refactor: refine worker termination error message
[poolifier.git] / src / pools / abstract-pool.ts
index 10a2d514246748a7d21187f22b6b8400b1697864..f76ad2f55bf4326383077456d7414aa8c023ea2e 100644 (file)
@@ -1,6 +1,7 @@
 import { randomUUID } from 'node:crypto'
 import { performance } from 'node:perf_hooks'
 import { existsSync } from 'node:fs'
+import { type TransferListItem } from 'node:worker_threads'
 import type {
   MessageValue,
   PromiseResponseWrapper,
@@ -30,7 +31,6 @@ import {
 import type {
   IWorker,
   IWorkerNode,
-  MessageHandler,
   WorkerInfo,
   WorkerType,
   WorkerUsage
@@ -65,17 +65,15 @@ export abstract class AbstractPool<
   public readonly emitter?: PoolEmitter
 
   /**
-   * The execution response promise map.
+   * The task 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.
    */
-  protected promiseResponseMap: Map<
-  string,
-  PromiseResponseWrapper<Worker, Response>
-  > = new Map<string, PromiseResponseWrapper<Worker, Response>>()
+  protected promiseResponseMap: Map<string, PromiseResponseWrapper<Response>> =
+    new Map<string, PromiseResponseWrapper<Response>>()
 
   /**
    * Worker choice strategy context referencing a worker choice algorithm implementation.
@@ -108,7 +106,9 @@ export abstract class AbstractPool<
     protected readonly opts: PoolOptions<Worker>
   ) {
     if (!this.isMain()) {
-      throw new Error('Cannot start a pool from a worker!')
+      throw new Error(
+        'Cannot start a pool from a worker with the same type as the pool'
+      )
     }
     this.checkNumberOfWorkers(this.numberOfWorkers)
     this.checkFilePath(this.filePath)
@@ -117,6 +117,7 @@ export abstract class AbstractPool<
     this.chooseWorkerNode = this.chooseWorkerNode.bind(this)
     this.executeTask = this.executeTask.bind(this)
     this.enqueueTask = this.enqueueTask.bind(this)
+    this.dequeueTask = this.dequeueTask.bind(this)
     this.checkAndEmitEvents = this.checkAndEmitEvents.bind(this)
 
     if (this.opts.enableEvents === true) {
@@ -174,13 +175,21 @@ export abstract class AbstractPool<
 
   protected checkDynamicPoolSize (min: number, max: number): void {
     if (this.type === PoolTypes.dynamic) {
-      if (min > max) {
+      if (max == null) {
+        throw new Error(
+          'Cannot instantiate a dynamic pool without specifying the maximum pool size'
+        )
+      } else if (!Number.isSafeInteger(max)) {
+        throw new TypeError(
+          'Cannot instantiate a dynamic pool with a non safe integer maximum pool size'
+        )
+      } else if (min > max) {
         throw new RangeError(
           'Cannot instantiate a dynamic pool with a maximum pool size inferior to the minimum pool size'
         )
       } else if (max === 0) {
         throw new RangeError(
-          'Cannot instantiate a dynamic pool with a pool size equal to zero'
+          'Cannot instantiate a dynamic pool with a maximum pool size equal to zero'
         )
       } else if (min === max) {
         throw new RangeError(
@@ -287,7 +296,7 @@ export abstract class AbstractPool<
         0
       ) < this.numberOfWorkers
     ) {
-      this.createAndSetupWorker()
+      this.createAndSetupWorkerNode()
     }
   }
 
@@ -328,16 +337,20 @@ export abstract class AbstractPool<
           accumulator + workerNode.usage.tasks.executing,
         0
       ),
-      queuedTasks: this.workerNodes.reduce(
-        (accumulator, workerNode) =>
-          accumulator + workerNode.usage.tasks.queued,
-        0
-      ),
-      maxQueuedTasks: this.workerNodes.reduce(
-        (accumulator, workerNode) =>
-          accumulator + (workerNode.usage.tasks?.maxQueued ?? 0),
-        0
-      ),
+      ...(this.opts.enableTasksQueue === true && {
+        queuedTasks: this.workerNodes.reduce(
+          (accumulator, workerNode) =>
+            accumulator + workerNode.usage.tasks.queued,
+          0
+        )
+      }),
+      ...(this.opts.enableTasksQueue === true && {
+        maxQueuedTasks: this.workerNodes.reduce(
+          (accumulator, workerNode) =>
+            accumulator + (workerNode.usage.tasks?.maxQueued ?? 0),
+          0
+        )
+      }),
       failedTasks: this.workerNodes.reduce(
         (accumulator, workerNode) =>
           accumulator + workerNode.usage.tasks.failed,
@@ -349,14 +362,14 @@ export abstract class AbstractPool<
           minimum: round(
             Math.min(
               ...this.workerNodes.map(
-                workerNode => workerNode.usage.runTime?.minimum ?? Infinity
+                (workerNode) => workerNode.usage.runTime?.minimum ?? Infinity
               )
             )
           ),
           maximum: round(
             Math.max(
               ...this.workerNodes.map(
-                workerNode => workerNode.usage.runTime?.maximum ?? -Infinity
+                (workerNode) => workerNode.usage.runTime?.maximum ?? -Infinity
               )
             )
           ),
@@ -377,7 +390,7 @@ export abstract class AbstractPool<
             median: round(
               median(
                 this.workerNodes.map(
-                  workerNode => workerNode.usage.runTime?.median ?? 0
+                  (workerNode) => workerNode.usage.runTime?.median ?? 0
                 )
               )
             )
@@ -390,14 +403,14 @@ export abstract class AbstractPool<
           minimum: round(
             Math.min(
               ...this.workerNodes.map(
-                workerNode => workerNode.usage.waitTime?.minimum ?? Infinity
+                (workerNode) => workerNode.usage.waitTime?.minimum ?? Infinity
               )
             )
           ),
           maximum: round(
             Math.max(
               ...this.workerNodes.map(
-                workerNode => workerNode.usage.waitTime?.maximum ?? -Infinity
+                (workerNode) => workerNode.usage.waitTime?.maximum ?? -Infinity
               )
             )
           ),
@@ -418,7 +431,7 @@ export abstract class AbstractPool<
             median: round(
               median(
                 this.workerNodes.map(
-                  workerNode => workerNode.usage.waitTime?.median ?? 0
+                  (workerNode) => workerNode.usage.waitTime?.median ?? 0
                 )
               )
             )
@@ -428,6 +441,9 @@ export abstract class AbstractPool<
     }
   }
 
+  /**
+   * The pool readiness boolean status.
+   */
   private get ready (): boolean {
     return (
       this.workerNodes.reduce(
@@ -441,7 +457,7 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Gets the approximate pool utilization.
+   * The approximate pool utilization.
    *
    * @returns The pool utilization.
    */
@@ -462,38 +478,27 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Pool type.
+   * The pool type.
    *
    * If it is `'dynamic'`, it provides the `max` property.
    */
   protected abstract get type (): PoolType
 
   /**
-   * Gets the worker type.
+   * The worker type.
    */
   protected abstract get worker (): WorkerType
 
   /**
-   * Pool minimum size.
+   * The pool minimum size.
    */
   protected abstract get minSize (): number
 
   /**
-   * Pool maximum size.
+   * The pool maximum size.
    */
   protected abstract get maxSize (): number
 
-  /**
-   * Get the worker given its id.
-   *
-   * @param workerId - The worker id.
-   * @returns The worker if found in the pool worker nodes, `undefined` otherwise.
-   */
-  private getWorkerById (workerId: number): Worker | undefined {
-    return this.workerNodes.find(workerNode => workerNode.info.id === workerId)
-      ?.worker
-  }
-
   /**
    * Checks if the worker id sent in the received message from a worker is valid.
    *
@@ -503,7 +508,7 @@ export abstract class AbstractPool<
   private checkMessageWorkerId (message: MessageValue<Response>): void {
     if (
       message.workerId != null &&
-      this.getWorkerById(message.workerId) == null
+      this.getWorkerNodeKeyByWorkerId(message.workerId) === -1
     ) {
       throw new Error(
         `Worker message received from unknown worker '${message.workerId}'`
@@ -517,9 +522,21 @@ export abstract class AbstractPool<
    * @param worker - The worker.
    * @returns The worker node key if found in the pool worker nodes, `-1` otherwise.
    */
-  private getWorkerNodeKey (worker: Worker): number {
+  private getWorkerNodeKeyByWorker (worker: Worker): number {
+    return this.workerNodes.findIndex(
+      (workerNode) => workerNode.worker === worker
+    )
+  }
+
+  /**
+   * Gets the worker node key given its worker id.
+   *
+   * @param workerId - The worker id.
+   * @returns The worker node key if the worker id is found in the pool worker nodes, `-1` otherwise.
+   */
+  private getWorkerNodeKeyByWorkerId (workerId: number): number {
     return this.workerNodes.findIndex(
-      workerNode => workerNode.worker === worker
+      (workerNode) => workerNode.info.id === workerId
     )
   }
 
@@ -536,9 +553,9 @@ export abstract class AbstractPool<
     if (workerChoiceStrategyOptions != null) {
       this.setWorkerChoiceStrategyOptions(workerChoiceStrategyOptions)
     }
-    for (const workerNode of this.workerNodes) {
+    for (const [workerNodeKey, workerNode] of this.workerNodes.entries()) {
       workerNode.resetUsage()
-      this.setWorkerStatistics(workerNode.worker)
+      this.sendWorkerStatisticsMessageToWorker(workerNodeKey)
     }
   }
 
@@ -601,76 +618,105 @@ export abstract class AbstractPool<
   protected abstract get busy (): boolean
 
   /**
-   * Whether worker nodes are executing at least one task.
+   * Whether worker nodes are executing concurrently their tasks quota or not.
    *
    * @returns Worker nodes busyness boolean status.
    */
   protected internalBusy (): boolean {
-    return (
-      this.workerNodes.findIndex(workerNode => {
-        return workerNode.usage.tasks.executing === 0
-      }) === -1
-    )
+    if (this.opts.enableTasksQueue === true) {
+      return (
+        this.workerNodes.findIndex(
+          (workerNode) =>
+            workerNode.info.ready &&
+            workerNode.usage.tasks.executing <
+              (this.opts.tasksQueueOptions?.concurrency as number)
+        ) === -1
+      )
+    } else {
+      return (
+        this.workerNodes.findIndex(
+          (workerNode) =>
+            workerNode.info.ready && workerNode.usage.tasks.executing === 0
+        ) === -1
+      )
+    }
   }
 
   /** @inheritDoc */
-  public async execute (data?: Data, name?: string): Promise<Response> {
-    const timestamp = performance.now()
-    const workerNodeKey = this.chooseWorkerNode()
-    const submittedTask: Task<Data> = {
-      name: name ?? DEFAULT_TASK_NAME,
-      // eslint-disable-next-line @typescript-eslint/consistent-type-assertions
-      data: data ?? ({} as Data),
-      timestamp,
-      workerId: this.getWorkerInfo(workerNodeKey).id as number,
-      id: randomUUID()
-    }
-    const res = new Promise<Response>((resolve, reject) => {
-      this.promiseResponseMap.set(submittedTask.id as string, {
+  public async execute (
+    data?: Data,
+    name?: string,
+    transferList?: TransferListItem[]
+  ): Promise<Response> {
+    return await new Promise<Response>((resolve, reject) => {
+      if (name != null && typeof name !== 'string') {
+        reject(new TypeError('name argument must be a string'))
+      }
+      if (transferList != null && !Array.isArray(transferList)) {
+        reject(new TypeError('transferList argument must be an array'))
+      }
+      const timestamp = performance.now()
+      const workerNodeKey = this.chooseWorkerNode()
+      const task: Task<Data> = {
+        name: name ?? DEFAULT_TASK_NAME,
+        // eslint-disable-next-line @typescript-eslint/consistent-type-assertions
+        data: data ?? ({} as Data),
+        transferList,
+        timestamp,
+        workerId: this.getWorkerInfo(workerNodeKey).id as number,
+        taskId: randomUUID()
+      }
+      this.promiseResponseMap.set(task.taskId as string, {
         resolve,
         reject,
-        worker: this.workerNodes[workerNodeKey].worker
+        workerNodeKey
       })
+      if (
+        this.opts.enableTasksQueue === false ||
+        (this.opts.enableTasksQueue === true &&
+          this.workerNodes[workerNodeKey].usage.tasks.executing <
+            (this.opts.tasksQueueOptions?.concurrency as number))
+      ) {
+        this.executeTask(workerNodeKey, task)
+      } else {
+        this.enqueueTask(workerNodeKey, task)
+      }
+      this.checkAndEmitEvents()
     })
-    if (
-      this.opts.enableTasksQueue === true &&
-      (this.busy ||
-        this.workerNodes[workerNodeKey].usage.tasks.executing >=
-          ((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
   }
 
   /** @inheritDoc */
   public async destroy (): Promise<void> {
     await Promise.all(
-      this.workerNodes.map(async (workerNode, workerNodeKey) => {
-        this.flushTasksQueue(workerNodeKey)
-        // FIXME: wait for tasks to be finished
-        const workerExitPromise = new Promise<void>(resolve => {
-          workerNode.worker.on('exit', () => {
-            resolve()
-          })
-        })
-        await this.destroyWorker(workerNode.worker)
-        await workerExitPromise
+      this.workerNodes.map(async (_, workerNodeKey) => {
+        await this.destroyWorkerNode(workerNodeKey)
       })
     )
   }
 
+  protected async sendKillMessageToWorker (
+    workerNodeKey: number,
+    workerId: number
+  ): Promise<void> {
+    const waitForKillResponse = new Promise<void>((resolve, reject) => {
+      this.registerWorkerMessageListener(workerNodeKey, (message) => {
+        if (message.kill === 'success') {
+          resolve()
+        } else if (message.kill === 'failure') {
+          reject(new Error(`Worker ${workerId} kill message handling failed`))
+        }
+      })
+    })
+    this.sendToWorker(workerNodeKey, { kill: true, workerId })
+    await waitForKillResponse
+  }
+
   /**
-   * Terminates the given worker.
+   * Terminates the worker node given its worker node key.
    *
-   * @param worker - A worker within `workerNodes`.
+   * @param workerNodeKey - The worker node key.
    */
-  protected abstract destroyWorker (worker: Worker): void | Promise<void>
+  protected abstract destroyWorkerNode (workerNodeKey: number): Promise<void>
 
   /**
    * Setup hook to execute code before worker nodes are created in the abstract constructor.
@@ -712,14 +758,13 @@ export abstract class AbstractPool<
    * Hook executed after the worker task execution.
    * Can be overridden.
    *
-   * @param worker - The worker.
+   * @param workerNodeKey - The worker node key.
    * @param message - The received message.
    */
   protected afterTaskExecutionHook (
-    worker: Worker,
+    workerNodeKey: number,
     message: MessageValue<Response>
   ): void {
-    const workerNodeKey = this.getWorkerNodeKey(worker)
     const workerUsage = this.workerNodes[workerNodeKey].usage
     this.updateTaskStatisticsWorkerUsage(workerUsage, message)
     this.updateRunTimeWorkerUsage(workerUsage, message)
@@ -808,15 +853,15 @@ export abstract class AbstractPool<
    *
    * The default worker choice strategy uses a round robin algorithm to distribute the tasks.
    *
-   * @returns The worker node key
+   * @returns The chosen worker node key
    */
   private chooseWorkerNode (): number {
     if (this.shallCreateDynamicWorker()) {
-      const worker = this.createAndSetupDynamicWorker()
+      const workerNodeKey = this.createAndSetupDynamicWorkerNode()
       if (
         this.workerChoiceStrategyContext.getStrategyPolicy().useDynamicWorker
       ) {
-        return this.getWorkerNodeKey(worker)
+        return workerNodeKey
       }
     }
     return this.workerChoiceStrategyContext.execute()
@@ -832,14 +877,16 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Sends a message to the given worker.
+   * Sends a message to worker given its worker node key.
    *
-   * @param worker - The worker which should receive the message.
+   * @param workerNodeKey - The worker node key.
    * @param message - The message.
+   * @param transferList - The optional array of transferable objects.
    */
   protected abstract sendToWorker (
-    worker: Worker,
-    message: MessageValue<Data>
+    workerNodeKey: number,
+    message: MessageValue<Data>,
+    transferList?: TransferListItem[]
   ): void
 
   /**
@@ -850,25 +897,26 @@ export abstract class AbstractPool<
   protected abstract createWorker (): Worker
 
   /**
-   * Creates a new worker and sets it up completely in the pool worker nodes.
+   * Creates a new, completely set up worker node.
    *
-   * @returns New, completely set up worker.
+   * @returns New, completely set up worker node key.
    */
-  protected createAndSetupWorker (): Worker {
+  protected createAndSetupWorkerNode (): number {
     const worker = this.createWorker()
 
     worker.on('message', this.opts.messageHandler ?? EMPTY_FUNCTION)
     worker.on('error', this.opts.errorHandler ?? EMPTY_FUNCTION)
-    worker.on('error', error => {
-      const workerNodeKey = this.getWorkerNodeKey(worker)
+    worker.on('error', (error) => {
+      const workerNodeKey = this.getWorkerNodeKeyByWorker(worker)
       const workerInfo = this.getWorkerInfo(workerNodeKey)
       workerInfo.ready = false
+      this.workerNodes[workerNodeKey].closeChannel()
       this.emitter?.emit(PoolEvents.error, error)
       if (this.opts.restartWorkerOnError === true && !this.starting) {
         if (workerInfo.dynamic) {
-          this.createAndSetupDynamicWorker()
+          this.createAndSetupDynamicWorkerNode()
         } else {
-          this.createAndSetupWorker()
+          this.createAndSetupWorkerNode()
         }
       }
       if (this.opts.enableTasksQueue === true) {
@@ -881,79 +929,100 @@ export abstract class AbstractPool<
       this.removeWorkerNode(worker)
     })
 
-    this.addWorkerNode(worker)
+    const workerNodeKey = this.addWorkerNode(worker)
 
-    this.afterWorkerSetup(worker)
+    this.afterWorkerNodeSetup(workerNodeKey)
 
-    return worker
+    return workerNodeKey
   }
 
   /**
-   * Creates a new dynamic worker and sets it up completely in the pool worker nodes.
+   * Creates a new, completely set up dynamic worker node.
    *
-   * @returns New, completely set up dynamic worker.
+   * @returns New, completely set up dynamic worker node key.
    */
-  protected createAndSetupDynamicWorker (): Worker {
-    const worker = this.createAndSetupWorker()
-    this.registerWorkerMessageListener(worker, message => {
-      const workerNodeKey = this.getWorkerNodeKey(worker)
+  protected createAndSetupDynamicWorkerNode (): number {
+    const workerNodeKey = this.createAndSetupWorkerNode()
+    this.registerWorkerMessageListener(workerNodeKey, (message) => {
+      const localWorkerNodeKey = this.getWorkerNodeKeyByWorkerId(
+        message.workerId
+      )
+      const workerUsage = this.workerNodes[localWorkerNodeKey].usage
+      // Kill message received from worker
       if (
         isKillBehavior(KillBehaviors.HARD, message.kill) ||
-        (message.kill != null &&
+        (isKillBehavior(KillBehaviors.SOFT, message.kill) &&
           ((this.opts.enableTasksQueue === false &&
-            this.workerNodes[workerNodeKey].usage.tasks.executing === 0) ||
+            workerUsage.tasks.executing === 0) ||
             (this.opts.enableTasksQueue === true &&
-              this.workerNodes[workerNodeKey].usage.tasks.executing === 0 &&
-              this.tasksQueueSize(workerNodeKey) === 0)))
+              workerUsage.tasks.executing === 0 &&
+              this.tasksQueueSize(localWorkerNodeKey) === 0)))
       ) {
-        // Kill message received from the worker: no new tasks are submitted to that worker for a while ( > maxInactiveTime)
-        void (this.destroyWorker(worker) as Promise<void>)
+        this.destroyWorkerNode(localWorkerNodeKey).catch(EMPTY_FUNCTION)
       }
     })
-    const workerInfo = this.getWorkerInfoByWorker(worker)
+    const workerInfo = this.getWorkerInfo(workerNodeKey)
+    this.sendToWorker(workerNodeKey, {
+      checkActive: true,
+      workerId: workerInfo.id as number
+    })
     workerInfo.dynamic = true
     if (this.workerChoiceStrategyContext.getStrategyPolicy().useDynamicWorker) {
       workerInfo.ready = true
     }
-    this.sendToWorker(worker, {
-      checkActive: true,
-      workerId: workerInfo.id as number
-    })
-    return worker
+    return workerNodeKey
   }
 
   /**
-   * Registers a listener callback on the given worker.
+   * Registers a listener callback on the worker given its worker node key.
    *
-   * @param worker - The worker which should register a listener.
+   * @param workerNodeKey - The worker node key.
    * @param listener - The message listener callback.
    */
-  private registerWorkerMessageListener<Message extends Data | Response>(
-    worker: Worker,
+  protected abstract registerWorkerMessageListener<
+    Message extends Data | Response
+  >(
+    workerNodeKey: number,
     listener: (message: MessageValue<Message>) => void
-  ): void {
-    worker.on('message', listener as MessageHandler<Worker>)
-  }
+  ): void
 
   /**
-   * Function that can be hooked up when a worker has been newly created and moved to the pool worker nodes.
+   * Method hooked up after a worker node has been newly created.
    * Can be overridden.
    *
-   * @param worker - The newly created worker.
+   * @param workerNodeKey - The newly created worker node key.
    */
-  protected afterWorkerSetup (worker: Worker): void {
+  protected afterWorkerNodeSetup (workerNodeKey: number): void {
     // Listen to worker messages.
-    this.registerWorkerMessageListener(worker, this.workerListener())
-    // Send startup message to worker.
-    this.sendWorkerStartupMessage(worker)
-    // Setup worker task statistics computation.
-    this.setWorkerStatistics(worker)
+    this.registerWorkerMessageListener(workerNodeKey, this.workerListener())
+    // Send the startup message to worker.
+    this.sendStartupMessageToWorker(workerNodeKey)
+    // Send the worker statistics message to worker.
+    this.sendWorkerStatisticsMessageToWorker(workerNodeKey)
   }
 
-  private sendWorkerStartupMessage (worker: Worker): void {
-    this.sendToWorker(worker, {
-      ready: false,
-      workerId: this.getWorkerInfoByWorker(worker).id as number
+  /**
+   * Sends the startup message to worker given its worker node key.
+   *
+   * @param workerNodeKey - The worker node key.
+   */
+  protected abstract sendStartupMessageToWorker (workerNodeKey: number): void
+
+  /**
+   * Sends the worker statistics message to worker given its worker node key.
+   *
+   * @param workerNodeKey - The worker node key.
+   */
+  private sendWorkerStatisticsMessageToWorker (workerNodeKey: number): void {
+    this.sendToWorker(workerNodeKey, {
+      statistics: {
+        runTime:
+          this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+            .runTime.aggregate,
+        elu: this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+          .elu.aggregate
+      },
+      workerId: this.getWorkerInfo(workerNodeKey).id as number
     })
   }
 
@@ -961,6 +1030,7 @@ export abstract class AbstractPool<
     while (this.tasksQueueSize(workerNodeKey) > 0) {
       let targetWorkerNodeKey: number = workerNodeKey
       let minQueuedTasks = Infinity
+      let executeTask = false
       for (const [workerNodeId, workerNode] of this.workerNodes.entries()) {
         const workerInfo = this.getWorkerInfo(workerNodeId)
         if (
@@ -968,6 +1038,12 @@ export abstract class AbstractPool<
           workerInfo.ready &&
           workerNode.usage.tasks.queued === 0
         ) {
+          if (
+            this.workerNodes[workerNodeId].usage.tasks.executing <
+            (this.opts.tasksQueueOptions?.concurrency as number)
+          ) {
+            executeTask = true
+          }
           targetWorkerNodeKey = workerNodeId
           break
         }
@@ -980,34 +1056,41 @@ export abstract class AbstractPool<
           targetWorkerNodeKey = workerNodeId
         }
       }
-      this.enqueueTask(
-        targetWorkerNodeKey,
-        this.dequeueTask(workerNodeKey) as Task<Data>
-      )
+      if (executeTask) {
+        this.executeTask(
+          targetWorkerNodeKey,
+          this.dequeueTask(workerNodeKey) as Task<Data>
+        )
+      } else {
+        this.enqueueTask(
+          targetWorkerNodeKey,
+          this.dequeueTask(workerNodeKey) as Task<Data>
+        )
+      }
     }
   }
 
   /**
-   * This function is the listener registered for each worker message.
+   * This method 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 => {
+    return (message) => {
       this.checkMessageWorkerId(message)
       if (message.ready != null) {
-        // Worker ready response received
+        // Worker ready response received from worker
         this.handleWorkerReadyResponse(message)
-      } else if (message.id != null) {
-        // Task execution response received
+      } else if (message.taskId != null) {
+        // Task execution response received from worker
         this.handleTaskExecutionResponse(message)
       }
     }
   }
 
   private handleWorkerReadyResponse (message: MessageValue<Response>): void {
-    this.getWorkerInfoByWorker(
-      this.getWorkerById(message.workerId) as Worker
+    this.getWorkerInfo(
+      this.getWorkerNodeKeyByWorkerId(message.workerId)
     ).ready = message.ready as boolean
     if (this.emitter != null && this.ready) {
       this.emitter.emit(PoolEvents.ready, this.info)
@@ -1015,7 +1098,9 @@ export abstract class AbstractPool<
   }
 
   private handleTaskExecutionResponse (message: MessageValue<Response>): void {
-    const promiseResponse = this.promiseResponseMap.get(message.id as string)
+    const promiseResponse = this.promiseResponseMap.get(
+      message.taskId as string
+    )
     if (promiseResponse != null) {
       if (message.taskError != null) {
         this.emitter?.emit(PoolEvents.taskError, message.taskError)
@@ -1023,12 +1108,14 @@ export abstract class AbstractPool<
       } else {
         promiseResponse.resolve(message.data as Response)
       }
-      this.afterTaskExecutionHook(promiseResponse.worker, message)
-      this.promiseResponseMap.delete(message.id as string)
-      const workerNodeKey = this.getWorkerNodeKey(promiseResponse.worker)
+      const workerNodeKey = promiseResponse.workerNodeKey
+      this.afterTaskExecutionHook(workerNodeKey, message)
+      this.promiseResponseMap.delete(message.taskId as string)
       if (
         this.opts.enableTasksQueue === true &&
-        this.tasksQueueSize(workerNodeKey) > 0
+        this.tasksQueueSize(workerNodeKey) > 0 &&
+        this.workerNodes[workerNodeKey].usage.tasks.executing <
+          (this.opts.tasksQueueOptions?.concurrency as number)
       ) {
         this.executeTask(
           workerNodeKey,
@@ -1051,28 +1138,21 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Gets the worker information from the given worker node key.
+   * Gets the worker information given its worker node key.
    *
    * @param workerNodeKey - The worker node key.
+   * @returns The worker information.
    */
-  private getWorkerInfo (workerNodeKey: number): WorkerInfo {
+  protected getWorkerInfo (workerNodeKey: number): WorkerInfo {
     return this.workerNodes[workerNodeKey].info
   }
 
-  /**
-   * Gets the worker information from the given worker.
-   *
-   * @param worker - The worker.
-   */
-  private getWorkerInfoByWorker (worker: Worker): WorkerInfo {
-    return this.workerNodes[this.getWorkerNodeKey(worker)].info
-  }
-
   /**
    * Adds the given worker in the pool worker nodes.
    *
    * @param worker - The worker.
-   * @returns The worker nodes length.
+   * @returns The added worker node key.
+   * @throws {@link https://nodejs.org/api/errors.html#class-error} If the added worker node is not found.
    */
   private addWorkerNode (worker: Worker): number {
     const workerNode = new WorkerNode<Worker, Data>(worker, this.worker)
@@ -1080,7 +1160,12 @@ export abstract class AbstractPool<
     if (this.starting) {
       workerNode.info.ready = true
     }
-    return this.workerNodes.push(workerNode)
+    this.workerNodes.push(workerNode)
+    const workerNodeKey = this.getWorkerNodeKeyByWorker(worker)
+    if (workerNodeKey === -1) {
+      throw new Error('Worker node not found')
+    }
+    return workerNodeKey
   }
 
   /**
@@ -1089,7 +1174,7 @@ export abstract class AbstractPool<
    * @param worker - The worker.
    */
   private removeWorkerNode (worker: Worker): void {
-    const workerNodeKey = this.getWorkerNodeKey(worker)
+    const workerNodeKey = this.getWorkerNodeKeyByWorker(worker)
     if (workerNodeKey !== -1) {
       this.workerNodes.splice(workerNodeKey, 1)
       this.workerChoiceStrategyContext.remove(workerNodeKey)
@@ -1097,14 +1182,14 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Executes the given task on the given worker.
+   * Executes the given task on the worker given its worker node key.
    *
-   * @param worker - The worker.
+   * @param workerNodeKey - The worker node key.
    * @param task - The task to execute.
    */
   private executeTask (workerNodeKey: number, task: Task<Data>): void {
     this.beforeTaskExecutionHook(workerNodeKey, task)
-    this.sendToWorker(this.workerNodes[workerNodeKey].worker, task)
+    this.sendToWorker(workerNodeKey, task, task.transferList)
   }
 
   private enqueueTask (workerNodeKey: number, task: Task<Data>): number {
@@ -1119,7 +1204,7 @@ export abstract class AbstractPool<
     return this.workerNodes[workerNodeKey].tasksQueueSize()
   }
 
-  private flushTasksQueue (workerNodeKey: number): void {
+  protected flushTasksQueue (workerNodeKey: number): void {
     while (this.tasksQueueSize(workerNodeKey) > 0) {
       this.executeTask(
         workerNodeKey,
@@ -1134,17 +1219,4 @@ export abstract class AbstractPool<
       this.flushTasksQueue(workerNodeKey)
     }
   }
-
-  private setWorkerStatistics (worker: Worker): void {
-    this.sendToWorker(worker, {
-      statistics: {
-        runTime:
-          this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
-            .runTime.aggregate,
-        elu: this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
-          .elu.aggregate
-      },
-      workerId: this.getWorkerInfoByWorker(worker).id as number
-    })
-  }
 }