Playing around with worker_threads

worker_thread_test.js

const {Worker, isMainThread, parentPort, workerData} = require('worker_threads');

const gameIdToWorker = new Map();
const gameIds = []; // Not required.  just makes it easy to pick a random game id

let messageCount = 0;

/** Initialize a worker thread */
function makeWorker(workerId) {
  const worker = new Worker(__filename, {workerData: {workerId}});

  // Handle messages from worker
  worker.on('message', msg => {
    messageCount++;
    if (messageCount % 10000 == 0) {
      console.log(`Game action #${messageCount}`, msg);
    }
  });

  // Lifecycle events
  worker.on('error', err => console.error('Error', workerId, err));
  worker.on('exit', code => console.log('EXIT', workerId, code));

  // Create some games for the worker to manage
  for (let i = 0; i < 3; i++) {
    // Pick an id for the gamej
    const gameId = workerId * 100 + 1;

    // Tell worker to create the game
    worker.postMessage({action: 'create', gameId});

    // Keep track of which workers have which games
    gameIdToWorker.set(gameId, worker);

    gameIds.push(gameId); // So we can easily pick games at random
  }
}

/** Simulate game actions, self-invokes as rapidly as possible*/
function doSomeGameAction() {
  const gameId = gameIds[Math.floor(Math.random() * gameIds.length)];
  const worker = gameIdToWorker.get(gameId);

  if (!worker) throw Error(`Invalid worker ${gameId}`);
  worker.postMessage({action: 'poke', gameId});

  // ... and repeat ASAP
  setImmediate(doSomeGameAction);
}

if (isMainThread) {
  // Create some workers
  const numCPUs = require('os').cpus().length;
  for (let i = 0; i < numCPUs; i++) makeWorker(i);

  // Start simulating game actions
  doSomeGameAction();
} else {
  const config = workerData;

  // Minimal game class with state and an action method
  class Game {
    count = 0;

    poke() {
      this.count++
    }
  }

  // Games this worker is responsible for
  const games = new Map();

  // Handle messages from parent
  parentPort.on('message', msg => {
    switch (msg.action) {
      case 'config':
        break;

      case 'create':
        games.set(msg.gameId, new Game());
        break;

      case 'poke':
        const game = games.get(msg.gameId);

        // Update game state
        game.poke();

        // Pass state back to main thread
        parentPort.postMessage({gameId: msg.gameId, count: game.count});

        break;
    }
  });

  console.log(`Worker ${config.workerId} ready`);
}