src/pools/selection-strategies/fair-share-worker-choice-strategy.ts

   1 import { DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS } from '../../utils'
   2 import type { IPool } from '../pool'
   3 import type { IWorker } from '../worker'
   4 import { AbstractWorkerChoiceStrategy } from './abstract-worker-choice-strategy'
   5 import type {
   6   IWorkerChoiceStrategy,
   7   TaskStatisticsRequirements,
   8   WorkerChoiceStrategyOptions
   9 } from './selection-strategies-types'
  10
  11 /**
  12  * Selects the next worker with a fair share scheduling algorithm.
  13  * Loosely modeled after the fair queueing algorithm: https://en.wikipedia.org/wiki/Fair_queuing.
  14  *
  15  * @typeParam Worker - Type of worker which manages the strategy.
  16  * @typeParam Data - Type of data sent to the worker. This can only be serializable data.
  17  * @typeParam Response - Type of execution response. This can only be serializable data.
  18  */
  19 export class FairShareWorkerChoiceStrategy<
  20     Worker extends IWorker,
  21     Data = unknown,
  22     Response = unknown
  23   >
  24   extends AbstractWorkerChoiceStrategy<Worker, Data, Response>
  25   implements IWorkerChoiceStrategy {
  26   /** @inheritDoc */
  27   public readonly taskStatisticsRequirements: TaskStatisticsRequirements = {
  28     runTime: {
  29       aggregate: true,
  30       average: true,
  31       median: false
  32     },
  33     waitTime: {
  34       aggregate: false,
  35       average: false,
  36       median: false
  37     },
  38     elu: false
  39   }
  40
  41   /**
  42    * Workers' virtual task end execution timestamp.
  43    */
  44   private workersVirtualTaskEndTimestamp: number[] = []
  45
  46   /** @inheritDoc */
  47   public constructor (
  48     pool: IPool<Worker, Data, Response>,
  49     opts: WorkerChoiceStrategyOptions = DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS
  50   ) {
  51     super(pool, opts)
  52     this.setTaskStatisticsRequirements(this.opts)
  53   }
  54
  55   /** @inheritDoc */
  56   public reset (): boolean {
  57     this.workersVirtualTaskEndTimestamp = []
  58     return true
  59   }
  60
  61   /** @inheritDoc */
  62   public update (workerNodeKey: number): boolean {
  63     this.computeWorkerVirtualTaskEndTimestamp(workerNodeKey)
  64     return true
  65   }
  66
  67   /** @inheritDoc */
  68   public choose (): number {
  69     let minWorkerVirtualTaskEndTimestamp = Infinity
  70     let chosenWorkerNodeKey!: number
  71     for (const [workerNodeKey] of this.pool.workerNodes.entries()) {
  72       if (this.workersVirtualTaskEndTimestamp[workerNodeKey] == null) {
  73         this.computeWorkerVirtualTaskEndTimestamp(workerNodeKey)
  74       }
  75       const workerVirtualTaskEndTimestamp =
  76         this.workersVirtualTaskEndTimestamp[workerNodeKey]
  77       if (workerVirtualTaskEndTimestamp < minWorkerVirtualTaskEndTimestamp) {
  78         minWorkerVirtualTaskEndTimestamp = workerVirtualTaskEndTimestamp
  79         chosenWorkerNodeKey = workerNodeKey
  80       }
  81     }
  82     return chosenWorkerNodeKey
  83   }
  84
  85   /** @inheritDoc */
  86   public remove (workerNodeKey: number): boolean {
  87     this.workersVirtualTaskEndTimestamp.splice(workerNodeKey, 1)
  88     return true
  89   }
  90
  91   /**
  92    * Computes the worker node key virtual task end timestamp.
  93    *
  94    * @param workerNodeKey - The worker node key.
  95    */
  96   private computeWorkerVirtualTaskEndTimestamp (workerNodeKey: number): void {
  97     this.workersVirtualTaskEndTimestamp[workerNodeKey] =
  98       this.getWorkerVirtualTaskEndTimestamp(
  99         workerNodeKey,
 100         this.getWorkerVirtualTaskStartTimestamp(workerNodeKey)
 101       )
 102   }
 103
 104   private getWorkerVirtualTaskEndTimestamp (
 105     workerNodeKey: number,
 106     workerVirtualTaskStartTimestamp: number
 107   ): number {
 108     return (
 109       workerVirtualTaskStartTimestamp + this.getWorkerTaskRunTime(workerNodeKey)
 110     )
 111   }
 112
 113   private getWorkerVirtualTaskStartTimestamp (workerNodeKey: number): number {
 114     return Math.max(
 115       performance.now(),
 116       this.workersVirtualTaskEndTimestamp[workerNodeKey] ?? -Infinity
 117     )
 118   }
 119 }