src/pools/abstract-pool.ts

   1 import EventEmitter from 'events'
   2 import type { MessageValue } from '../utility-types'
   3 import type { IPool } from './pool'
   4
   5 /**
   6  * Callback invoked if the worker raised an error.
   7  */
   8 export type ErrorHandler<Worker> = (this: Worker, e: Error) => void
   9
  10 /**
  11  * Callback invoked when the worker has started successfully.
  12  */
  13 export type OnlineHandler<Worker> = (this: Worker) => void
  14
  15 /**
  16  * Callback invoked when the worker exits successfully.
  17  */
  18 export type ExitHandler<Worker> = (this: Worker, code: number) => void
  19
  20 /**
  21  * Basic interface that describes the minimum required implementation of listener events for a pool-worker.
  22  */
  23 export interface IWorker {
  24   on(event: 'error', handler: ErrorHandler<this>): void
  25   on(event: 'online', handler: OnlineHandler<this>): void
  26   on(event: 'exit', handler: ExitHandler<this>): void
  27   once(event: 'exit', handler: ExitHandler<this>): void
  28 }
  29
  30 /**
  31  * Options for a poolifier pool.
  32  */
  33 export interface PoolOptions<Worker> {
  34   /**
  35    * A function that will listen for error event on each worker.
  36    */
  37   errorHandler?: ErrorHandler<Worker>
  38   /**
  39    * A function that will listen for online event on each worker.
  40    */
  41   onlineHandler?: OnlineHandler<Worker>
  42   /**
  43    * A function that will listen for exit event on each worker.
  44    */
  45   exitHandler?: ExitHandler<Worker>
  46   /**
  47    * This is just to avoid non-useful warning messages.
  48    *
  49    * Will be used to set `maxListeners` on event emitters (workers are event emitters).
  50    *
  51    * @default 1000
  52    * @see [Node events emitter.setMaxListeners(n)](https://nodejs.org/api/events.html#events_emitter_setmaxlisteners_n)
  53    */
  54   maxTasks?: number
  55 }
  56
  57 /**
  58  * Internal poolifier pool emitter.
  59  */
  60 class PoolEmitter extends EventEmitter {}
  61
  62 /**
  63  * Base class containing some shared logic for all poolifier pools.
  64  *
  65  * @template Worker Type of worker which manages this pool.
  66  * @template Data Type of data sent to the worker.
  67  * @template Response Type of response of execution.
  68  */
  69 export abstract class AbstractPool<
  70   Worker extends IWorker,
  71   Data = unknown,
  72   Response = unknown
  73 > implements IPool<Data, Response> {
  74   /**
  75    * List of currently available workers.
  76    */
  77   public readonly workers: Worker[] = []
  78
  79   /**
  80    * Index for the next worker.
  81    */
  82   public nextWorkerIndex: number = 0
  83
  84   /**
  85    * - `key`: The `Worker`
  86    * - `value`: Number of tasks that has been assigned to that worker since it started
  87    */
  88   public readonly tasks: Map<Worker, number> = new Map<Worker, number>()
  89
  90   /**
  91    * Emitter on which events can be listened to.
  92    *
  93    * Events that can currently be listened to:
  94    *
  95    * - `'FullPool'`
  96    */
  97   public readonly emitter: PoolEmitter
  98
  99   /**
 100    * ID of the next message.
 101    */
 102   protected nextMessageId: number = 0
 103
 104   /**
 105    * Constructs a new poolifier pool.
 106    *
 107    * @param numberOfWorkers Number of workers that this pool should manage.
 108    * @param filePath Path to the worker-file.
 109    * @param opts Options for the pool. Default: `{ maxTasks: 1000 }`
 110    */
 111   public constructor (
 112     public readonly numberOfWorkers: number,
 113     public readonly filePath: string,
 114     public readonly opts: PoolOptions<Worker> = { maxTasks: 1000 }
 115   ) {
 116     if (!this.isMain()) {
 117       throw new Error('Cannot start a pool from a worker!')
 118     }
 119     // TODO christopher 2021-02-07: Improve this check e.g. with a pattern or blank check
 120     if (!this.filePath) {
 121       throw new Error('Please specify a file with a worker implementation')
 122     }
 123
 124     this.setupHook()
 125
 126     for (let i = 1; i <= this.numberOfWorkers; i++) {
 127       this.createAndSetupWorker()
 128     }
 129
 130     this.emitter = new PoolEmitter()
 131   }
 132
 133   /**
 134    * Number of workers that this pool should manage.
 135    *
 136    * @returns Number of workers that this pool manages.
 137    * @deprecated Only here for backward compatibility.
 138    */
 139   // eslint-disable-next-line spellcheck/spell-checker
 140   public get numWorkers (): number {
 141     return this.numberOfWorkers
 142   }
 143
 144   /**
 145    * Index for the next worker.
 146    *
 147    * @returns Index for the next worker.
 148    * @deprecated Only here for backward compatibility.
 149    */
 150   public get nextWorker (): number {
 151     return this.nextWorkerIndex
 152   }
 153
 154   public execute (data: Data): Promise<Response> {
 155     // Configure worker to handle message with the specified task
 156     const worker = this.chooseWorker()
 157     this.increaseWorkersTask(worker)
 158     const messageId = ++this.nextMessageId
 159     const res = this.internalExecute(worker, messageId)
 160     this.sendToWorker(worker, { data: data || ({} as Data), id: messageId })
 161     return res
 162   }
 163
 164   public async destroy (): Promise<void> {
 165     await Promise.all(this.workers.map(worker => this.destroyWorker(worker)))
 166   }
 167
 168   /**
 169    * Shut down given worker.
 170    *
 171    * @param worker A worker within `workers`.
 172    */
 173   protected abstract destroyWorker (worker: Worker): void | Promise<void>
 174
 175   /**
 176    * Setup hook that can be overridden by a Poolifier pool implementation
 177    * to run code before workers are created in the abstract constructor.
 178    */
 179   protected setupHook (): void {
 180     // Can be overridden
 181   }
 182
 183   /**
 184    * Should return whether the worker is the main worker or not.
 185    */
 186   protected abstract isMain (): boolean
 187
 188   /**
 189    * Increase the number of tasks that the given workers has done.
 190    *
 191    * @param worker Workers whose tasks are increased.
 192    */
 193   protected increaseWorkersTask (worker: Worker): void {
 194     const numberOfTasksTheWorkerHas = this.tasks.get(worker)
 195     if (numberOfTasksTheWorkerHas !== undefined) {
 196       this.tasks.set(worker, numberOfTasksTheWorkerHas + 1)
 197     } else {
 198       throw Error('Worker could not be found in tasks map')
 199     }
 200   }
 201
 202   /**
 203    * Removes the given worker from the pool.
 204    *
 205    * @param worker Worker that will be removed.
 206    */
 207   protected removeWorker (worker: Worker): void {
 208     // Clean worker from data structure
 209     const workerIndex = this.workers.indexOf(worker)
 210     this.workers.splice(workerIndex, 1)
 211     this.tasks.delete(worker)
 212   }
 213
 214   /**
 215    * Choose a worker for the next task.
 216    *
 217    * The default implementation uses a round robin algorithm to distribute the load.
 218    *
 219    * @returns Worker.
 220    */
 221   protected chooseWorker (): Worker {
 222     const chosenWorker = this.workers[this.nextWorkerIndex]
 223     this.nextWorkerIndex =
 224       this.workers.length - 1 === this.nextWorkerIndex
 225         ? 0
 226         : this.nextWorkerIndex + 1
 227     return chosenWorker
 228   }
 229
 230   /**
 231    * Send a message to the given worker.
 232    *
 233    * @param worker The worker which should receive the message.
 234    * @param message The message.
 235    */
 236   protected abstract sendToWorker (
 237     worker: Worker,
 238     message: MessageValue<Data>
 239   ): void
 240
 241   protected abstract registerWorkerMessageListener (
 242     port: Worker,
 243     listener: (message: MessageValue<Response>) => void
 244   ): void
 245
 246   protected abstract unregisterWorkerMessageListener (
 247     port: Worker,
 248     listener: (message: MessageValue<Response>) => void
 249   ): void
 250
 251   protected internalExecute (
 252     worker: Worker,
 253     messageId: number
 254   ): Promise<Response> {
 255     return new Promise((resolve, reject) => {
 256       const listener: (message: MessageValue<Response>) => void = message => {
 257         if (message.id === messageId) {
 258           this.unregisterWorkerMessageListener(worker, listener)
 259           this.increaseWorkersTask(worker)
 260           if (message.error) reject(message.error)
 261           else resolve(message.data as Response)
 262         }
 263       }
 264       this.registerWorkerMessageListener(worker, listener)
 265     })
 266   }
 267
 268   /**
 269    * Returns a newly created worker.
 270    */
 271   protected abstract createWorker (): Worker
 272
 273   /**
 274    * Function that can be hooked up when a worker has been newly created and moved to the workers registry.
 275    *
 276    * Can be used to update the `maxListeners` or binding the `main-worker`<->`worker` connection if not bind by default.
 277    *
 278    * @param worker The newly created worker.
 279    */
 280   protected abstract afterWorkerSetup (worker: Worker): void
 281
 282   /**
 283    * Creates a new worker for this pool and sets it up completely.
 284    *
 285    * @returns New, completely set up worker.
 286    */
 287   protected createAndSetupWorker (): Worker {
 288     const worker: Worker = this.createWorker()
 289
 290     worker.on('error', this.opts.errorHandler ?? (() => {}))
 291     worker.on('online', this.opts.onlineHandler ?? (() => {}))
 292     worker.on('exit', this.opts.exitHandler ?? (() => {}))
 293     worker.once('exit', () => this.removeWorker(worker))
 294
 295     this.workers.push(worker)
 296
 297     // Init tasks map
 298     this.tasks.set(worker, 0)
 299
 300     this.afterWorkerSetup(worker)
 301
 302     return worker
 303   }
 304 }