Queue

Runs submitted tasks with bounded concurrency.

Use Queue when callers should wait their turn and receive the result of their own task.

Import

import { Concurrency, Queue, QueueOptions } from '@haskou/flow';

Signature

class Queue

Constructor

constructor(options = new QueueOptions())

Validation

QueueOptions accepts a positive-integer number or Concurrency. Internally, concurrency is stored as Concurrency.

Throws

This class can throw:

• InvalidQueueConcurrencyError
• QueueClearedError
• any error thrown by an enqueued task

Methods

Method	Description
enqueue(task)	Adds a task to the queue and resolves or rejects with that task result.
run(task)	Alias for enqueue(task) used by FlowPipeline.
clear(error?)	Rejects all pending tasks that have not started. Active tasks continue.
waitUntilIdle()	Resolves when there are no active or pending tasks.
getConcurrency()	Returns configured Concurrency.
getPendingCount()	Returns tasks waiting to start.
getActiveCount()	Returns tasks currently running.

Example

import { Queue, QueueOptions } from '@haskou/flow';

const queue = new Queue(QueueOptions.withConcurrency(4));

const users = await Promise.all([
  queue.enqueue(() => fetchUser('1')),
  queue.enqueue(() => fetchUser('2')),
  queue.enqueue(() => fetchUser('3')),
]);

await queue.waitUntilIdle();

Clearing pending work

import { Queue, QueueClearedError } from '@haskou/flow';

const queue = new Queue();
const pending = queue.enqueue(() => slowWork());

queue.clear();

await pending.catch((error) => {
  if (error instanceof QueueClearedError) {
    // Pending work was cancelled before it started.
  }
});

QueueOptions

Configuration object for Queue.

Signature

class QueueOptions

Constructor

constructor(concurrency: number | Concurrency = Concurrency.DEFAULT)

Factories

Factory	Description
QueueOptions.withConcurrency(concurrency)	Creates options with explicit concurrency.

Methods

Method	Description
getConcurrency()	Returns configured Concurrency.

Notes

• clear() only rejects pending tasks. It does not abort tasks already running.
• waitUntilIdle() is a promise-based completion signal, not an event subscription.
• Use run() when composing with FlowPipeline; use Flow.queue(queue) for fluent composition.

Related

• RateLimiter
• Throttler
• Flow
• Errors