src/pools/thread/dynamic.ts

   1 import type { JSONValue, MessageValue } from '../../utility-types'
   2 import type { PoolOptions } from '../abstract-pool'
   3 import type { ThreadWorkerWithMessageChannel } from './fixed'
   4 import { FixedThreadPool } from './fixed'
   5
   6 /**
   7  * A thread pool with a dynamic number of threads, but a guaranteed minimum number of threads.
   8  *
   9  * This thread pool creates new threads when the others are busy, up to the maximum number of threads.
  10  * When the maximum number of threads is reached, an event is emitted. If you want to listen to this event, use the pool's `emitter`.
  11  *
  12  * @template Data Type of data sent to the worker.
  13  * @template Response Type of response of execution.
  14  *
  15  * @author [Alessandro Pio Ardizio](https://github.com/pioardi)
  16  * @since 0.0.1
  17  */
  18 export class DynamicThreadPool<
  19   Data extends JSONValue = JSONValue,
  20   Response extends JSONValue = JSONValue
  21 > extends FixedThreadPool<Data, Response> {
  22   /**
  23    * Constructs a new poolifier dynamic thread pool.
  24    *
  25    * @param min Minimum number of threads which are always active.
  26    * @param max Maximum number of threads that can be created by this pool.
  27    * @param filename Path to an implementation of a `ThreadWorker` file, which can be relative or absolute.
  28    * @param opts Options for this fixed thread pool. Default: `{ maxTasks: 1000 }`
  29    */
  30   public constructor (
  31     min: number,
  32     public readonly max: number,
  33     filename: string,
  34     opts: PoolOptions<ThreadWorkerWithMessageChannel> = { maxTasks: 1000 }
  35   ) {
  36     super(min, filename, opts)
  37   }
  38
  39   /**
  40    * Choose a thread for the next task.
  41    *
  42    * It will first check for and return an idle thread.
  43    * If all threads are busy, then it will try to create a new one up to the `max` thread count.
  44    * If the max thread count is reached, the emitter will emit a `FullPool` event and it will fall back to using a round robin algorithm to distribute the load.
  45    *
  46    * @returns Thread worker.
  47    */
  48   protected chooseWorker (): ThreadWorkerWithMessageChannel {
  49     let worker: ThreadWorkerWithMessageChannel | undefined
  50     for (const entry of this.tasks) {
  51       if (entry[1] === 0) {
  52         worker = entry[0]
  53         break
  54       }
  55     }
  56
  57     if (worker) {
  58       // a worker is free, use it
  59       return worker
  60     } else {
  61       if (this.workers.length === this.max) {
  62         this.emitter.emit('FullPool')
  63         return super.chooseWorker()
  64       }
  65       // all workers are busy create a new worker
  66       const worker = this.internalNewWorker()
  67       worker.port2?.on('message', (message: MessageValue<Data>) => {
  68         if (message.kill) {
  69           this.sendToWorker(worker, { kill: 1 })
  70           void this.destroyWorker(worker)
  71           this.removeWorker(worker)
  72         }
  73       })
  74       return worker
  75     }
  76   }
  77 }