src/pools/selection-strategies/weighted-round-robin-worker-choice-strategy.ts

   1 import { cpus } from 'os'
   2 import type { AbstractPoolWorker } from '../abstract-pool-worker'
   3 import type { IPoolInternal } from '../pool-internal'
   4 import { AbstractWorkerChoiceStrategy } from './abstract-worker-choice-strategy'
   5 import type { RequiredStatistics } from './selection-strategies-types'
   6
   7 /**
   8  * Virtual task runtime.
   9  */
  10 type TaskRunTime = {
  11   weight: number
  12   runTime: number
  13 }
  14
  15 /**
  16  * Selects the next worker with a weighted round robin scheduling algorithm.
  17  * Loosely modeled after the weighted round robin queueing algorithm: https://en.wikipedia.org/wiki/Weighted_round_robin.
  18  *
  19  * @template Worker Type of worker which manages the strategy.
  20  * @template Data Type of data sent to the worker. This can only be serializable data.
  21  * @template Response Type of response of execution. This can only be serializable data.
  22  */
  23 export class WeightedRoundRobinWorkerChoiceStrategy<
  24   Worker extends AbstractPoolWorker,
  25   Data,
  26   Response
  27 > extends AbstractWorkerChoiceStrategy<Worker, Data, Response> {
  28   /** @inheritDoc */
  29   public requiredStatistics: RequiredStatistics = {
  30     runTime: true
  31   }
  32
  33   /**
  34    * Worker index where the previous task was submitted.
  35    */
  36   private previousWorkerIndex: number = 0
  37   /**
  38    * Worker index where the current task will be submitted.
  39    */
  40   private currentWorkerIndex: number = 0
  41   /**
  42    * Default worker weight.
  43    */
  44   private defaultWorkerWeight: number
  45   /**
  46    * Per worker virtual task runtime map.
  47    */
  48   private workersTaskRunTime: Map<Worker, TaskRunTime> = new Map<
  49     Worker,
  50     TaskRunTime
  51   >()
  52
  53   /**
  54    * Constructs a worker choice strategy that selects with a weighted round robin scheduling algorithm.
  55    *
  56    * @param pool The pool instance.
  57    */
  58   public constructor (pool: IPoolInternal<Worker, Data, Response>) {
  59     super(pool)
  60     this.defaultWorkerWeight = this.computeWorkerWeight()
  61     this.initWorkersTaskRunTime()
  62   }
  63
  64   /** @inheritDoc */
  65   public choose (): Worker {
  66     const currentWorker = this.pool.workers[this.currentWorkerIndex]
  67     if (
  68       this.isDynamicPool === true &&
  69       this.workersTaskRunTime.has(currentWorker) === false
  70     ) {
  71       this.initWorkerTaskRunTime(currentWorker)
  72     }
  73     const workerVirtualTaskRunTime =
  74       this.getWorkerVirtualTaskRunTime(currentWorker) ?? 0
  75     const workerTaskWeight =
  76       this.workersTaskRunTime.get(currentWorker)?.weight ??
  77       this.defaultWorkerWeight
  78     if (this.currentWorkerIndex === this.previousWorkerIndex) {
  79       const workerTaskRunTime =
  80         (this.workersTaskRunTime.get(currentWorker)?.runTime ?? 0) +
  81         workerVirtualTaskRunTime
  82       this.setWorkerTaskRunTime(
  83         currentWorker,
  84         workerTaskWeight,
  85         workerTaskRunTime
  86       )
  87     } else {
  88       this.setWorkerTaskRunTime(currentWorker, workerTaskWeight, 0)
  89     }
  90     if (workerVirtualTaskRunTime < workerTaskWeight) {
  91       this.previousWorkerIndex = this.currentWorkerIndex
  92     } else {
  93       this.previousWorkerIndex = this.currentWorkerIndex
  94       this.currentWorkerIndex =
  95         this.pool.workers.length - 1 === this.currentWorkerIndex
  96           ? 0
  97           : this.currentWorkerIndex + 1
  98     }
  99     return this.pool.workers[this.currentWorkerIndex]
 100   }
 101
 102   private initWorkersTaskRunTime (): void {
 103     for (const worker of this.pool.workers) {
 104       this.initWorkerTaskRunTime(worker)
 105     }
 106   }
 107
 108   private initWorkerTaskRunTime (worker: Worker): void {
 109     this.setWorkerTaskRunTime(worker, this.defaultWorkerWeight, 0)
 110   }
 111
 112   private setWorkerTaskRunTime (
 113     worker: Worker,
 114     weight: number,
 115     runTime: number
 116   ): void {
 117     this.workersTaskRunTime.set(worker, {
 118       weight,
 119       runTime
 120     })
 121   }
 122
 123   private getWorkerVirtualTaskRunTime (worker: Worker): number | undefined {
 124     return this.pool.getWorkerAverageTasksRunTime(worker)
 125   }
 126
 127   private computeWorkerWeight (): number {
 128     let cpusCycleTimeWeight = 0
 129     for (const cpu of cpus()) {
 130       // CPU estimated cycle time
 131       const numberOfDigit = cpu.speed.toString().length - 1
 132       const cpuCycleTime = 1 / (cpu.speed / Math.pow(10, numberOfDigit))
 133       cpusCycleTimeWeight += cpuCycleTime * Math.pow(10, numberOfDigit)
 134     }
 135     return Math.round(cpusCycleTimeWeight / cpus().length)
 136   }
 137 }