ext-channel-queue

channel-queue

A queue management library with channels.

About

This library provides a queue system, organised by channels (or "topics"), that allows for finer-grain control over asynchronous method execution. It allows for queuing tasks by channels (string-based names) - tasks executing sequentially when the previous task is done. It also allows for 3 priority levels : normal, high and tail.

Check out the API documentation.

Installation

Simply run:

npm install @buttercup/channel-queue --save

Usage

The simplest usage is to just queue some tasks:

const ChannelQueue = require("@buttercup/channel-queue");

const queue = new ChannelQueue();
const work = queue.channel("myChannel").enqueue(() => 123);
// 'work' will resolve with 123

const someChannel = queue.channel("someChannel");
someChannel.enqueue(job1);
someChannel.enqueue(job2);
someChannel.enqueue(job3);

You can push tasks above others by setting them as high-priority:

const ChannelQueue = require("@buttercup/channel-queue");
const { TASK_TYPE_HIGH_PRIORITY } = ChannelQueue.Task;

const queue = new ChannelQueue();
const workChannel = queue.channel("work");
// some other tasks added to the queue...
workChannel.enqueue(importantJobMethod, TASK_TYPE_HIGH_PRIORITY).then(result => {
    // 'result' is the resolved result from the 'importantJobMethod' function
});

Tasks can also be run as "low" priority or at the tail end of the queue:

const ChannelQueue = require("@buttercup/channel-queue");
const { TASK_TYPE_TAIL } = ChannelQueue.Task;

const queue = new ChannelQueue();
const workChannel = queue.channel("work");
// some other tasks added to the queue...
workChannel.enqueue(runNearEnd, TASK_TYPE_TAIL);

Stacking

Items can be "stacked", meaning that if specified, items can be limited to only 1 pending item in queue. All items of the same stack name would simply queue on the same item and not create more tasks. The stack can be specified when enqueuing:

const ChannelQueue = require("@buttercup/channel-queue");

const queue = new ChannelQueue();
const workChannel = queue.channel("work");

const promise1 = workChannel.enqueue(saveWorkFn, undefined, /* Stack ID */ "save");
// work start
const promise2 = workChannel.enqueue(saveWorkFn, undefined, "save");
const promise3 = workChannel.enqueue(saveWorkFn, undefined, "save");
// promise2 and promise3 will be equal, as promise2 was still in the queue when promise3

Parallel Execution

Tasks can be run in parallel using the ParallelChannel class. You can create a parallel channel, in place of a regular channel, by calling ChannelQueue#createParallelChannel:

const ChannelQueue = require("@buttercup/channel-queue");

const queue = new ChannelQueue();
const workChannel = queue.createParallelChannel("work");
workChannel.enqueue(someTask);

// The same channel can be fetched later using the familiar channel() method:
queue.channel("work"); // The parallel channel

Parallel channels, like their name implies, can run tasks in parallel. Instead of running them head-to-tail like regular channels, parallel channels can execute many tasks side-by-side. You can also limit them to a certain number of threads (default is 2) by calling queue.createParallelChannel("name", 5) (where 5 is the maximum number of simultaneous tasks).

Parallel channels by default do not run tasks of different priorities simultaneously. This means that if the current running tasks are high-priority, no normal priority tasks will be started. This feature can be disabled by running parallelChannel.canRunAcrossTaskTypes = true.

Clearing

You can clear all enqueued items in a Channel by calling clear():

queue.channel("myChannel").clear();

Development & Supported Node Versions

This library is intended to be used with NodeJS version 6 and later.

To contribute, clone this project and run npm install before beginning development.

To test, simply run npm test.