-export interface IPool<Data = unknown, Response = unknown> {
- destroy(): Promise<void>
- execute(data: Data): Promise<Response>
+import { EventEmitter } from 'node:events'
+import { type TransferListItem } from 'node:worker_threads'
+import type { TaskFunction } from '../worker/task-functions'
+import type {
+ ErrorHandler,
+ ExitHandler,
+ IWorker,
+ IWorkerNode,
+ MessageHandler,
+ OnlineHandler,
+ WorkerType
+} from './worker'
+import type {
+ WorkerChoiceStrategy,
+ WorkerChoiceStrategyOptions
+} from './selection-strategies/selection-strategies-types'
+
+/**
+ * Enumeration of pool types.
+ */
+export const PoolTypes = Object.freeze({
+ /**
+ * Fixed pool type.
+ */
+ fixed: 'fixed',
+ /**
+ * Dynamic pool type.
+ */
+ dynamic: 'dynamic'
+} as const)
+
+/**
+ * Pool type.
+ */
+export type PoolType = keyof typeof PoolTypes
+
+/**
+ * Pool events emitter.
+ */
+export class PoolEmitter extends EventEmitter {}
+
+/**
+ * Enumeration of pool events.
+ */
+export const PoolEvents = Object.freeze({
+ ready: 'ready',
+ busy: 'busy',
+ full: 'full',
+ destroy: 'destroy',
+ error: 'error',
+ taskError: 'taskError',
+ backPressure: 'backPressure'
+} as const)
+
+/**
+ * Pool event.
+ */
+export type PoolEvent = keyof typeof PoolEvents
+
+/**
+ * Pool information.
+ */
+export interface PoolInfo {
+ readonly version: string
+ readonly type: PoolType
+ readonly worker: WorkerType
+ readonly started: boolean
+ readonly ready: boolean
+ readonly strategy: WorkerChoiceStrategy
+ readonly minSize: number
+ readonly maxSize: number
+ /** Pool utilization. */
+ readonly utilization?: number
+ /** Pool total worker nodes. */
+ readonly workerNodes: number
+ /** Pool idle worker nodes. */
+ readonly idleWorkerNodes: number
+ /** Pool busy worker nodes. */
+ readonly busyWorkerNodes: number
+ readonly executedTasks: number
+ readonly executingTasks: number
+ readonly queuedTasks?: number
+ readonly maxQueuedTasks?: number
+ readonly backPressure?: boolean
+ readonly stolenTasks?: number
+ readonly failedTasks: number
+ readonly runTime?: {
+ readonly minimum: number
+ readonly maximum: number
+ readonly average?: number
+ readonly median?: number
+ }
+ readonly waitTime?: {
+ readonly minimum: number
+ readonly maximum: number
+ readonly average?: number
+ readonly median?: number
+ }
+}
+
+/**
+ * Worker node tasks queue options.
+ */
+export interface TasksQueueOptions {
+ /**
+ * Maximum tasks queue size per worker node flagging it as back pressured.
+ *
+ * @defaultValue (pool maximum size)^2
+ */
+ readonly size?: number
+ /**
+ * Maximum number of tasks that can be executed concurrently on a worker node.
+ *
+ * @defaultValue 1
+ */
+ readonly concurrency?: number
+ /**
+ * Whether to enable task stealing.
+ *
+ * @defaultValue true
+ */
+ readonly taskStealing?: boolean
+ /**
+ * Whether to enable tasks stealing on back pressure.
+ *
+ * @defaultValue true
+ */
+ readonly tasksStealingOnBackPressure?: boolean
+}
+
+/**
+ * Options for a poolifier pool.
+ *
+ * @typeParam Worker - Type of worker.
+ */
+export interface PoolOptions<Worker extends IWorker> {
+ /**
+ * A function that will listen for online event on each worker.
+ *
+ * @defaultValue `() => {}`
+ */
+ onlineHandler?: OnlineHandler<Worker>
+ /**
+ * A function that will listen for message event on each worker.
+ *
+ * @defaultValue `() => {}`
+ */
+ messageHandler?: MessageHandler<Worker>
+ /**
+ * A function that will listen for error event on each worker.
+ *
+ * @defaultValue `() => {}`
+ */
+ errorHandler?: ErrorHandler<Worker>
+ /**
+ * A function that will listen for exit event on each worker.
+ *
+ * @defaultValue `() => {}`
+ */
+ exitHandler?: ExitHandler<Worker>
+ /**
+ * Whether to start the minimum number of workers at pool initialization.
+ *
+ * @defaultValue true
+ */
+ startWorkers?: boolean
+ /**
+ * The worker choice strategy to use in this pool.
+ *
+ * @defaultValue WorkerChoiceStrategies.ROUND_ROBIN
+ */
+ workerChoiceStrategy?: WorkerChoiceStrategy
+ /**
+ * The worker choice strategy options.
+ */
+ workerChoiceStrategyOptions?: WorkerChoiceStrategyOptions
+ /**
+ * Restart worker on error.
+ */
+ restartWorkerOnError?: boolean
+ /**
+ * Pool events emission.
+ *
+ * @defaultValue true
+ */
+ enableEvents?: boolean
+ /**
+ * Pool worker node tasks queue.
+ *
+ * @defaultValue false
+ */
+ enableTasksQueue?: boolean
+ /**
+ * Pool worker node tasks queue options.
+ */
+ tasksQueueOptions?: TasksQueueOptions
+}
+
+/**
+ * Contract definition for a poolifier pool.
+ *
+ * @typeParam Worker - Type of worker which manages this pool.
+ * @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 interface IPool<
+ Worker extends IWorker,
+ Data = unknown,
+ Response = unknown
+> {
+ /**
+ * Pool information.
+ */
+ readonly info: PoolInfo
+ /**
+ * Pool worker nodes.
+ *
+ * @internal
+ */
+ readonly workerNodes: Array<IWorkerNode<Worker, Data>>
+ /**
+ * Whether the worker node has back pressure (i.e. its tasks queue is full).
+ *
+ * @param workerNodeKey - The worker node key.
+ * @returns `true` if the worker node has back pressure, `false` otherwise.
+ * @internal
+ */
+ readonly hasWorkerNodeBackPressure: (workerNodeKey: number) => boolean
+ /**
+ * Emitter on which events can be listened to.
+ *
+ * Events that can currently be listened to:
+ *
+ * - `'ready'`: Emitted when the number of workers created in the pool has reached the minimum size expected and are ready.
+ * - `'busy'`: Emitted when the number of workers created in the pool has reached the maximum size expected and are executing concurrently their tasks quota.
+ * - `'full'`: Emitted when the pool is dynamic and the number of workers created has reached the maximum size expected.
+ * - `'destroy'`: Emitted when the pool is destroyed.
+ * - `'error'`: Emitted when an uncaught error occurs.
+ * - `'taskError'`: Emitted when an error occurs while executing a task.
+ * - `'backPressure'`: Emitted when all worker nodes have back pressure (i.e. their tasks queue is full: queue size \>= maximum queue size).
+ */
+ readonly emitter?: PoolEmitter
+ /**
+ * Executes the specified function in the worker constructor with the task data input parameter.
+ *
+ * @param data - The optional task input data for the specified task function. This can only be structured-cloneable data.
+ * @param name - The optional name of the task function to execute. If not specified, the default task function will be executed.
+ * @param transferList - An optional array of transferable objects to transfer ownership of. Ownership of the transferred objects is given to the pool's worker_threads worker and they should not be used in the main thread afterwards.
+ * @returns Promise that will be fulfilled when the task is completed.
+ */
+ readonly execute: (
+ data?: Data,
+ name?: string,
+ transferList?: TransferListItem[]
+ ) => Promise<Response>
+ /**
+ * Starts the minimum number of workers in this pool.
+ */
+ readonly start: () => void
+ /**
+ * Terminates all workers in this pool.
+ */
+ readonly destroy: () => Promise<void>
+ /**
+ * Whether the specified task function exists in this pool.
+ *
+ * @param name - The name of the task function.
+ * @returns `true` if the task function exists, `false` otherwise.
+ */
+ readonly hasTaskFunction: (name: string) => boolean
+ /**
+ * Adds a task function to this pool.
+ * If a task function with the same name already exists, it will be overwritten.
+ *
+ * @param name - The name of the task function.
+ * @param taskFunction - The task function.
+ * @returns `true` if the task function was added, `false` otherwise.
+ */
+ readonly addTaskFunction: (
+ name: string,
+ taskFunction: TaskFunction<Data, Response>
+ ) => Promise<boolean>
+ /**
+ * Removes a task function from this pool.
+ *
+ * @param name - The name of the task function.
+ * @returns `true` if the task function was removed, `false` otherwise.
+ */
+ readonly removeTaskFunction: (name: string) => Promise<boolean>
+ /**
+ * Lists the names of task function available in this pool.
+ *
+ * @returns The names of task function available in this pool.
+ */
+ readonly listTaskFunctionNames: () => string[]
+ /**
+ * Sets the default task function in this pool.
+ *
+ * @param name - The name of the task function.
+ * @returns `true` if the default task function was set, `false` otherwise.
+ */
+ readonly setDefaultTaskFunction: (name: string) => Promise<boolean>
+ /**
+ * Sets the worker choice strategy in this pool.
+ *
+ * @param workerChoiceStrategy - The worker choice strategy.
+ * @param workerChoiceStrategyOptions - The worker choice strategy options.
+ */
+ readonly setWorkerChoiceStrategy: (
+ workerChoiceStrategy: WorkerChoiceStrategy,
+ workerChoiceStrategyOptions?: WorkerChoiceStrategyOptions
+ ) => void
+ /**
+ * Sets the worker choice strategy options in this pool.
+ *
+ * @param workerChoiceStrategyOptions - The worker choice strategy options.
+ */
+ readonly setWorkerChoiceStrategyOptions: (
+ workerChoiceStrategyOptions: WorkerChoiceStrategyOptions
+ ) => void
+ /**
+ * Enables/disables the worker node tasks queue in this pool.
+ *
+ * @param enable - Whether to enable or disable the worker node tasks queue.
+ * @param tasksQueueOptions - The worker node tasks queue options.
+ */
+ readonly enableTasksQueue: (
+ enable: boolean,
+ tasksQueueOptions?: TasksQueueOptions
+ ) => void
+ /**
+ * Sets the worker node tasks queue options in this pool.
+ *
+ * @param tasksQueueOptions - The worker node tasks queue options.
+ */
+ readonly setTasksQueueOptions: (tasksQueueOptions: TasksQueueOptions) => void
}