feat: add custom worker weights to worker choice strategies options

[poolifier.git] / src / pools / selection-strategies / fair-share-worker-choice-strategy.ts

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

/**
 * Worker virtual task timestamp.
 */
interface WorkerVirtualTaskTimestamp {
  start: number
  end: number
}

/**
 * Selects the next worker with a fair share scheduling algorithm.
 * Loosely modeled after the fair queueing algorithm: https://en.wikipedia.org/wiki/Fair_queuing.
 *
 * @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 FairShareWorkerChoiceStrategy<
    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
  }

  /**
   * Workers' virtual task execution timestamp.
   */
  private workersVirtualTaskTimestamp: WorkerVirtualTaskTimestamp[] = []

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

  /** @inheritDoc */
  public reset (): boolean {
    this.workersVirtualTaskTimestamp = []
    return true
  }

  /** @inheritDoc */
  public choose (): number {
    let minWorkerVirtualTaskEndTimestamp = Infinity
    let chosenWorkerNodeKey!: number
    for (const [workerNodeKey] of this.pool.workerNodes.entries()) {
      this.computeWorkerVirtualTaskTimestamp(workerNodeKey)
      const workerLastVirtualTaskEndTimestamp =
        this.workersVirtualTaskTimestamp[workerNodeKey]?.end ?? 0
      if (
        workerLastVirtualTaskEndTimestamp < minWorkerVirtualTaskEndTimestamp
      ) {
        minWorkerVirtualTaskEndTimestamp = workerLastVirtualTaskEndTimestamp
        chosenWorkerNodeKey = workerNodeKey
      }
    }
    return chosenWorkerNodeKey
  }

  /** @inheritDoc */
  public remove (workerNodeKey: number): boolean {
    this.workersVirtualTaskTimestamp.splice(workerNodeKey, 1)
    return true
  }

  /**
   * Computes worker virtual task timestamp.
   *
   * @param workerNodeKey - The worker node key.
   */
  private computeWorkerVirtualTaskTimestamp (workerNodeKey: number): void {
    const workerVirtualTaskStartTimestamp = Math.max(
      performance.now(),
      this.workersVirtualTaskTimestamp[workerNodeKey]?.end ?? -Infinity
    )
    const workerVirtualTaskTRunTime = this.requiredStatistics.medRunTime
      ? this.pool.workerNodes[workerNodeKey].tasksUsage.medRunTime
      : this.pool.workerNodes[workerNodeKey].tasksUsage.avgRunTime
    this.workersVirtualTaskTimestamp[workerNodeKey] = {
      start: workerVirtualTaskStartTimestamp,
      end: workerVirtualTaskStartTimestamp + (workerVirtualTaskTRunTime ?? 0)
    }
  }
}