throttle-queue

A promise based priority queue with task deduplication, concurrency control, serial resolution and aging.

Installation

    npm install throttle-queue
            # OR
    yarn add throttle-queue

Features

• Async jobs with promise support
• Job Deduplication
• Priority Assignment
• Concurrency control
• Aging of jobs to prevent starvation

All while keeping your code execution serial :)

Usage

const Queue = require("throttle-queue");
const taskQueue = new Queue({ concurrency: 2 });

taskQueue.setExecutor(async ({ pokemon }) => {
  const url = `https://pokeapi.co/api/v2/pokemon/${pokemon}`;
  const response = await fetch(url);
  return await response.json();
});

const result = await taskQueue.process({ pokemon: "mew" }, "mew")
console.log('I found', result)

API

Creating a queue

const queue = new Queue(options);

options

| option | type | default value | description | | ----------- | ---------------- | ------------- | ----------------------------------------------------------------------------------------------------- | | concurrency | number | 1 | Maximum number of jobs that can be run concurrently at the same time | | aging | boolean | true | Whether to age older jobs in order to prevent starvation | | maxAge | number (seconds) | Infinity | Time in seconds after which the job will expire and removed from the queue if not executed till then. |

Setting a task executor (required)

const queue = new Queue(options);

queue.setExecutor(params => {
  console.log("received params", params);
  return "done";
});

The task executor picks up the highest priority task from the queue and executes it. It can be synchrounous or asynchronous. When sync, it is internally wrapped in a promise.

Adding a task to the queue

const queue = new Queue(options)
queue.setExecutor((params) => {
  console.log('received params', params)
  return 'done'
})

const result = await queue.process(params, id, options)

arguments

• params - Object - An data object to pass to the task executor
• id - The id of the task. This is used for deduplication.
• options -

| option | type | default value | description | | -------- | ---------------- | ------------------------ | --------------------------------------------------------------------------------------- | | priority | number | 'Queue.priority.LOW' (5) | Priority of the job. | | maxAge | number (seconds) | Infinity | Time in seconds after which the job will expire. If not set, the global maxAge is used. |

### Clearing the queue
```js
const queue = new Queue()
queue.clear()

Clears the queues of all waiting jobs. Jobs in execution are not disturbed.

Todo

• Optimize perf for cases when there huge number of jobs in the ready queue.