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  * @typeParam Worker - Type of worker which manages the strategy.
  20  * @typeParam Data - Type of data sent to the worker. This can only be serializable data.
  21  * @typeParam 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 id where the current task will be submitted.
  35    */
  36   private currentWorkerId: 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.currentWorkerId = 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.get(this.currentWorkerId)
  71       ?.worker as Worker
  72     if (this.isDynamicPool && !this.workersTaskRunTime.has(chosenWorker)) {
  73       this.initWorkerTaskRunTime(chosenWorker)
  74     }
  75     const workerTaskRunTime =
  76       this.workersTaskRunTime.get(chosenWorker)?.runTime ?? 0
  77     const workerTaskWeight =
  78       this.workersTaskRunTime.get(chosenWorker)?.weight ??
  79       this.defaultWorkerWeight
  80     if (workerTaskRunTime < workerTaskWeight) {
  81       this.setWorkerTaskRunTime(
  82         chosenWorker,
  83         workerTaskWeight,
  84         workerTaskRunTime +
  85           (this.getWorkerVirtualTaskRunTime(chosenWorker) ?? 0)
  86       )
  87     } else {
  88       this.currentWorkerId =
  89         this.currentWorkerId === this.pool.workers.size - 1
  90           ? 0
  91           : this.currentWorkerId + 1
  92       this.setWorkerTaskRunTime(
  93         this.pool.workers.get(this.currentWorkerId)?.worker as Worker,
  94         workerTaskWeight,
  95         0
  96       )
  97     }
  98     return chosenWorker
  99   }
 100
 101   private initWorkersTaskRunTime (): void {
 102     for (const value of this.pool.workers.values()) {
 103       this.initWorkerTaskRunTime(value.worker)
 104     }
 105   }
 106
 107   private initWorkerTaskRunTime (worker: Worker): void {
 108     this.setWorkerTaskRunTime(worker, this.defaultWorkerWeight, 0)
 109   }
 110
 111   private setWorkerTaskRunTime (
 112     worker: Worker,
 113     weight: number,
 114     runTime: number
 115   ): void {
 116     this.workersTaskRunTime.set(worker, {
 117       weight,
 118       runTime
 119     })
 120   }
 121
 122   private getWorkerVirtualTaskRunTime (worker: Worker): number | undefined {
 123     return this.pool.getWorkerAverageTasksRunTime(worker)
 124   }
 125
 126   private computeWorkerWeight (): number {
 127     let cpusCycleTimeWeight = 0
 128     for (const cpu of cpus()) {
 129       // CPU estimated cycle time
 130       const numberOfDigits = cpu.speed.toString().length - 1
 131       const cpuCycleTime = 1 / (cpu.speed / Math.pow(10, numberOfDigits))
 132       cpusCycleTimeWeight += cpuCycleTime * Math.pow(10, numberOfDigits)
 133     }
 134     return Math.round(cpusCycleTimeWeight / cpus().length)
 135   }
 136 }