src/pools/thread/dynamic.ts

   1 import type { JSONValue } from '../../utility-types'
   2 import { isKillBehavior, KillBehaviors } from '../../worker/worker-options'
   3 import type { PoolOptions } from '../abstract-pool'
   4 import type { ThreadWorkerWithMessageChannel } from './fixed'
   5 import { FixedThreadPool } from './fixed'
   6
   7 /**
   8  * A thread pool with a dynamic number of threads, but a guaranteed minimum number of threads.
   9  *
  10  * This thread pool creates new threads when the others are busy, up to the maximum number of threads.
  11  * 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`.
  12  *
  13  * @template Data Type of data sent to the worker.
  14  * @template Response Type of response of execution.
  15  *
  16  * @author [Alessandro Pio Ardizio](https://github.com/pioardi)
  17  * @since 0.0.1
  18  */
  19 export class DynamicThreadPool<
  20   Data extends JSONValue = JSONValue,
  21   Response extends JSONValue = JSONValue
  22 > extends FixedThreadPool<Data, Response> {
  23   /**
  24    * Constructs a new poolifier dynamic thread pool.
  25    *
  26    * @param min Minimum number of threads which are always active.
  27    * @param max Maximum number of threads that can be created by this pool.
  28    * @param filePath Path to an implementation of a `ThreadWorker` file, which can be relative or absolute.
  29    * @param opts Options for this dynamic thread pool. Default: `{ maxTasks: 1000 }`
  30    */
  31   public constructor (
  32     min: number,
  33     public readonly max: number,
  34     filePath: string,
  35     opts: PoolOptions<ThreadWorkerWithMessageChannel> = { maxTasks: 1000 }
  36   ) {
  37     super(min, filePath, opts)
  38   }
  39
  40   /**
  41    * Choose a thread for the next task.
  42    *
  43    * It will first check for and return an idle thread.
  44    * If all threads are busy, then it will try to create a new one up to the `max` thread count.
  45    * 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.
  46    *
  47    * @returns Thread worker.
  48    */
  49   protected chooseWorker (): ThreadWorkerWithMessageChannel {
  50     for (const [worker, numberOfTasks] of this.tasks) {
  51       if (numberOfTasks === 0) {
  52         // A worker is free, use it
  53         return worker
  54       }
  55     }
  56
  57     if (this.workers.length === this.max) {
  58       this.emitter.emit('FullPool')
  59       return super.chooseWorker()
  60     }
  61
  62     // All workers are busy, create a new worker
  63     const workerCreated = this.createAndSetupWorker()
  64     this.registerWorkerMessageListener<Data>(workerCreated, message => {
  65       const tasksInProgress = this.tasks.get(workerCreated)
  66       if (
  67         isKillBehavior(KillBehaviors.HARD, message.kill) ||
  68         tasksInProgress === 0
  69       ) {
  70         // Kill received from the worker, means that no new tasks are submitted to that worker for a while ( > maxInactiveTime)
  71         void this.destroyWorker(workerCreated)
  72       }
  73     })
  74     return workerCreated
  75   }
  76 }