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 interface 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 current task will be submitted.
  35    */
  36   private currentWorkerIndex: number = 0
  37   /**
  38    * Default worker weight.
  39    */
  40   private readonly defaultWorkerWeight: number
  41   /**
  42    * Per worker virtual task runtime map.
  43    */
  44   private readonly workersTaskRunTime: Map<Worker, TaskRunTime> = new Map<
  45   Worker,
  46   TaskRunTime
  47   >()
  48
  49   /**
  50    * Constructs a worker choice strategy that selects with a weighted round robin scheduling algorithm.
  51    *
  52    * @param pool The pool instance.
  53    */
  54   public constructor (pool: IPoolInternal<Worker, Data, Response>) {
  55     super(pool)
  56     this.defaultWorkerWeight = this.computeWorkerWeight()
  57     this.initWorkersTaskRunTime()
  58   }
  59
  60   /** @inheritDoc */
  61   public reset (): boolean {
  62     this.currentWorkerIndex = 0
  63     this.workersTaskRunTime.clear()
  64     this.initWorkersTaskRunTime()
  65     return true
  66   }
  67
  68   /** @inheritDoc */
  69   public choose (): Worker {
  70     const chosenWorker = this.pool.workers[this.currentWorkerIndex]
  71     if (this.isDynamicPool && !this.workersTaskRunTime.has(chosenWorker)) {
  72       this.initWorkerTaskRunTime(chosenWorker)
  73     }
  74     const workerTaskRunTime =
  75       this.workersTaskRunTime.get(chosenWorker)?.runTime ?? 0
  76     const workerTaskWeight =
  77       this.workersTaskRunTime.get(chosenWorker)?.weight ??
  78       this.defaultWorkerWeight
  79     if (workerTaskRunTime < workerTaskWeight) {
  80       this.setWorkerTaskRunTime(
  81         chosenWorker,
  82         workerTaskWeight,
  83         workerTaskRunTime +
  84           (this.getWorkerVirtualTaskRunTime(chosenWorker) ?? 0)
  85       )
  86     } else {
  87       this.currentWorkerIndex =
  88         this.currentWorkerIndex === this.pool.workers.length - 1
  89           ? 0
  90           : this.currentWorkerIndex + 1
  91       this.setWorkerTaskRunTime(
  92         this.pool.workers[this.currentWorkerIndex],
  93         workerTaskWeight,
  94         0
  95       )
  96     }
  97     return chosenWorker
  98   }
  99
 100   private initWorkersTaskRunTime (): void {
 101     for (const worker of this.pool.workers) {
 102       this.initWorkerTaskRunTime(worker)
 103     }
 104   }
 105
 106   private initWorkerTaskRunTime (worker: Worker): void {
 107     this.setWorkerTaskRunTime(worker, this.defaultWorkerWeight, 0)
 108   }
 109
 110   private setWorkerTaskRunTime (
 111     worker: Worker,
 112     weight: number,
 113     runTime: number
 114   ): void {
 115     this.workersTaskRunTime.set(worker, {
 116       weight,
 117       runTime
 118     })
 119   }
 120
 121   private getWorkerVirtualTaskRunTime (worker: Worker): number | undefined {
 122     return this.pool.getWorkerAverageTasksRunTime(worker)
 123   }
 124
 125   private computeWorkerWeight (): number {
 126     let cpusCycleTimeWeight = 0
 127     for (const cpu of cpus()) {
 128       // CPU estimated cycle time
 129       const numberOfDigits = cpu.speed.toString().length - 1
 130       const cpuCycleTime = 1 / (cpu.speed / Math.pow(10, numberOfDigits))
 131       cpusCycleTimeWeight += cpuCycleTime * Math.pow(10, numberOfDigits)
 132     }
 133     return Math.round(cpusCycleTimeWeight / cpus().length)
 134   }
 135 }