lib/dynamic.js

   1 'use strict'
   2 const FixedThreadPool = require('./fixed')
   3 const EventEmitter = require('events')
   4 class MyEmitter extends EventEmitter {}
   5
   6 /**
   7  * A thread pool with a min/max number of threads , is possible to execute tasks in sync or async mode as you prefer. <br>
   8  * This thread pool will create new workers when the other ones are busy, until the max number of threads,
   9  * when the max number of threads is reached, an event will be emitted , if you want to listen this event use the emitter method.
  10  * @author Alessandro Pio Ardizio
  11  * @since 0.0.1
  12  */
  13 class DynamicThreadPool extends FixedThreadPool {
  14   /**
  15     *
  16     * @param {Number} min  Min number of threads that will be always active
  17     * @param {Number} max  Max number of threads that will be active
  18   */
  19   constructor (min, max, filename, opts) {
  20     super(min, filename, opts)
  21     this.max = max
  22     this.emitter = new MyEmitter()
  23   }
  24
  25   _chooseWorker () {
  26     let worker
  27     for (const entry of this.tasks) {
  28       if (entry[1] === 0) {
  29         worker = entry[0]
  30         break
  31       }
  32     }
  33
  34     if (worker) {
  35       // a worker is free, use it
  36       return worker
  37     } else {
  38       if (this.workers.length === this.max) {
  39         this.emitter.emit('FullPool')
  40         return super._chooseWorker()
  41       }
  42       // all workers are busy create a new worker
  43       const worker = this._newWorker()
  44       worker.port2.on('message', (message) => {
  45         if (message.kill) {
  46           worker.postMessage({ kill: 1 })
  47           worker.terminate()
  48           // clean workers from data structures
  49           const myIndex = this.workers.indexOf(worker)
  50           this.workers.splice(myIndex, 1)
  51           this.tasks.delete(worker)
  52         }
  53       })
  54       return worker
  55     }
  56   }
  57 }
  58
  59 module.exports = DynamicThreadPool