Class RpcWorkerPool

ch6-thread-pool/rpc-worker.js:5–66

const STRATEGIES = new Set([ 'roundrobin', 'random', 'leastbusy' ]);

module.exports = class RpcWorkerPool {
  constructor(path, size = 0, strategy = 'roundrobin') {
    if (size === 0)     this.size = CORES; // <1>
    else if (size < 0)  this.size = Math.max(CORES + size, 1);
    else                this.size = size;

    if (!STRATEGIES.has(strategy)) throw new TypeError('invalid strategy');
    this.strategy = strategy; // <2>
    this.rr_index = -1;

    this.next_command_id = 0;
    this.workers = []; // <3>
    for (let i = 0; i < this.size; i++) {
      const worker = new Worker(path);
      this.workers.push({ worker, in_flight_commands: new Map() }); // <4>
      worker.on('message', (msg) => {
        this.onMessageHandler(msg, i);
      });
    }
  }
// THIS LINE SHOULD NOT APPEAR IN PRINT
  onMessageHandler(msg, worker_id) {
    const worker = this.workers[worker_id];
    const { result, error, id } = msg;
    const { resolve, reject } = worker.in_flight_commands.get(id);
    worker.in_flight_commands.delete(id);
    if (error) reject(error);
    else resolve(result);
  }
// THIS LINE SHOULD NOT APPEAR IN PRINT
  exec(method, ...args) {
    const id = ++this.next_command_id;
    let resolve, reject;
    const promise = new Promise((res, rej) => { resolve = res; reject = rej; });
    const worker = this.getWorker(); // <1>
    worker.in_flight_commands.set(id, { resolve, reject });
    worker.worker.postMessage({ method, params: args, id });
    return promise;
  }
// THIS LINE SHOULD NOT APPEAR IN PRINT
  getWorker() {
    let id;
    if (this.strategy === 'random') {
      id = Math.floor(Math.random() * this.size);
    } else if (this.strategy === 'roundrobin') {
      this.rr_index++;
      if (this.rr_index >= this.size) this.rr_index = 0;
      id = this.rr_index;
    } else if (this.strategy === 'leastbusy') {
      let min = Infinity;
      for (let i = 0; i < this.size; i++) {
        let worker = this.workers[i];
        if (worker.in_flight_commands.size < min) {
          min = worker.in_flight_commands.size;
          id = i;
        }
      }
    }