function () {
  // Create the "renderer" window which contains the visible UI
  renderer = new BrowserWindow({
    width: 500,
    height: 400,
    webPreferences: {
      preload: path.join(__dirname, "preload.js"),
    },
  });
  renderer.loadURL("file://" + __dirname + "/renderer.html");
  renderer.show();
  renderer.on("closed", () => {
    // call quit to exit, otherwise the background windows will keep the app running
    app.quit();
  });

  // create background thread for each cpu
  for (var i = 0; i < cpus; i++) createBgWindow();

  // Main thread can receive directly from windows
  ipcMain.on("to-main", (event, arg) => {
    console.log(arg);
  });

  // Windows can talk to each other via main
  ipcMain.on("for-renderer", (event, arg) => {
    renderer.webContents.send("to-renderer", arg);
  });
  ipcMain.on("for-background", (event, arg) => {
    tasks.push(["message", arg]);
    doIt();
  });

  // heavy processing done in the background thread
  // so UI and main threads remain responsive
  ipcMain.on("assign-task", (event, arg) => {
    tasks.push(["task", arg]);
    doIt();
  });

  ipcMain.on("ready", (event, arg) => {
    available.push(event.sender);
    doIt();
  });
});