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API

Table of contents

Pool

pool = new FixedThreadPool(numberOfThreads, fileURL, opts)

numberOfThreads (mandatory) Number of workers for this pool.
fileURL (mandatory) URL to a file with a worker implementation.
opts (optional) An object with the pool options properties described below.

pool = new DynamicThreadPool(min, max, fileURL, opts)

min (mandatory) Same as FixedThreadPool numberOfThreads, this number of workers will be always active.
max (mandatory) Max number of workers that this pool can contain, the newly created workers will die after a threshold (default is 1 minute, you can override it in your worker implementation).
fileURL (mandatory) URL to a file with a worker implementation.
opts (optional) An object with the pool options properties described below.

pool.execute(data, name, transferList)

data (optional) An object that you want to pass to your worker task function implementation.
name (optional) A string with the task function name that you want to execute on the worker. Default: 'default'
transferList (optional) An array of transferable objects that you want to transfer to your ThreadWorker implementation.

This method is available on both pool implementations and returns a promise with the task function execution response.

pool.mapExecute(data, name, transferList)

data Iterable objects that you want to pass to your worker task function implementation.
name (optional) A string with the task function name that you want to execute on the worker. Default: 'default'
transferList (optional) An array of transferable objects that you want to transfer to your ThreadWorker) worker implementation.

This method is available on both pool implementations and returns a promise with the task function execution responses array.

pool.start()

This method is available on both pool implementations and will start the minimum number of workers.

pool.destroy()

This method is available on both pool implementations and will call the terminate method on each worker.

pool.hasTaskFunction(name)

name (mandatory) The task function name.

This method is available on both pool implementations and returns a boolean.

pool.addTaskFunction(name, fn)

name (mandatory) The task function name.
fn (mandatory) The task function (data?: Data) => Response | Promise<Response> or task function object { taskFunction: (data?: Data) => Response | Promise<Response>, priority?: number, strategy?: WorkerChoiceStrategy }. Priority range is the same as Unix nice levels.

This method is available on both pool implementations and returns a boolean promise.

pool.removeTaskFunction(name)

name (mandatory) The task function name.

This method is available on both pool implementations and returns a boolean promise.

pool.listTaskFunctionsProperties()

This method is available on both pool implementations and returns an array of the task function properties.

pool.setDefaultTaskFunction(name)

name (mandatory) The task function name.

This method is available on both pool implementations and returns a boolean promise.

Pool options

An object with these properties:

  • messageEventHandler (optional) - A function that will listen for message event on each worker.
    Default: () => {}

  • messageEventErrorHandler (optional) - A function that will listen for message event processing error on each worker.
    Default: () => {}

  • errorEventHandler? (optional) - A function that will listen for error event on each worker.
    Default: () => {}

  • workerChoiceStrategy (optional) - The default worker choice strategy to use in this pool:

    • WorkerChoiceStrategies.ROUND_ROBIN: Submit tasks to worker in a round robin fashion
    • WorkerChoiceStrategies.LEAST_USED: Submit tasks to the worker with the minimum number of executing and queued tasks
    • WorkerChoiceStrategies.LEAST_BUSY: Submit tasks to the worker with the minimum tasks execution time

    WorkerChoiceStrategies.WEIGHTED_ROUND_ROBIN, WorkerChoiceStrategies.INTERLEAVED_WEIGHTED_ROUND_ROBIN and WorkerChoiceStrategies.FAIR_SHARE strategies are targeted to heavy and long tasks.
    Default: WorkerChoiceStrategies.ROUND_ROBIN

  • workerChoiceStrategyOptions (optional) - The worker choice strategy options object to use in this pool.
    Properties:

    • measurement (optional) - The measurement to use in worker choice strategies: runTime, waitTime
    • runTime (optional) - Use the tasks simple moving median runtime instead of the tasks simple moving average runtime in worker choice strategies.
    • waitTime (optional) - Use the tasks simple moving median wait time instead of the tasks simple moving average wait time in worker choice strategies.
    • weights (optional) - The worker weights to use in weighted round robin worker choice strategies: Record<number, number>.

    Default: { runTime: { median: false }, waitTime: { median: false } }

  • startWorkers (optional) - Start the minimum number of workers at pool initialization.
    Default: true

  • restartWorkerOnError (optional) - Restart worker on uncaught error in this pool.
    Default: true

  • enableEvents (optional) - Pool events emission enablement.
    Default: true

  • enableTasksQueue (optional) - Tasks queue per worker enablement in this pool.
    Default: false

  • tasksQueueOptions (optional) - The worker tasks queue options object to use in this pool.
    Properties:

    • size (optional) - The maximum number of tasks that can be queued on a worker before flagging it as back pressured. It must be a positive integer.
    • concurrency (optional) - The maximum number of tasks that can be executed concurrently on a worker. It must be a positive integer.
    • taskStealing (optional) - Task stealing enablement on idle.
    • tasksStealingOnBackPressure (optional) - Tasks stealing enablement under back pressure.
    • tasksStealingRatio (optional) - The ratio of worker nodes that can steal tasks from another worker node. It must be a number between 0 and 1.
    • tasksFinishedTimeout (optional) - Queued tasks finished timeout in milliseconds at worker termination.

    Default: { size: (pool maximum size)^2, concurrency: 1, taskStealing: true, tasksStealingOnBackPressure: true, tasksStealingRatio: 0.6, tasksFinishedTimeout: 2000 }

  • workerOptions (optional) - An object with the worker options to pass to worker. See web worker for more details.
    Default:

    • Deno: { type: 'module' }
    • Bun: { type: 'module', smol: true }
    • Browser: { type: 'module' }

Worker

class YourWorker extends ThreadWorker

taskFunctions (mandatory) The task function or task functions object Record<string, (data?: Data) => Response | Promise<Response> | { taskFunction: (data?: Data) => Response | Promise<Response>, priority?: number, strategy?: WorkerChoiceStrategy }> that you want to execute on the worker. Priority range is the same as Unix nice levels.
opts (optional) An object with these properties:

  • killBehavior (optional) - Dictates if your worker will be deleted in case a task is active on it.
    KillBehaviors.SOFT: If currentTime - lastActiveTime is greater than maxInactiveTime but the worker is stealing tasks or a task is executing or queued, then the worker won't be deleted.
    KillBehaviors.HARD: If currentTime - lastActiveTime is greater than maxInactiveTime but the worker is stealing tasks or a task is executing or queued, then the worker will be deleted.
    This option only apply to the newly created workers.
    Default: KillBehaviors.SOFT

  • maxInactiveTime (optional) - Maximum waiting time in milliseconds for tasks on newly created workers. After this time newly created workers will die. It must be a positive integer greater or equal than 5.
    The last active time of your worker will be updated when it terminates a task.
    If killBehavior is set to KillBehaviors.HARD this value represents also the timeout for the tasks that you submit to the pool, when this timeout expires your tasks is interrupted before completion and removed. The worker is killed if is not part of the minimum size of the pool.
    If killBehavior is set to KillBehaviors.SOFT your tasks have no timeout and your workers will not be terminated until your task is completed.
    Default: 60000

  • killHandler (optional) - A function that will be called when a worker is killed.
    Default: () => {}

YourWorker.hasTaskFunction(name)

name (mandatory) The task function name.

This method is available on both worker implementations and returns { status: boolean, error?: Error }.

YourWorker.addTaskFunction(name, fn)

name (mandatory) The task function name.
fn (mandatory) The task function (data?: Data) => Response | Promise<Response> or task function object { taskFunction: (data?: Data) => Response | Promise<Response>, priority?: number, strategy?: WorkerChoiceStrategy }. Priority range is the same as Unix nice levels.

This method is available on both worker implementations and returns { status: boolean, error?: Error }.

YourWorker.removeTaskFunction(name)

name (mandatory) The task function name.

This method is available on both worker implementations and returns { status: boolean, error?: Error }.

YourWorker.listTaskFunctionsProperties()

This method is available on both worker implementations and returns an array of the task function properties.

YourWorker.setDefaultTaskFunction(name)

name (mandatory) The task function name.

This method is available on both worker implementations and returns { status: boolean, error?: Error }.