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