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

   1 import { cpus } from 'os'
   2 import type { IPoolInternal } from '../pool-internal'
   3 import type { IPoolWorker } from '../pool-worker'
   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 IPoolWorker,
  25   Data,
  26   Response
  27 > extends AbstractWorkerChoiceStrategy<Worker, Data, Response> {
  28   /** @inheritDoc */
  29   public readonly 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 readonly defaultWorkerWeight: number
  45   /**
  46    * Per worker virtual task runtime map.
  47    */
  48   private readonly 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 reset (): boolean {
  66     this.previousWorkerIndex = 0
  67     this.currentWorkerIndex = 0
  68     this.workersTaskRunTime.clear()
  69     this.initWorkersTaskRunTime()
  70     return true
  71   }
  72
  73   /** @inheritDoc */
  74   public choose (): Worker {
  75     const currentWorker = this.pool.workers[this.currentWorkerIndex]
  76     if (
  77       this.isDynamicPool === true &&
  78       this.workersTaskRunTime.has(currentWorker) === false
  79     ) {
  80       this.initWorkerTaskRunTime(currentWorker)
  81     }
  82     const workerVirtualTaskRunTime =
  83       this.getWorkerVirtualTaskRunTime(currentWorker) ?? 0
  84     const workerTaskWeight =
  85       this.workersTaskRunTime.get(currentWorker)?.weight ??
  86       this.defaultWorkerWeight
  87     if (this.currentWorkerIndex === this.previousWorkerIndex) {
  88       const workerTaskRunTime =
  89         (this.workersTaskRunTime.get(currentWorker)?.runTime ?? 0) +
  90         workerVirtualTaskRunTime
  91       this.setWorkerTaskRunTime(
  92         currentWorker,
  93         workerTaskWeight,
  94         workerTaskRunTime
  95       )
  96     } else {
  97       this.setWorkerTaskRunTime(currentWorker, workerTaskWeight, 0)
  98     }
  99     if (workerVirtualTaskRunTime < workerTaskWeight) {
 100       this.previousWorkerIndex = this.currentWorkerIndex
 101     } else {
 102       this.previousWorkerIndex = this.currentWorkerIndex
 103       this.currentWorkerIndex =
 104         this.pool.workers.length - 1 === this.currentWorkerIndex
 105           ? 0
 106           : this.currentWorkerIndex + 1
 107     }
 108     return this.pool.workers[this.currentWorkerIndex]
 109   }
 110
 111   private initWorkersTaskRunTime (): void {
 112     for (const worker of this.pool.workers) {
 113       this.initWorkerTaskRunTime(worker)
 114     }
 115   }
 116
 117   private initWorkerTaskRunTime (worker: Worker): void {
 118     this.setWorkerTaskRunTime(worker, this.defaultWorkerWeight, 0)
 119   }
 120
 121   private setWorkerTaskRunTime (
 122     worker: Worker,
 123     weight: number,
 124     runTime: number
 125   ): void {
 126     this.workersTaskRunTime.set(worker, {
 127       weight,
 128       runTime
 129     })
 130   }
 131
 132   private getWorkerVirtualTaskRunTime (worker: Worker): number | undefined {
 133     return this.pool.getWorkerAverageTasksRunTime(worker)
 134   }
 135
 136   private computeWorkerWeight (): number {
 137     let cpusCycleTimeWeight = 0
 138     for (const cpu of cpus()) {
 139       // CPU estimated cycle time
 140       const numberOfDigit = cpu.speed.toString().length - 1
 141       const cpuCycleTime = 1 / (cpu.speed / Math.pow(10, numberOfDigit))
 142       cpusCycleTimeWeight += cpuCycleTime * Math.pow(10, numberOfDigit)
 143     }
 144     return Math.round(cpusCycleTimeWeight / cpus().length)
 145   }
 146 }