X-Git-Url: https://git.piment-noir.org/?a=blobdiff_plain;f=src%2Fpools%2Fabstract-pool.ts;h=c951c6f23792ea631b8804e11c7ff25719ce5fa5;hb=c319c66bad0611acf6087950a1f8a20f8124167b;hp=0763f04f9c21869e46b20414f4c998a03ad76bce;hpb=729c563db85562dd7d0f7733b1a3e2d98467134b;p=poolifier.git

diff --git a/src/pools/abstract-pool.ts b/src/pools/abstract-pool.ts
index 0763f04f..b95d16b4 100644
--- a/src/pools/abstract-pool.ts
+++ b/src/pools/abstract-pool.ts
@@ -1,140 +1,313 @@
-import EventEmitter from 'events'
-import type { MessageValue } from '../utility-types'
-import type { IPool } from './pool'
+import crypto from 'node:crypto'
+import type { MessageValue, PromiseResponseWrapper } from '../utility-types'
+import {
+  DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS,
+  EMPTY_FUNCTION,
+  median
+} from '../utils'
+import { KillBehaviors, isKillBehavior } from '../worker/worker-options'
+import {
+  PoolEvents,
+  type IPool,
+  type PoolOptions,
+  type TasksQueueOptions,
+  PoolType
+} from './pool'
+import { PoolEmitter } from './pool'
+import type { IWorker, Task, TasksUsage, WorkerNode } from './worker'
+import {
+  WorkerChoiceStrategies,
+  type WorkerChoiceStrategy
+} from './selection-strategies/selection-strategies-types'
+import { WorkerChoiceStrategyContext } from './selection-strategies/worker-choice-strategy-context'
+import { CircularArray } from '../circular-array'
 
 /**
- * Callback invoked if the worker raised an error.
- */
-export type ErrorHandler<Worker> = (this: Worker, e: Error) => void
-
-/**
- * Callback invoked when the worker has started successfully.
+ * Base class that implements some shared logic for all poolifier pools.
+ *
+ * @typeParam Worker - Type of worker which manages this pool.
+ * @typeParam Data - Type of data sent to the worker. This can only be serializable data.
+ * @typeParam Response - Type of response of execution. This can only be serializable data.
  */
-export type OnlineHandler<Worker> = (this: Worker) => void
+export abstract class AbstractPool<
+  Worker extends IWorker,
+  Data = unknown,
+  Response = unknown
+> implements IPool<Worker, Data, Response> {
+  /** @inheritDoc */
+  public readonly workerNodes: Array<WorkerNode<Worker, Data>> = []
 
-/**
- * Callback invoked when the worker exits successfully.
- */
-export type ExitHandler<Worker> = (this: Worker, code: number) => void
+  /** @inheritDoc */
+  public readonly emitter?: PoolEmitter
 
-/**
- * Basic interface that describes the minimum required implementation of listener events for a pool-worker.
- */
-export interface IWorker {
-  on(event: 'error', handler: ErrorHandler<this>): void
-  on(event: 'online', handler: OnlineHandler<this>): void
-  on(event: 'exit', handler: ExitHandler<this>): void
-}
-
-/**
- * Options for a poolifier pool.
- */
-export interface PoolOptions<Worker> {
-  /**
-   * A function that will listen for error event on each worker.
-   */
-  errorHandler?: ErrorHandler<Worker>
   /**
-   * A function that will listen for online event on each worker.
+   * The execution response promise map.
+   *
+   * - `key`: The message id of each submitted task.
+   * - `value`: An object that contains the worker, the execution response promise resolve and reject callbacks.
+   *
+   * When we receive a message from the worker, we get a map entry with the promise resolve/reject bound to the message id.
    */
-  onlineHandler?: OnlineHandler<Worker>
+  protected promiseResponseMap: Map<
+  string,
+  PromiseResponseWrapper<Worker, Response>
+  > = new Map<string, PromiseResponseWrapper<Worker, Response>>()
+
   /**
-   * A function that will listen for exit event on each worker.
+   * Worker choice strategy context referencing a worker choice algorithm implementation.
+   *
+   * Default to a round robin algorithm.
    */
-  exitHandler?: ExitHandler<Worker>
+  protected workerChoiceStrategyContext: WorkerChoiceStrategyContext<
+  Worker,
+  Data,
+  Response
+  >
+
   /**
-   * This is just to avoid non-useful warning messages.
-   *
-   * Will be used to set `maxListeners` on event emitters (workers are event emitters).
+   * Constructs a new poolifier pool.
    *
-   * @default 1000
-   * @see [Node events emitter.setMaxListeners(n)](https://nodejs.org/api/events.html#events_emitter_setmaxlisteners_n)
+   * @param numberOfWorkers - Number of workers that this pool should manage.
+   * @param filePath - Path to the worker-file.
+   * @param opts - Options for the pool.
    */
-  maxTasks?: number
-}
+  public constructor (
+    public readonly numberOfWorkers: number,
+    public readonly filePath: string,
+    public readonly opts: PoolOptions<Worker>
+  ) {
+    if (!this.isMain()) {
+      throw new Error('Cannot start a pool from a worker!')
+    }
+    this.checkNumberOfWorkers(this.numberOfWorkers)
+    this.checkFilePath(this.filePath)
+    this.checkPoolOptions(this.opts)
 
-/**
- * Internal poolifier pool emitter.
- */
-class PoolEmitter extends EventEmitter {}
+    this.chooseWorkerNode.bind(this)
+    this.executeTask.bind(this)
+    this.enqueueTask.bind(this)
+    this.checkAndEmitEvents.bind(this)
 
-/**
- * Base class containing some shared logic for all poolifier pools.
- *
- * @template Worker Type of worker which manages this pool.
- * @template Data Type of data sent to the worker.
- * @template Response Type of response of execution.
- */
-export abstract class AbstractPool<
-  Worker extends IWorker,
-  Data = unknown,
-  Response = unknown
-> implements IPool<Data, Response> {
-  /**
-   * List of currently available workers.
-   */
-  public readonly workers: Worker[] = []
+    this.setupHook()
+
+    for (let i = 1; i <= this.numberOfWorkers; i++) {
+      this.createAndSetupWorker()
+    }
+
+    if (this.opts.enableEvents === true) {
+      this.emitter = new PoolEmitter()
+    }
+    this.workerChoiceStrategyContext = new WorkerChoiceStrategyContext<
+    Worker,
+    Data,
+    Response
+    >(
+      this,
+      this.opts.workerChoiceStrategy,
+      this.opts.workerChoiceStrategyOptions
+    )
+  }
+
+  private checkFilePath (filePath: string): void {
+    if (
+      filePath == null ||
+      (typeof filePath === 'string' && filePath.trim().length === 0)
+    ) {
+      throw new Error('Please specify a file with a worker implementation')
+    }
+  }
+
+  private checkNumberOfWorkers (numberOfWorkers: number): void {
+    if (numberOfWorkers == null) {
+      throw new Error(
+        'Cannot instantiate a pool without specifying the number of workers'
+      )
+    } else if (!Number.isSafeInteger(numberOfWorkers)) {
+      throw new TypeError(
+        'Cannot instantiate a pool with a non integer number of workers'
+      )
+    } else if (numberOfWorkers < 0) {
+      throw new RangeError(
+        'Cannot instantiate a pool with a negative number of workers'
+      )
+    } else if (this.type === PoolType.FIXED && numberOfWorkers === 0) {
+      throw new Error('Cannot instantiate a fixed pool with no worker')
+    }
+  }
+
+  private checkPoolOptions (opts: PoolOptions<Worker>): void {
+    this.opts.workerChoiceStrategy =
+      opts.workerChoiceStrategy ?? WorkerChoiceStrategies.ROUND_ROBIN
+    this.checkValidWorkerChoiceStrategy(this.opts.workerChoiceStrategy)
+    this.opts.workerChoiceStrategyOptions =
+      opts.workerChoiceStrategyOptions ?? DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS
+    this.opts.enableEvents = opts.enableEvents ?? true
+    this.opts.enableTasksQueue = opts.enableTasksQueue ?? false
+    if (this.opts.enableTasksQueue) {
+      if ((opts.tasksQueueOptions?.concurrency as number) <= 0) {
+        throw new Error(
+          `Invalid worker tasks concurrency '${
+            (opts.tasksQueueOptions as TasksQueueOptions).concurrency as number
+          }'`
+        )
+      }
+      this.opts.tasksQueueOptions = {
+        concurrency: opts.tasksQueueOptions?.concurrency ?? 1
+      }
+    }
+  }
+
+  private checkValidWorkerChoiceStrategy (
+    workerChoiceStrategy: WorkerChoiceStrategy
+  ): void {
+    if (!Object.values(WorkerChoiceStrategies).includes(workerChoiceStrategy)) {
+      throw new Error(
+        `Invalid worker choice strategy '${workerChoiceStrategy}'`
+      )
+    }
+  }
+
+  /** @inheritDoc */
+  public abstract get type (): PoolType
 
   /**
-   * ID for the next worker.
+   * Number of tasks running in the pool.
    */
-  public nextWorker: number = 0
+  private get numberOfRunningTasks (): number {
+    return this.workerNodes.reduce(
+      (accumulator, workerNode) => accumulator + workerNode.tasksUsage.running,
+      0
+    )
+  }
 
   /**
-   * - `key`: The `Worker`
-   * - `value`: Number of tasks that has been assigned to that worker since it started
+   * Number of tasks queued in the pool.
    */
-  public readonly tasks: Map<Worker, number> = new Map<Worker, number>()
+  private get numberOfQueuedTasks (): number {
+    if (this.opts.enableTasksQueue === false) {
+      return 0
+    }
+    return this.workerNodes.reduce(
+      (accumulator, workerNode) => accumulator + workerNode.tasksQueue.length,
+      0
+    )
+  }
 
   /**
-   * Emitter on which events can be listened to.
-   *
-   * Events that can currently be listened to:
+   * Gets the given worker its worker node key.
    *
-   * - `'FullPool'`
+   * @param worker - The worker.
+   * @returns The worker node key if the worker is found in the pool worker nodes, `-1` otherwise.
    */
-  public readonly emitter: PoolEmitter
+  private getWorkerNodeKey (worker: Worker): number {
+    return this.workerNodes.findIndex(
+      workerNode => workerNode.worker === worker
+    )
+  }
+
+  /** @inheritDoc */
+  public setWorkerChoiceStrategy (
+    workerChoiceStrategy: WorkerChoiceStrategy
+  ): void {
+    this.checkValidWorkerChoiceStrategy(workerChoiceStrategy)
+    this.opts.workerChoiceStrategy = workerChoiceStrategy
+    for (const workerNode of this.workerNodes) {
+      this.setWorkerNodeTasksUsage(workerNode, {
+        run: 0,
+        running: 0,
+        runTime: 0,
+        runTimeHistory: new CircularArray(),
+        avgRunTime: 0,
+        medRunTime: 0,
+        error: 0
+      })
+    }
+    this.workerChoiceStrategyContext.setWorkerChoiceStrategy(
+      workerChoiceStrategy
+    )
+  }
 
   /**
-   * ID of the next message.
+   * Whether the pool is full or not.
+   *
+   * The pool filling boolean status.
    */
-  protected id: number = 0
+  protected abstract get full (): boolean
 
   /**
-   * Constructs a new poolifier pool.
+   * Whether the pool is busy or not.
    *
-   * @param numWorkers Number of workers that this pool should manage.
-   * @param filePath Path to the worker-file.
-   * @param opts Options for the pool. Default: `{ maxTasks: 1000 }`
+   * The pool busyness boolean status.
    */
-  public constructor (
-    public readonly numWorkers: number,
-    public readonly filePath: string,
-    public readonly opts: PoolOptions<Worker> = { maxTasks: 1000 }
-  ) {
-    if (!this.isMain()) {
-      throw new Error('Cannot start a pool from a worker!')
-    }
-    // TODO christopher 2021-02-07: Improve this check e.g. with a pattern or blank check
-    if (!this.filePath) {
-      throw new Error('Please specify a file with a worker implementation')
-    }
+  protected abstract get busy (): boolean
 
-    this.setupHook()
+  protected internalBusy (): boolean {
+    return this.findFreeWorkerNodeKey() === -1
+  }
 
-    for (let i = 1; i <= this.numWorkers; i++) {
-      this.internalNewWorker()
+  /** @inheritDoc */
+  public findFreeWorkerNodeKey (): number {
+    return this.workerNodes.findIndex(workerNode => {
+      return workerNode.tasksUsage?.running === 0
+    })
+  }
+
+  /** @inheritDoc */
+  public async execute (data: Data): Promise<Response> {
+    const [workerNodeKey, workerNode] = this.chooseWorkerNode()
+    const submittedTask: Task<Data> = {
+      // eslint-disable-next-line @typescript-eslint/consistent-type-assertions
+      data: data ?? ({} as Data),
+      id: crypto.randomUUID()
+    }
+    const res = new Promise<Response>((resolve, reject) => {
+      this.promiseResponseMap.set(submittedTask.id, {
+        resolve,
+        reject,
+        worker: workerNode.worker
+      })
+    })
+    if (
+      this.opts.enableTasksQueue === true &&
+      (this.busy ||
+        this.workerNodes[workerNodeKey].tasksUsage.running >=
+          ((this.opts.tasksQueueOptions as TasksQueueOptions)
+            .concurrency as number))
+    ) {
+      this.enqueueTask(workerNodeKey, submittedTask)
+    } else {
+      this.executeTask(workerNodeKey, submittedTask)
     }
+    this.checkAndEmitEvents()
+    // eslint-disable-next-line @typescript-eslint/return-await
+    return res
+  }
 
-    this.emitter = new PoolEmitter()
+  /** @inheritDoc */
+  public async destroy (): Promise<void> {
+    await Promise.all(
+      this.workerNodes.map(async (workerNode, workerNodeKey) => {
+        this.flushTasksQueue(workerNodeKey)
+        await this.destroyWorker(workerNode.worker)
+      })
+    )
   }
 
   /**
-   * Setup hook that can be overridden by a Poolifer pool implementation
-   * to run code before workers are created in the abstract constructor.
+   * Shutdowns the given worker.
+   *
+   * @param worker - A worker within `workerNodes`.
+   */
+  protected abstract destroyWorker (worker: Worker): void | Promise<void>
+
+  /**
+   * Setup hook to execute code before worker node are created in the abstract constructor.
+   * Can be overridden
+   *
+   * @virtual
    */
   protected setupHook (): void {
-    // Can be overridden
+    // Intentionally empty
   }
 
   /**
@@ -142,24 +315,83 @@ export abstract class AbstractPool<
    */
   protected abstract isMain (): boolean
 
-  public async destroy (): Promise<void> {
-    for (const worker of this.workers) {
-      await this.destroyWorker(worker)
+  /**
+   * Hook executed before the worker task execution.
+   * Can be overridden.
+   *
+   * @param workerNodeKey - The worker node key.
+   */
+  protected beforeTaskExecutionHook (workerNodeKey: number): void {
+    ++this.workerNodes[workerNodeKey].tasksUsage.running
+  }
+
+  /**
+   * Hook executed after the worker task execution.
+   * Can be overridden.
+   *
+   * @param worker - The worker.
+   * @param message - The received message.
+   */
+  protected afterTaskExecutionHook (
+    worker: Worker,
+    message: MessageValue<Response>
+  ): void {
+    const workerTasksUsage = this.getWorkerTasksUsage(worker) as TasksUsage
+    --workerTasksUsage.running
+    ++workerTasksUsage.run
+    if (message.error != null) {
+      ++workerTasksUsage.error
+    }
+    if (this.workerChoiceStrategyContext.getRequiredStatistics().runTime) {
+      workerTasksUsage.runTime += message.runTime ?? 0
+      if (
+        this.workerChoiceStrategyContext.getRequiredStatistics().avgRunTime &&
+        workerTasksUsage.run !== 0
+      ) {
+        workerTasksUsage.avgRunTime =
+          workerTasksUsage.runTime / workerTasksUsage.run
+      }
+      if (this.workerChoiceStrategyContext.getRequiredStatistics().medRunTime) {
+        workerTasksUsage.runTimeHistory.push(message.runTime ?? 0)
+        workerTasksUsage.medRunTime = median(workerTasksUsage.runTimeHistory)
+      }
     }
   }
 
   /**
-   * Shut down given worker.
+   * Chooses a worker node for the next task.
+   *
+   * The default uses a round robin algorithm to distribute the load.
    *
-   * @param worker A worker within `workers`.
+   * @returns [worker node key, worker node].
    */
-  protected abstract destroyWorker (worker: Worker): void | Promise<void>
+  protected chooseWorkerNode (): [number, WorkerNode<Worker, Data>] {
+    let workerNodeKey: number
+    if (this.type === PoolType.DYNAMIC && !this.full && this.internalBusy()) {
+      const workerCreated = this.createAndSetupWorker()
+      this.registerWorkerMessageListener(workerCreated, message => {
+        if (
+          isKillBehavior(KillBehaviors.HARD, message.kill) ||
+          (message.kill != null &&
+            this.getWorkerTasksUsage(workerCreated)?.running === 0)
+        ) {
+          // Kill message received from the worker: no new tasks are submitted to that worker for a while ( > maxInactiveTime)
+          this.flushTasksQueueByWorker(workerCreated)
+          void this.destroyWorker(workerCreated)
+        }
+      })
+      workerNodeKey = this.getWorkerNodeKey(workerCreated)
+    } else {
+      workerNodeKey = this.workerChoiceStrategyContext.execute()
+    }
+    return [workerNodeKey, this.workerNodes[workerNodeKey]]
+  }
 
   /**
-   * Send a message to the given worker.
+   * Sends a message to the given worker.
    *
-   * @param worker The worker which should receive the message.
-   * @param message The message.
+   * @param worker - The worker which should receive the message.
+   * @param message - The message.
    */
   protected abstract sendToWorker (
     worker: Worker,
@@ -167,103 +399,204 @@ export abstract class AbstractPool<
   ): void
 
   /**
-   * Adds the given worker to the pool.
+   * Registers a listener callback on the given worker.
    *
-   * @param worker Worker that will be added.
+   * @param worker - The worker which should register a listener.
+   * @param listener - The message listener callback.
    */
-  protected addWorker (worker: Worker): void {
-    const previousWorkerIndex = this.tasks.get(worker)
-    if (previousWorkerIndex !== undefined) {
-      this.tasks.set(worker, previousWorkerIndex + 1)
-    } else {
-      throw Error('Worker could not be found in tasks map')
-    }
-  }
+  protected abstract registerWorkerMessageListener<
+    Message extends Data | Response
+  >(worker: Worker, listener: (message: MessageValue<Message>) => void): void
+
+  /**
+   * Returns a newly created worker.
+   */
+  protected abstract createWorker (): Worker
 
   /**
-   * Removes the given worker from the pool.
+   * Function that can be hooked up when a worker has been newly created and moved to the pool worker nodes.
    *
-   * @param worker Worker that will be removed.
+   * Can be used to update the `maxListeners` or binding the `main-worker`\<-\>`worker` connection if not bind by default.
+   *
+   * @param worker - The newly created worker.
    */
-  protected removeWorker (worker: Worker): void {
-    // Clean worker from data structure
-    const workerIndex = this.workers.indexOf(worker)
-    this.workers.splice(workerIndex, 1)
-    this.tasks.delete(worker)
-  }
+  protected abstract afterWorkerSetup (worker: Worker): void
 
-  public execute (data: Data): Promise<Response> {
-    // Configure worker to handle message with the specified task
-    const worker = this.chooseWorker()
-    this.addWorker(worker)
-    const id = ++this.id
-    const res = this.internalExecute(worker, id)
-    this.sendToWorker(worker, { data: data || ({} as Data), id: id })
-    return res
-  }
+  /**
+   * Creates a new worker and sets it up completely in the pool worker nodes.
+   *
+   * @returns New, completely set up worker.
+   */
+  protected createAndSetupWorker (): Worker {
+    const worker = this.createWorker()
 
-  protected abstract registerWorkerMessageListener (
-    port: Worker,
-    listener: (message: MessageValue<Response>) => void
-  ): void
+    worker.on('message', this.opts.messageHandler ?? EMPTY_FUNCTION)
+    worker.on('error', this.opts.errorHandler ?? EMPTY_FUNCTION)
+    worker.on('online', this.opts.onlineHandler ?? EMPTY_FUNCTION)
+    worker.on('exit', this.opts.exitHandler ?? EMPTY_FUNCTION)
+    worker.once('exit', () => {
+      this.removeWorkerNode(worker)
+    })
 
-  protected abstract unregisterWorkerMessageListener (
-    port: Worker,
-    listener: (message: MessageValue<Response>) => void
-  ): void
+    this.pushWorkerNode(worker)
+
+    this.afterWorkerSetup(worker)
+
+    return worker
+  }
 
-  protected internalExecute (worker: Worker, id: number): Promise<Response> {
-    return new Promise((resolve, reject) => {
-      const listener: (message: MessageValue<Response>) => void = message => {
-        if (message.id === id) {
-          this.unregisterWorkerMessageListener(worker, listener)
-          this.addWorker(worker)
-          if (message.error) reject(message.error)
-          else resolve(message.data as Response)
+  /**
+   * This function is the listener registered for each worker message.
+   *
+   * @returns The listener function to execute when a message is received from a worker.
+   */
+  protected workerListener (): (message: MessageValue<Response>) => void {
+    return message => {
+      if (message.id != null) {
+        // Task execution response received
+        const promiseResponse = this.promiseResponseMap.get(message.id)
+        if (promiseResponse != null) {
+          if (message.error != null) {
+            promiseResponse.reject(message.error)
+          } else {
+            promiseResponse.resolve(message.data as Response)
+          }
+          this.afterTaskExecutionHook(promiseResponse.worker, message)
+          this.promiseResponseMap.delete(message.id)
+          const workerNodeKey = this.getWorkerNodeKey(promiseResponse.worker)
+          if (
+            this.opts.enableTasksQueue === true &&
+            this.tasksQueueSize(workerNodeKey) > 0
+          ) {
+            this.executeTask(
+              workerNodeKey,
+              this.dequeueTask(workerNodeKey) as Task<Data>
+            )
+          }
         }
       }
-      this.registerWorkerMessageListener(worker, listener)
-    })
+    }
+  }
+
+  private checkAndEmitEvents (): void {
+    if (this.opts.enableEvents === true) {
+      if (this.busy) {
+        this.emitter?.emit(PoolEvents.busy)
+      }
+      if (this.type === PoolType.DYNAMIC && this.full) {
+        this.emitter?.emit(PoolEvents.full)
+      }
+    }
   }
 
   /**
-   * Choose a worker for the next task.
+   * Sets the given worker node its tasks usage in the pool.
    *
-   * The default implementation uses a round robin algorithm to distribute the load.
+   * @param workerNode - The worker node.
+   * @param tasksUsage - The worker node tasks usage.
    */
-  protected chooseWorker (): Worker {
-    this.nextWorker =
-      this.nextWorker === this.workers.length - 1 ? 0 : this.nextWorker + 1
-    return this.workers[this.nextWorker]
+  private setWorkerNodeTasksUsage (
+    workerNode: WorkerNode<Worker, Data>,
+    tasksUsage: TasksUsage
+  ): void {
+    workerNode.tasksUsage = tasksUsage
   }
 
   /**
-   * Returns a newly created worker.
+   * Gets the given worker its tasks usage in the pool.
+   *
+   * @param worker - The worker.
+   * @returns The worker tasks usage.
    */
-  protected abstract newWorker (): Worker
+  private getWorkerTasksUsage (worker: Worker): TasksUsage | undefined {
+    const workerNodeKey = this.getWorkerNodeKey(worker)
+    if (workerNodeKey !== -1) {
+      return this.workerNodes[workerNodeKey].tasksUsage
+    }
+    throw new Error('Worker could not be found in the pool worker nodes')
+  }
 
   /**
-   * Function that can be hooked up when a worker has been newly created and moved to the workers registry.
+   * Pushes the given worker in the pool worker nodes.
    *
-   * Can be used to update the `maxListeners` or binding the `main-worker`<->`worker` connection if not bind by default.
+   * @param worker - The worker.
+   * @returns The worker nodes length.
+   */
+  private pushWorkerNode (worker: Worker): number {
+    return this.workerNodes.push({
+      worker,
+      tasksUsage: {
+        run: 0,
+        running: 0,
+        runTime: 0,
+        runTimeHistory: new CircularArray(),
+        avgRunTime: 0,
+        medRunTime: 0,
+        error: 0
+      },
+      tasksQueue: []
+    })
+  }
+
+  /**
+   * Sets the given worker in the pool worker nodes.
    *
-   * @param worker The newly created worker.
+   * @param workerNodeKey - The worker node key.
+   * @param worker - The worker.
+   * @param tasksUsage - The worker tasks usage.
+   * @param tasksQueue - The worker task queue.
    */
-  protected abstract afterNewWorkerPushed (worker: Worker): void
+  private setWorkerNode (
+    workerNodeKey: number,
+    worker: Worker,
+    tasksUsage: TasksUsage,
+    tasksQueue: Array<Task<Data>>
+  ): void {
+    this.workerNodes[workerNodeKey] = {
+      worker,
+      tasksUsage,
+      tasksQueue
+    }
+  }
 
   /**
-   * Creates a new worker for this pool and sets it up completely.
+   * Removes the given worker from the pool worker nodes.
+   *
+   * @param worker - The worker.
    */
-  protected internalNewWorker (): Worker {
-    const worker: Worker = this.newWorker()
-    worker.on('error', this.opts.errorHandler ?? (() => {}))
-    worker.on('online', this.opts.onlineHandler ?? (() => {}))
-    // TODO handle properly when a worker exit
-    worker.on('exit', this.opts.exitHandler ?? (() => {}))
-    this.workers.push(worker)
-    this.afterNewWorkerPushed(worker)
-    // init tasks map
-    this.tasks.set(worker, 0)
-    return worker
+  private removeWorkerNode (worker: Worker): void {
+    const workerNodeKey = this.getWorkerNodeKey(worker)
+    this.workerNodes.splice(workerNodeKey, 1)
+    this.workerChoiceStrategyContext.remove(workerNodeKey)
+  }
+
+  private executeTask (workerNodeKey: number, task: Task<Data>): void {
+    this.beforeTaskExecutionHook(workerNodeKey)
+    this.sendToWorker(this.workerNodes[workerNodeKey].worker, task)
+  }
+
+  private enqueueTask (workerNodeKey: number, task: Task<Data>): number {
+    return this.workerNodes[workerNodeKey].tasksQueue.push(task)
+  }
+
+  private dequeueTask (workerNodeKey: number): Task<Data> | undefined {
+    return this.workerNodes[workerNodeKey].tasksQueue.shift()
+  }
+
+  private tasksQueueSize (workerNodeKey: number): number {
+    return this.workerNodes[workerNodeKey].tasksQueue.length
+  }
+
+  private flushTasksQueue (workerNodeKey: number): void {
+    if (this.tasksQueueSize(workerNodeKey) > 0) {
+      for (const task of this.workerNodes[workerNodeKey].tasksQueue) {
+        this.executeTask(workerNodeKey, task)
+      }
+    }
+  }
+
+  private flushTasksQueueByWorker (worker: Worker): void {
+    const workerNodeKey = this.getWorkerNodeKey(worker)
+    this.flushTasksQueue(workerNodeKey)
   }
 }