perf: remove unneeded branching in worker choice strategies

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

import type { IPool } from '../pool.js'
import type { IWorker } from '../worker.js'
import { AbstractWorkerChoiceStrategy } from './abstract-worker-choice-strategy.js'
import {
  type IWorkerChoiceStrategy,
  Measurements,
  type TaskStatisticsRequirements,
  type WorkerChoiceStrategyOptions
} from './selection-strategies-types.js'

/**
 * 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 structured-cloneable data.
 * @typeParam Response - Type of execution response. This can only be structured-cloneable data.
 */
export class FairShareWorkerChoiceStrategy<
    Worker extends IWorker,
    Data = unknown,
    Response = unknown
  >
  extends AbstractWorkerChoiceStrategy<Worker, Data, Response>
  implements IWorkerChoiceStrategy {
  /** @inheritDoc */
  public readonly taskStatisticsRequirements: TaskStatisticsRequirements = {
    runTime: {
      aggregate: true,
      average: true,
      median: false
    },
    waitTime: {
      aggregate: true,
      average: true,
      median: false
    },
    elu: {
      aggregate: true,
      average: true,
      median: false
    }
  }

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

  /** @inheritDoc */
  public reset (): boolean {
    for (const workerNode of this.pool.workerNodes) {
      delete workerNode.strategyData?.virtualTaskEndTimestamp
    }
    return true
  }

  /** @inheritDoc */
  public update (workerNodeKey: number): boolean {
    this.pool.workerNodes[workerNodeKey].strategyData = {
      virtualTaskEndTimestamp:
        this.computeWorkerNodeVirtualTaskEndTimestamp(workerNodeKey)
    }
    return true
  }

  /** @inheritDoc */
  public choose (): number | undefined {
    this.setPreviousWorkerNodeKey(this.nextWorkerNodeKey)
    this.nextWorkerNodeKey = this.fairShareNextWorkerNodeKey()
    return this.nextWorkerNodeKey
  }

  /** @inheritDoc */
  public remove (): boolean {
    return true
  }

  private fairShareNextWorkerNodeKey (): number | undefined {
    return this.pool.workerNodes.reduce(
      (minWorkerNodeKey, workerNode, workerNodeKey, workerNodes) => {
        if (workerNode.strategyData?.virtualTaskEndTimestamp == null) {
          workerNode.strategyData = {
            virtualTaskEndTimestamp:
              this.computeWorkerNodeVirtualTaskEndTimestamp(workerNodeKey)
          }
        }
        return this.isWorkerNodeReady(workerNodeKey) &&
          // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
          workerNode.strategyData.virtualTaskEndTimestamp! <
            // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
            workerNodes[minWorkerNodeKey].strategyData!.virtualTaskEndTimestamp!
          ? workerNodeKey
          : minWorkerNodeKey
      },
      0
    )
  }

  /**
   * Computes the worker node key virtual task end timestamp.
   *
   * @param workerNodeKey - The worker node key.
   * @returns The worker node key virtual task end timestamp.
   */
  private computeWorkerNodeVirtualTaskEndTimestamp (
    workerNodeKey: number
  ): number {
    return this.getWorkerNodeVirtualTaskEndTimestamp(
      workerNodeKey,
      this.getWorkerNodeVirtualTaskStartTimestamp(workerNodeKey)
    )
  }

  private getWorkerNodeVirtualTaskEndTimestamp (
    workerNodeKey: number,
    workerNodeVirtualTaskStartTimestamp: number
  ): number {
    const workerNodeTaskExecutionTime =
      this.getWorkerNodeTaskWaitTime(workerNodeKey) +
      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
      (this.opts!.measurement === Measurements.elu
        ? this.getWorkerNodeTaskElu(workerNodeKey)
        : this.getWorkerNodeTaskRunTime(workerNodeKey))
    return workerNodeVirtualTaskStartTimestamp + workerNodeTaskExecutionTime
  }

  private getWorkerNodeVirtualTaskStartTimestamp (
    workerNodeKey: number
  ): number {
    const virtualTaskEndTimestamp =
      this.pool.workerNodes[workerNodeKey]?.strategyData
        ?.virtualTaskEndTimestamp
    const now = performance.now()
    return now < (virtualTaskEndTimestamp ?? -Infinity)
      ? // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
      virtualTaskEndTimestamp!
      : now
  }
}