docs: refine README.md

[poolifier.git] / src / pools / selection-strategies / weighted-round-robin-worker-choice-strategy.ts

import { cpus } from 'node:os'
import type { IWorker } from '../worker'
import type { IPool } from '../pool'
import { DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS } from '../../utils'
import { AbstractWorkerChoiceStrategy } from './abstract-worker-choice-strategy'
import type {
  IWorkerChoiceStrategy,
  RequiredStatistics,
  WorkerChoiceStrategyOptions
} from './selection-strategies-types'

/**
 * Selects the next worker with a weighted round robin scheduling algorithm.
 * Loosely modeled after the weighted round robin queueing algorithm: https://en.wikipedia.org/wiki/Weighted_round_robin.
 *
 * @typeParam Worker - Type of worker which manages the strategy.
 * @typeParam Data - Type of data sent to the worker. This can only be serializable data.
 * @typeParam Response - Type of execution response. This can only be serializable data.
 */
export class WeightedRoundRobinWorkerChoiceStrategy<
    Worker extends IWorker,
    Data = unknown,
    Response = unknown
  >
  extends AbstractWorkerChoiceStrategy<Worker, Data, Response>
  implements IWorkerChoiceStrategy {
  /** @inheritDoc */
  public readonly requiredStatistics: RequiredStatistics = {
    runTime: true,
    avgRunTime: true,
    medRunTime: false
  }

  /**
   * Worker node id where the current task will be submitted.
   */
  private currentWorkerNodeId: number = 0
  /**
   * Default worker weight.
   */
  private readonly defaultWorkerWeight: number
  /**
   * Worker virtual task runtime.
   */
  private workerVirtualTaskRunTime: number = 0

  /** @inheritDoc */
  public constructor (
    pool: IPool<Worker, Data, Response>,
    opts: WorkerChoiceStrategyOptions = DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS
  ) {
    super(pool, opts)
    this.checkOptions(this.opts)
    this.defaultWorkerWeight = this.computeDefaultWorkerWeight()
  }

  /** @inheritDoc */
  public reset (): boolean {
    this.currentWorkerNodeId = 0
    this.workerVirtualTaskRunTime = 0
    return true
  }

  /** @inheritDoc */
  public choose (): number {
    const chosenWorkerNodeKey = this.currentWorkerNodeId
    const workerVirtualTaskRunTime = this.workerVirtualTaskRunTime ?? 0
    const workerTaskWeight =
      this.opts.weights?.[chosenWorkerNodeKey] ?? this.defaultWorkerWeight
    if (workerVirtualTaskRunTime < workerTaskWeight) {
      this.workerVirtualTaskRunTime =
        workerVirtualTaskRunTime +
        (this.getWorkerVirtualTaskRunTime(chosenWorkerNodeKey) ?? 0)
    } else {
      this.currentWorkerNodeId =
        this.currentWorkerNodeId === this.pool.workerNodes.length - 1
          ? 0
          : this.currentWorkerNodeId + 1
      this.workerVirtualTaskRunTime = 0
    }
    return chosenWorkerNodeKey
  }

  /** @inheritDoc */
  public remove (workerNodeKey: number): boolean {
    if (this.currentWorkerNodeId === workerNodeKey) {
      if (this.pool.workerNodes.length === 0) {
        this.currentWorkerNodeId = 0
      } else {
        this.currentWorkerNodeId =
          this.currentWorkerNodeId > this.pool.workerNodes.length - 1
            ? this.pool.workerNodes.length - 1
            : this.currentWorkerNodeId
      }
      this.workerVirtualTaskRunTime = 0
    }
    return true
  }

  private getWorkerVirtualTaskRunTime (workerNodeKey: number): number {
    return this.requiredStatistics.medRunTime
      ? this.pool.workerNodes[workerNodeKey].tasksUsage.medRunTime
      : this.pool.workerNodes[workerNodeKey].tasksUsage.avgRunTime
  }

  private computeDefaultWorkerWeight (): number {
    let cpusCycleTimeWeight = 0
    for (const cpu of cpus()) {
      // CPU estimated cycle time
      const numberOfDigits = cpu.speed.toString().length - 1
      const cpuCycleTime = 1 / (cpu.speed / Math.pow(10, numberOfDigits))
      cpusCycleTimeWeight += cpuCycleTime * Math.pow(10, numberOfDigits)
    }
    return Math.round(cpusCycleTimeWeight / cpus().length)
  }
}