lib/dynamic.js

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