lib/dynamic.js

   1 'use strict'
   2 const FixedThreadPool = require('./fixed')
   3 const { randomWorker } = require('./util')
   4 const EventEmitter = require('events')
   5 class MyEmitter extends EventEmitter {}
   6
   7 /**
   8  * A thread pool with a min/max number of threads , is possible to execute tasks in sync or async mode as you prefer. <br>
   9  * This thread pool will create new workers when the other ones are busy, until the max number of threads,
  10  * when the max number of threads is reached, an event will be emitted , if you want to listen this event use the emitter method.
  11  * @author Alessandro Pio Ardizio
  12  * @since 0.0.1
  13  */
  14 class DynamicThreadPool extends FixedThreadPool {
  15   /**
  16     *
  17     * @param {Number} min  Min number of threads that will be always active
  18     * @param {Number} max  Max number of threads that will be active
  19     * @param {Object} an object with possible options for example maxConcurrency
  20   */
  21   constructor (min, max, filename, opts) {
  22     super(min, filename, opts)
  23     this.max = max
  24     this.emitter = new MyEmitter()
  25   }
  26
  27   _chooseWorker () {
  28     let worker
  29     for (const entry of this.tasks) {
  30       if (entry[1] === 0) {
  31         worker = entry[0]
  32         break
  33       }
  34     }
  35
  36     if (worker) {
  37       // a worker is free, use it
  38       return worker
  39     } else {
  40       if (this.workers.length === this.max) {
  41         this.emitter.emit('FullPool')
  42         return randomWorker(this.tasks)
  43       }
  44       // all workers are busy create a new worker
  45       const worker = this._newWorker()
  46       worker.port2.on('message', (message) => {
  47         if (message.kill) {
  48           worker.postMessage({ kill: 1 })
  49           worker.terminate()
  50         }
  51       })
  52       return worker
  53     }
  54   }
  55 }
  56
  57 module.exports = DynamicThreadPool