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 numberOfWorkers 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 numberOfWorkers: 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.numberOfWorkers; i++) {
 126       this.internalNewWorker()
 127     }
 128
 129     this.emitter = new PoolEmitter()
 130   }
 131
 132   /**
 133    * Number of workers that this pool should manage.
 134    *
 135    * @returns Number of workers that this pool manages.
 136    * @deprecated Only here for backward compatibility.
 137    */
 138   // eslint-disable-next-line spellcheck/spell-checker
 139   public get numWorkers (): number {
 140     return this.numberOfWorkers
 141   }
 142
 143   /**
 144    * Setup hook that can be overridden by a Poolifier pool implementation
 145    * to run code before workers are created in the abstract constructor.
 146    */
 147   protected setupHook (): void {
 148     // Can be overridden
 149   }
 150
 151   /**
 152    * Should return whether the worker is the main worker or not.
 153    */
 154   protected abstract isMain (): boolean
 155
 156   public async destroy (): Promise<void> {
 157     for (const worker of this.workers) {
 158       await this.destroyWorker(worker)
 159     }
 160   }
 161
 162   /**
 163    * Shut down given worker.
 164    *
 165    * @param worker A worker within `workers`.
 166    */
 167   protected abstract destroyWorker (worker: Worker): void | Promise<void>
 168
 169   /**
 170    * Send a message to the given worker.
 171    *
 172    * @param worker The worker which should receive the message.
 173    * @param message The message.
 174    */
 175   protected abstract sendToWorker (
 176     worker: Worker,
 177     message: MessageValue<Data>
 178   ): void
 179
 180   /**
 181    * Adds the given worker to the pool.
 182    *
 183    * @param worker Worker that will be added.
 184    */
 185   protected addWorker (worker: Worker): void {
 186     const previousWorkerIndex = this.tasks.get(worker)
 187     if (previousWorkerIndex !== undefined) {
 188       this.tasks.set(worker, previousWorkerIndex + 1)
 189     } else {
 190       throw Error('Worker could not be found in tasks map')
 191     }
 192   }
 193
 194   /**
 195    * Removes the given worker from the pool.
 196    *
 197    * @param worker Worker that will be removed.
 198    */
 199   protected removeWorker (worker: Worker): void {
 200     // Clean worker from data structure
 201     const workerIndex = this.workers.indexOf(worker)
 202     this.workers.splice(workerIndex, 1)
 203     this.tasks.delete(worker)
 204   }
 205
 206   public execute (data: Data): Promise<Response> {
 207     // Configure worker to handle message with the specified task
 208     const worker = this.chooseWorker()
 209     this.addWorker(worker)
 210     const id = ++this.id
 211     const res = this.internalExecute(worker, id)
 212     this.sendToWorker(worker, { data: data || ({} as Data), id: id })
 213     return res
 214   }
 215
 216   protected abstract registerWorkerMessageListener (
 217     port: Worker,
 218     listener: (message: MessageValue<Response>) => void
 219   ): void
 220
 221   protected abstract unregisterWorkerMessageListener (
 222     port: Worker,
 223     listener: (message: MessageValue<Response>) => void
 224   ): void
 225
 226   protected internalExecute (worker: Worker, id: number): Promise<Response> {
 227     return new Promise((resolve, reject) => {
 228       const listener: (message: MessageValue<Response>) => void = message => {
 229         if (message.id === id) {
 230           this.unregisterWorkerMessageListener(worker, listener)
 231           this.addWorker(worker)
 232           if (message.error) reject(message.error)
 233           else resolve(message.data as Response)
 234         }
 235       }
 236       this.registerWorkerMessageListener(worker, listener)
 237     })
 238   }
 239
 240   /**
 241    * Choose a worker for the next task.
 242    *
 243    * The default implementation uses a round robin algorithm to distribute the load.
 244    *
 245    * @returns Worker.
 246    */
 247   protected chooseWorker (): Worker {
 248     this.nextWorker =
 249       this.nextWorker === this.workers.length - 1 ? 0 : this.nextWorker + 1
 250     return this.workers[this.nextWorker]
 251   }
 252
 253   /**
 254    * Returns a newly created worker.
 255    */
 256   protected abstract newWorker (): Worker
 257
 258   /**
 259    * Function that can be hooked up when a worker has been newly created and moved to the workers registry.
 260    *
 261    * Can be used to update the `maxListeners` or binding the `main-worker`<->`worker` connection if not bind by default.
 262    *
 263    * @param worker The newly created worker.
 264    */
 265   protected abstract afterNewWorkerPushed (worker: Worker): void
 266
 267   /**
 268    * Creates a new worker for this pool and sets it up completely.
 269    *
 270    * @returns New, completely set up worker.
 271    */
 272   protected internalNewWorker (): Worker {
 273     const worker: Worker = this.newWorker()
 274     worker.on('error', this.opts.errorHandler ?? (() => {}))
 275     worker.on('online', this.opts.onlineHandler ?? (() => {}))
 276     // TODO handle properly when a worker exit
 277     worker.on('exit', this.opts.exitHandler ?? (() => {}))
 278     this.workers.push(worker)
 279     this.afterNewWorkerPushed(worker)
 280     // init tasks map
 281     this.tasks.set(worker, 0)
 282     return worker
 283   }
 284 }