fix: only display pool utilization when requirements are met
[poolifier.git] / src / pools / abstract-pool.ts
index b86a3b13a6b538efb4024c0ebe8e49df22e4a1a8..0069fb7fadc61c95196982365adfaf60561069fa 100644 (file)
@@ -4,10 +4,12 @@ import type { MessageValue, PromiseResponseWrapper } from '../utility-types'
 import {
   DEFAULT_WORKER_CHOICE_STRATEGY_OPTIONS,
   EMPTY_FUNCTION,
+  isKillBehavior,
   isPlainObject,
-  median
+  median,
+  round
 } from '../utils'
-import { KillBehaviors, isKillBehavior } from '../worker/worker-options'
+import { KillBehaviors } from '../worker/worker-options'
 import { CircularArray } from '../circular-array'
 import { Queue } from '../queue'
 import {
@@ -19,10 +21,18 @@ import {
   type PoolType,
   PoolTypes,
   type TasksQueueOptions,
-  type WorkerType
+  type WorkerType,
+  WorkerTypes
 } from './pool'
-import type { IWorker, Task, TasksUsage, WorkerNode } from './worker'
+import type {
+  IWorker,
+  MessageHandler,
+  Task,
+  WorkerNode,
+  WorkerUsage
+} from './worker'
 import {
+  Measurements,
   WorkerChoiceStrategies,
   type WorkerChoiceStrategy,
   type WorkerChoiceStrategyOptions
@@ -33,8 +43,8 @@ import { WorkerChoiceStrategyContext } from './selection-strategies/worker-choic
  * 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 execution response. This can only be serializable data.
+ * @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 abstract class AbstractPool<
   Worker extends IWorker,
@@ -62,8 +72,6 @@ export abstract class AbstractPool<
 
   /**
    * Worker choice strategy context referencing a worker choice algorithm implementation.
-   *
-   * Default to a round robin algorithm.
    */
   protected workerChoiceStrategyContext: WorkerChoiceStrategyContext<
   Worker,
@@ -71,6 +79,11 @@ export abstract class AbstractPool<
   Response
   >
 
+  /**
+   * The start timestamp of the pool.
+   */
+  private readonly startTimestamp
+
   /**
    * Constructs a new poolifier pool.
    *
@@ -110,9 +123,11 @@ export abstract class AbstractPool<
 
     this.setupHook()
 
-    for (let i = 1; i <= this.numberOfWorkers; i++) {
+    while (this.workerNodes.length < this.numberOfWorkers) {
       this.createAndSetupWorker()
     }
+
+    this.startTimestamp = performance.now()
   }
 
   private checkFilePath (filePath: string): void {
@@ -195,6 +210,16 @@ export abstract class AbstractPool<
         'Invalid worker choice strategy options: must have a weight for each worker node'
       )
     }
+    if (
+      workerChoiceStrategyOptions.measurement != null &&
+      !Object.values(Measurements).includes(
+        workerChoiceStrategyOptions.measurement
+      )
+    ) {
+      throw new Error(
+        `Invalid worker choice strategy options: invalid measurement '${workerChoiceStrategyOptions.measurement}'`
+      )
+    }
   }
 
   private checkValidTasksQueueOptions (
@@ -203,11 +228,20 @@ export abstract class AbstractPool<
     if (tasksQueueOptions != null && !isPlainObject(tasksQueueOptions)) {
       throw new TypeError('Invalid tasks queue options: must be a plain object')
     }
-    if ((tasksQueueOptions?.concurrency as number) <= 0) {
+    if (
+      tasksQueueOptions?.concurrency != null &&
+      !Number.isSafeInteger(tasksQueueOptions.concurrency)
+    ) {
+      throw new TypeError(
+        'Invalid worker tasks concurrency: must be an integer'
+      )
+    }
+    if (
+      tasksQueueOptions?.concurrency != null &&
+      tasksQueueOptions.concurrency <= 0
+    ) {
       throw new Error(
-        `Invalid worker tasks concurrency '${
-          tasksQueueOptions.concurrency as number
-        }'`
+        `Invalid worker tasks concurrency '${tasksQueueOptions.concurrency}'`
       )
     }
   }
@@ -219,34 +253,80 @@ export abstract class AbstractPool<
       worker: this.worker,
       minSize: this.minSize,
       maxSize: this.maxSize,
+      ...(this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+        .runTime.aggregate &&
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements().runTime
+          .aggregate && { utilization: round(this.utilization) }),
       workerNodes: this.workerNodes.length,
       idleWorkerNodes: this.workerNodes.reduce(
         (accumulator, workerNode) =>
-          workerNode.tasksUsage.running === 0 ? accumulator + 1 : accumulator,
+          workerNode.usage.tasks.executing === 0
+            ? accumulator + 1
+            : accumulator,
         0
       ),
       busyWorkerNodes: this.workerNodes.reduce(
         (accumulator, workerNode) =>
-          workerNode.tasksUsage.running > 0 ? accumulator + 1 : accumulator,
+          workerNode.usage.tasks.executing > 0 ? accumulator + 1 : accumulator,
         0
       ),
-      runningTasks: this.workerNodes.reduce(
+      executedTasks: this.workerNodes.reduce(
         (accumulator, workerNode) =>
-          accumulator + workerNode.tasksUsage.running,
+          accumulator + workerNode.usage.tasks.executed,
+        0
+      ),
+      executingTasks: this.workerNodes.reduce(
+        (accumulator, workerNode) =>
+          accumulator + workerNode.usage.tasks.executing,
         0
       ),
       queuedTasks: this.workerNodes.reduce(
-        (accumulator, workerNode) => accumulator + workerNode.tasksQueue.size,
+        (accumulator, workerNode) =>
+          accumulator + workerNode.usage.tasks.queued,
         0
       ),
       maxQueuedTasks: this.workerNodes.reduce(
         (accumulator, workerNode) =>
-          accumulator + workerNode.tasksQueue.maxSize,
+          accumulator + workerNode.usage.tasks.maxQueued,
+        0
+      ),
+      failedTasks: this.workerNodes.reduce(
+        (accumulator, workerNode) =>
+          accumulator + workerNode.usage.tasks.failed,
         0
       )
     }
   }
 
+  /**
+   * Gets the pool run time.
+   *
+   * @returns The pool run time in milliseconds.
+   */
+  private get runTime (): number {
+    return performance.now() - this.startTimestamp
+  }
+
+  /**
+   * Gets the approximate pool utilization.
+   *
+   * @returns The pool utilization.
+   */
+  private get utilization (): number {
+    const poolRunTimeCapacity = this.runTime * this.maxSize
+    const totalTasksRunTime = this.workerNodes.reduce(
+      (accumulator, workerNode) =>
+        accumulator + workerNode.usage.runTime.aggregate,
+      0
+    )
+    const totalTasksWaitTime = this.workerNodes.reduce(
+      (accumulator, workerNode) =>
+        accumulator + workerNode.usage.waitTime.aggregate,
+      0
+    )
+    return (totalTasksRunTime + totalTasksWaitTime) / poolRunTimeCapacity
+  }
+
   /**
    * Pool type.
    *
@@ -269,11 +349,22 @@ export abstract class AbstractPool<
    */
   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
+  }
+
   /**
    * Gets the given worker its worker node key.
    *
    * @param worker - The worker.
-   * @returns The worker node key if the worker is found in the pool worker nodes, `-1` otherwise.
+   * @returns The worker node key if found in the pool worker nodes, `-1` otherwise.
    */
   private getWorkerNodeKey (worker: Worker): number {
     return this.workerNodes.findIndex(
@@ -294,21 +385,11 @@ export abstract class AbstractPool<
     if (workerChoiceStrategyOptions != null) {
       this.setWorkerChoiceStrategyOptions(workerChoiceStrategyOptions)
     }
-    for (const workerNode of this.workerNodes) {
-      this.setWorkerNodeTasksUsage(workerNode, {
-        ran: 0,
-        running: 0,
-        runTime: 0,
-        runTimeHistory: new CircularArray(),
-        avgRunTime: 0,
-        medRunTime: 0,
-        waitTime: 0,
-        waitTimeHistory: new CircularArray(),
-        avgWaitTime: 0,
-        medWaitTime: 0,
-        error: 0,
-        elu: undefined
-      })
+    for (const [workerNodeKey, workerNode] of this.workerNodes.entries()) {
+      this.setWorkerNodeTasksUsage(
+        workerNode,
+        this.getWorkerUsage(workerNodeKey)
+      )
       this.setWorkerStatistics(workerNode.worker)
     }
   }
@@ -371,10 +452,15 @@ export abstract class AbstractPool<
    */
   protected abstract get busy (): boolean
 
+  /**
+   * Whether worker nodes are executing at least one task.
+   *
+   * @returns Worker nodes busyness boolean status.
+   */
   protected internalBusy (): boolean {
     return (
       this.workerNodes.findIndex(workerNode => {
-        return workerNode.tasksUsage.running === 0
+        return workerNode.usage.tasks.executing === 0
       }) === -1
     )
   }
@@ -400,7 +486,7 @@ export abstract class AbstractPool<
     if (
       this.opts.enableTasksQueue === true &&
       (this.busy ||
-        this.workerNodes[workerNodeKey].tasksUsage.running >=
+        this.workerNodes[workerNodeKey].usage.tasks.executing >=
           ((this.opts.tasksQueueOptions as TasksQueueOptions)
             .concurrency as number))
     ) {
@@ -408,7 +494,6 @@ export abstract class AbstractPool<
     } else {
       this.executeTask(workerNodeKey, submittedTask)
     }
-    this.workerChoiceStrategyContext.update(workerNodeKey)
     this.checkAndEmitEvents()
     // eslint-disable-next-line @typescript-eslint/return-await
     return res
@@ -426,15 +511,15 @@ export abstract class AbstractPool<
   }
 
   /**
-   * Shutdowns the given worker.
+   * Terminates 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
+   * Setup hook to execute code before worker nodes are created in the abstract constructor.
+   * Can be overridden.
    *
    * @virtual
    */
@@ -452,9 +537,15 @@ export abstract class AbstractPool<
    * Can be overridden.
    *
    * @param workerNodeKey - The worker node key.
+   * @param task - The task to execute.
    */
-  protected beforeTaskExecutionHook (workerNodeKey: number): void {
-    ++this.workerNodes[workerNodeKey].tasksUsage.running
+  protected beforeTaskExecutionHook (
+    workerNodeKey: number,
+    task: Task<Data>
+  ): void {
+    const workerUsage = this.workerNodes[workerNodeKey].usage
+    ++workerUsage.tasks.executing
+    this.updateWaitTimeWorkerUsage(workerUsage, task)
   }
 
   /**
@@ -468,78 +559,125 @@ export abstract class AbstractPool<
     worker: Worker,
     message: MessageValue<Response>
   ): void {
-    const workerTasksUsage =
-      this.workerNodes[this.getWorkerNodeKey(worker)].tasksUsage
-    --workerTasksUsage.running
-    ++workerTasksUsage.ran
-    if (message.error != null) {
-      ++workerTasksUsage.error
+    const workerUsage = this.workerNodes[this.getWorkerNodeKey(worker)].usage
+    this.updateTaskStatisticsWorkerUsage(workerUsage, message)
+    this.updateRunTimeWorkerUsage(workerUsage, message)
+    this.updateEluWorkerUsage(workerUsage, message)
+  }
+
+  private updateTaskStatisticsWorkerUsage (
+    workerUsage: WorkerUsage,
+    message: MessageValue<Response>
+  ): void {
+    const workerTaskStatistics = workerUsage.tasks
+    --workerTaskStatistics.executing
+    ++workerTaskStatistics.executed
+    if (message.taskError != null) {
+      ++workerTaskStatistics.failed
     }
-    this.updateRunTimeTasksUsage(workerTasksUsage, message)
-    this.updateWaitTimeTasksUsage(workerTasksUsage, message)
-    this.updateEluTasksUsage(workerTasksUsage, message)
   }
 
-  private updateRunTimeTasksUsage (
-    workerTasksUsage: TasksUsage,
+  private updateRunTimeWorkerUsage (
+    workerUsage: WorkerUsage,
     message: MessageValue<Response>
   ): void {
-    if (this.workerChoiceStrategyContext.getTaskStatistics().runTime) {
-      workerTasksUsage.runTime += message.runTime ?? 0
+    if (
+      this.workerChoiceStrategyContext.getTaskStatisticsRequirements().runTime
+        .aggregate
+    ) {
+      workerUsage.runTime.aggregate += message.taskPerformance?.runTime ?? 0
       if (
-        this.workerChoiceStrategyContext.getTaskStatistics().avgRunTime &&
-        workerTasksUsage.ran !== 0
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements().runTime
+          .average &&
+        workerUsage.tasks.executed !== 0
       ) {
-        workerTasksUsage.avgRunTime =
-          workerTasksUsage.runTime / workerTasksUsage.ran
+        workerUsage.runTime.average =
+          workerUsage.runTime.aggregate /
+          (workerUsage.tasks.executed - workerUsage.tasks.failed)
       }
       if (
-        this.workerChoiceStrategyContext.getTaskStatistics().medRunTime &&
-        message.runTime != null
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements().runTime
+          .median &&
+        message.taskPerformance?.runTime != null
       ) {
-        workerTasksUsage.runTimeHistory.push(message.runTime)
-        workerTasksUsage.medRunTime = median(workerTasksUsage.runTimeHistory)
+        workerUsage.runTime.history.push(message.taskPerformance.runTime)
+        workerUsage.runTime.median = median(workerUsage.runTime.history)
       }
     }
   }
 
-  private updateWaitTimeTasksUsage (
-    workerTasksUsage: TasksUsage,
-    message: MessageValue<Response>
+  private updateWaitTimeWorkerUsage (
+    workerUsage: WorkerUsage,
+    task: Task<Data>
   ): void {
-    if (this.workerChoiceStrategyContext.getTaskStatistics().waitTime) {
-      workerTasksUsage.waitTime += message.waitTime ?? 0
+    const timestamp = performance.now()
+    const taskWaitTime = timestamp - (task.timestamp ?? timestamp)
+    if (
+      this.workerChoiceStrategyContext.getTaskStatisticsRequirements().waitTime
+        .aggregate
+    ) {
+      workerUsage.waitTime.aggregate += taskWaitTime ?? 0
       if (
-        this.workerChoiceStrategyContext.getTaskStatistics().avgWaitTime &&
-        workerTasksUsage.ran !== 0
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+          .waitTime.average &&
+        workerUsage.tasks.executed !== 0
       ) {
-        workerTasksUsage.avgWaitTime =
-          workerTasksUsage.waitTime / workerTasksUsage.ran
+        workerUsage.waitTime.average =
+          workerUsage.waitTime.aggregate /
+          (workerUsage.tasks.executed - workerUsage.tasks.failed)
       }
       if (
-        this.workerChoiceStrategyContext.getTaskStatistics().medWaitTime &&
-        message.waitTime != null
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+          .waitTime.median &&
+        taskWaitTime != null
       ) {
-        workerTasksUsage.waitTimeHistory.push(message.waitTime)
-        workerTasksUsage.medWaitTime = median(workerTasksUsage.waitTimeHistory)
+        workerUsage.waitTime.history.push(taskWaitTime)
+        workerUsage.waitTime.median = median(workerUsage.waitTime.history)
       }
     }
   }
 
-  private updateEluTasksUsage (
-    workerTasksUsage: TasksUsage,
+  private updateEluWorkerUsage (
+    workerUsage: WorkerUsage,
     message: MessageValue<Response>
   ): void {
-    if (this.workerChoiceStrategyContext.getTaskStatistics().elu) {
-      if (workerTasksUsage.elu != null && message.elu != null) {
-        workerTasksUsage.elu = {
-          idle: workerTasksUsage.elu.idle + message.elu.idle,
-          active: workerTasksUsage.elu.active + message.elu.active,
-          utilization:
-            workerTasksUsage.elu.utilization + message.elu.utilization
-        }
-      } else if (message.elu != null) {
-        workerTasksUsage.elu = message.elu
+    if (
+      this.workerChoiceStrategyContext.getTaskStatisticsRequirements().elu
+        .aggregate
+    ) {
+      if (workerUsage.elu != null && message.taskPerformance?.elu != null) {
+        workerUsage.elu.idle.aggregate += message.taskPerformance.elu.idle
+        workerUsage.elu.active.aggregate += message.taskPerformance.elu.active
+        workerUsage.elu.utilization =
+          (workerUsage.elu.utilization +
+            message.taskPerformance.elu.utilization) /
+          2
+      } else if (message.taskPerformance?.elu != null) {
+        workerUsage.elu.idle.aggregate = message.taskPerformance.elu.idle
+        workerUsage.elu.active.aggregate = message.taskPerformance.elu.active
+        workerUsage.elu.utilization = message.taskPerformance.elu.utilization
+      }
+      if (
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements().elu
+          .average &&
+        workerUsage.tasks.executed !== 0
+      ) {
+        const executedTasks =
+          workerUsage.tasks.executed - workerUsage.tasks.failed
+        workerUsage.elu.idle.average =
+          workerUsage.elu.idle.aggregate / executedTasks
+        workerUsage.elu.active.average =
+          workerUsage.elu.active.aggregate / executedTasks
+      }
+      if (
+        this.workerChoiceStrategyContext.getTaskStatisticsRequirements().elu
+          .median &&
+        message.taskPerformance?.elu != null
+      ) {
+        workerUsage.elu.idle.history.push(message.taskPerformance.elu.idle)
+        workerUsage.elu.active.history.push(message.taskPerformance.elu.active)
+        workerUsage.elu.idle.median = median(workerUsage.elu.idle.history)
+        workerUsage.elu.active.median = median(workerUsage.elu.active.history)
       }
     }
   }
@@ -547,32 +685,29 @@ export abstract class AbstractPool<
   /**
    * Chooses a worker node for the next task.
    *
-   * The default worker choice strategy uses a round robin algorithm to distribute the load.
+   * The default worker choice strategy uses a round robin algorithm to distribute the tasks.
    *
    * @returns The worker node key
    */
-  protected chooseWorkerNode (): number {
-    let workerNodeKey: number
-    if (this.type === PoolTypes.dynamic && !this.full && this.internalBusy()) {
-      const workerCreated = this.createAndSetupWorker()
-      this.registerWorkerMessageListener(workerCreated, message => {
-        const currentWorkerNodeKey = this.getWorkerNodeKey(workerCreated)
-        if (
-          isKillBehavior(KillBehaviors.HARD, message.kill) ||
-          (message.kill != null &&
-            this.workerNodes[currentWorkerNodeKey].tasksUsage.running === 0)
-        ) {
-          // Kill message received from the worker: no new tasks are submitted to that worker for a while ( > maxInactiveTime)
-          this.flushTasksQueue(currentWorkerNodeKey)
-          // FIXME: wait for tasks to be finished
-          void (this.destroyWorker(workerCreated) as Promise<void>)
-        }
-      })
-      workerNodeKey = this.getWorkerNodeKey(workerCreated)
-    } else {
-      workerNodeKey = this.workerChoiceStrategyContext.execute()
+  private chooseWorkerNode (): number {
+    if (this.shallCreateDynamicWorker()) {
+      const worker = this.createAndSetupDynamicWorker()
+      if (
+        this.workerChoiceStrategyContext.getStrategyPolicy().useDynamicWorker
+      ) {
+        return this.getWorkerNodeKey(worker)
+      }
     }
-    return workerNodeKey
+    return this.workerChoiceStrategyContext.execute()
+  }
+
+  /**
+   * Conditions for dynamic worker creation.
+   *
+   * @returns Whether to create a dynamic worker or not.
+   */
+  private shallCreateDynamicWorker (): boolean {
+    return this.type === PoolTypes.dynamic && !this.full && this.internalBusy()
   }
 
   /**
@@ -592,23 +727,30 @@ export abstract class AbstractPool<
    * @param worker - The worker which should register a listener.
    * @param listener - The message listener callback.
    */
-  protected abstract registerWorkerMessageListener<
-    Message extends Data | Response
-  >(worker: Worker, listener: (message: MessageValue<Message>) => void): void
+  private registerWorkerMessageListener<Message extends Data | Response>(
+    worker: Worker,
+    listener: (message: MessageValue<Message>) => void
+  ): void {
+    worker.on('message', listener as MessageHandler<Worker>)
+  }
 
   /**
-   * Returns a newly created worker.
+   * Creates a new worker.
+   *
+   * @returns Newly created worker.
    */
   protected abstract createWorker (): Worker
 
   /**
    * Function that can be hooked up when a worker has been newly created and moved to the pool worker nodes.
-   *
-   * Can be used to update the `maxListeners` or binding the `main-worker`\<-\>`worker` connection if not bind by default.
+   * Can be overridden.
    *
    * @param worker - The newly created worker.
    */
-  protected abstract afterWorkerSetup (worker: Worker): void
+  protected afterWorkerSetup (worker: Worker): void {
+    // Listen to worker messages.
+    this.registerWorkerMessageListener(worker, this.workerListener())
+  }
 
   /**
    * Creates a new worker and sets it up completely in the pool worker nodes.
@@ -624,8 +766,6 @@ export abstract class AbstractPool<
       if (this.emitter != null) {
         this.emitter.emit(PoolEvents.error, error)
       }
-    })
-    worker.on('error', () => {
       if (this.opts.restartWorkerOnError === true) {
         this.createAndSetupWorker()
       }
@@ -645,6 +785,31 @@ export abstract class AbstractPool<
     return worker
   }
 
+  /**
+   * Creates a new dynamic worker and sets it up completely in the pool worker nodes.
+   *
+   * @returns New, completely set up dynamic worker.
+   */
+  protected createAndSetupDynamicWorker (): Worker {
+    const worker = this.createAndSetupWorker()
+    this.registerWorkerMessageListener(worker, message => {
+      const workerNodeKey = this.getWorkerNodeKey(worker)
+      if (
+        isKillBehavior(KillBehaviors.HARD, message.kill) ||
+        (message.kill != null &&
+          ((this.opts.enableTasksQueue === false &&
+            this.workerNodes[workerNodeKey].usage.tasks.executing === 0) ||
+            (this.opts.enableTasksQueue === true &&
+              this.workerNodes[workerNodeKey].usage.tasks.executing === 0 &&
+              this.tasksQueueSize(workerNodeKey) === 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>)
+      }
+    })
+    return worker
+  }
+
   /**
    * This function is the listener registered for each worker message.
    *
@@ -652,35 +817,55 @@ export abstract class AbstractPool<
    */
   protected workerListener (): (message: MessageValue<Response>) => void {
     return message => {
-      if (message.id != null) {
+      if (message.workerId != null && message.started != null) {
+        // Worker started message received
+        this.handleWorkerStartedMessage(message)
+      } else 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)
-            if (this.emitter != null) {
-              this.emitter.emit(PoolEvents.taskError, {
-                error: message.error,
-                errorData: message.errorData
-              })
-            }
-          } 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.handleTaskExecutionResponse(message)
+      }
+    }
+  }
+
+  private handleWorkerStartedMessage (message: MessageValue<Response>): void {
+    // Worker started message received
+    const worker = this.getWorkerById(message.workerId as number)
+    if (worker != null) {
+      this.workerNodes[this.getWorkerNodeKey(worker)].info.started =
+        message.started as boolean
+    } else {
+      throw new Error(
+        `Worker started message received from unknown worker '${
+          message.workerId as number
+        }'`
+      )
+    }
+  }
+
+  private handleTaskExecutionResponse (message: MessageValue<Response>): void {
+    const promiseResponse = this.promiseResponseMap.get(message.id as string)
+    if (promiseResponse != null) {
+      if (message.taskError != null) {
+        if (this.emitter != null) {
+          this.emitter.emit(PoolEvents.taskError, message.taskError)
         }
+        promiseResponse.reject(message.taskError.message)
+      } 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)
+      if (
+        this.opts.enableTasksQueue === true &&
+        this.tasksQueueSize(workerNodeKey) > 0
+      ) {
+        this.executeTask(
+          workerNodeKey,
+          this.dequeueTask(workerNodeKey) as Task<Data>
+        )
+      }
+      this.workerChoiceStrategyContext.update(workerNodeKey)
     }
   }
 
@@ -699,13 +884,13 @@ export abstract class AbstractPool<
    * Sets the given worker node its tasks usage in the pool.
    *
    * @param workerNode - The worker node.
-   * @param tasksUsage - The worker node tasks usage.
+   * @param workerUsage - The worker usage.
    */
   private setWorkerNodeTasksUsage (
     workerNode: WorkerNode<Worker, Data>,
-    tasksUsage: TasksUsage
+    workerUsage: WorkerUsage
   ): void {
-    workerNode.tasksUsage = tasksUsage
+    workerNode.usage = workerUsage
   }
 
   /**
@@ -715,47 +900,58 @@ export abstract class AbstractPool<
    * @returns The worker nodes length.
    */
   private pushWorkerNode (worker: Worker): number {
-    return this.workerNodes.push({
+    this.workerNodes.push({
       worker,
-      tasksUsage: {
-        ran: 0,
-        running: 0,
-        runTime: 0,
-        runTimeHistory: new CircularArray(),
-        avgRunTime: 0,
-        medRunTime: 0,
-        waitTime: 0,
-        waitTimeHistory: new CircularArray(),
-        avgWaitTime: 0,
-        medWaitTime: 0,
-        error: 0,
-        elu: undefined
-      },
+      info: { id: this.getWorkerId(worker), started: true },
+      usage: this.getWorkerUsage(),
       tasksQueue: new Queue<Task<Data>>()
     })
+    const workerNodeKey = this.getWorkerNodeKey(worker)
+    this.setWorkerNodeTasksUsage(
+      this.workerNodes[workerNodeKey],
+      this.getWorkerUsage(workerNodeKey)
+    )
+    return this.workerNodes.length
   }
 
   /**
-   * Sets the given worker in the pool worker nodes.
+   * Gets the worker id.
    *
-   * @param workerNodeKey - The worker node key.
    * @param worker - The worker.
-   * @param tasksUsage - The worker tasks usage.
-   * @param tasksQueue - The worker task queue.
+   * @returns The worker id.
    */
-  private setWorkerNode (
-    workerNodeKey: number,
-    worker: Worker,
-    tasksUsage: TasksUsage,
-    tasksQueue: Queue<Task<Data>>
-  ): void {
-    this.workerNodes[workerNodeKey] = {
-      worker,
-      tasksUsage,
-      tasksQueue
+  private getWorkerId (worker: Worker): number | undefined {
+    if (this.worker === WorkerTypes.thread) {
+      return worker.threadId
+    } else if (this.worker === WorkerTypes.cluster) {
+      return worker.id
     }
   }
 
+  // /**
+  //  * Sets the given worker in the pool worker nodes.
+  //  *
+  //  * @param workerNodeKey - The worker node key.
+  //  * @param worker - The worker.
+  //  * @param workerInfo - The worker info.
+  //  * @param workerUsage - The worker usage.
+  //  * @param tasksQueue - The worker task queue.
+  //  */
+  // private setWorkerNode (
+  //   workerNodeKey: number,
+  //   worker: Worker,
+  //   workerInfo: WorkerInfo,
+  //   workerUsage: WorkerUsage,
+  //   tasksQueue: Queue<Task<Data>>
+  // ): void {
+  //   this.workerNodes[workerNodeKey] = {
+  //     worker,
+  //     info: workerInfo,
+  //     usage: workerUsage,
+  //     tasksQueue
+  //   }
+  // }
+
   /**
    * Removes the given worker from the pool worker nodes.
    *
@@ -770,7 +966,7 @@ export abstract class AbstractPool<
   }
 
   private executeTask (workerNodeKey: number, task: Task<Data>): void {
-    this.beforeTaskExecutionHook(workerNodeKey)
+    this.beforeTaskExecutionHook(workerNodeKey, task)
     this.sendToWorker(this.workerNodes[workerNodeKey].worker, task)
   }
 
@@ -786,6 +982,10 @@ export abstract class AbstractPool<
     return this.workerNodes[workerNodeKey].tasksQueue.size
   }
 
+  private tasksMaxQueueSize (workerNodeKey: number): number {
+    return this.workerNodes[workerNodeKey].tasksQueue.maxSize
+  }
+
   private flushTasksQueue (workerNodeKey: number): void {
     if (this.tasksQueueSize(workerNodeKey) > 0) {
       for (let i = 0; i < this.tasksQueueSize(workerNodeKey); i++) {
@@ -795,6 +995,7 @@ export abstract class AbstractPool<
         )
       }
     }
+    this.workerNodes[workerNodeKey].tasksQueue.clear()
   }
 
   private flushTasksQueues (): void {
@@ -806,10 +1007,61 @@ export abstract class AbstractPool<
   private setWorkerStatistics (worker: Worker): void {
     this.sendToWorker(worker, {
       statistics: {
-        runTime: this.workerChoiceStrategyContext.getTaskStatistics().runTime,
-        waitTime: this.workerChoiceStrategyContext.getTaskStatistics().waitTime,
-        elu: this.workerChoiceStrategyContext.getTaskStatistics().elu
+        runTime:
+          this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+            .runTime.aggregate,
+        elu: this.workerChoiceStrategyContext.getTaskStatisticsRequirements()
+          .elu.aggregate
       }
     })
   }
+
+  private getWorkerUsage (workerNodeKey?: number): WorkerUsage {
+    const getTasksQueueSize = (workerNodeKey?: number): number => {
+      return workerNodeKey != null ? this.tasksQueueSize(workerNodeKey) : 0
+    }
+    const getTasksMaxQueueSize = (workerNodeKey?: number): number => {
+      return workerNodeKey != null ? this.tasksMaxQueueSize(workerNodeKey) : 0
+    }
+    return {
+      tasks: {
+        executed: 0,
+        executing: 0,
+        get queued (): number {
+          return getTasksQueueSize(workerNodeKey)
+        },
+        get maxQueued (): number {
+          return getTasksMaxQueueSize(workerNodeKey)
+        },
+        failed: 0
+      },
+      runTime: {
+        aggregate: 0,
+        average: 0,
+        median: 0,
+        history: new CircularArray()
+      },
+      waitTime: {
+        aggregate: 0,
+        average: 0,
+        median: 0,
+        history: new CircularArray()
+      },
+      elu: {
+        idle: {
+          aggregate: 0,
+          average: 0,
+          median: 0,
+          history: new CircularArray()
+        },
+        active: {
+          aggregate: 0,
+          average: 0,
+          median: 0,
+          history: new CircularArray()
+        },
+        utilization: 0
+      }
+    }
+  }
 }