Async.Queue usage

task.js

/**
 * Prgram to test async.queue usage
 *  - gerenates tasks at the rate of "taskGenRate"
 *  - tasks are proocessed at the rate of "taskProcessRate"
 *  - process is paused when queue size reaches "maxQueueSize"
 */

const async = require('async');

let i = 0;
let paused = false;
const maxQueueSize = 20;
const taskGenRate = 100;
const taskProcessRate = 1000;

const q = async.queue( (task, cb) => {
  serviceTask(task)
      .then(cb);
}, 1);

q.drain(() => {
  let ts = new Date();
  ts = ts.toISOString();
  console.log(`${ts} : ### Queue Drained`);
  if (paused) {
    console.log(`${ts} : ### Resume`);
    paused = false;
  }
});

// Generate tasks at regular interval
setInterval( () => {
  if (!paused) {
    i++;
    const task = {index: i, a: Math.floor(Math.random()*10)};
    let ts = new Date();
    ts = ts.toISOString();
    console.log(`${ts} : + ADDING task ${JSON.stringify(task)}`);
    q.push(task);
    console.log(`${ts} : queue length: ${q.length()}`);
    if (q.length() >= maxQueueSize) {
      console.log(`${ts} : ### Pause`);
      paused = true;
    }
  }
}, taskGenRate);

const serviceTask = (task) => {
  return new Promise( (resolve, reject) => {
    setTimeout( () => {
      let ts = new Date();
      ts = ts.toISOString();
      console.log(`${ts} : > RUNNING task ${JSON.stringify(task)}`);
      resolve();
    }, taskProcessRate);
  });
};