Resource Pool

An easy to use resource pool, including support for recycling resources, with excellent TypeScript typings.

Installation

npm install --save ts-resource-pool

Usage

A simplified example of writing a connection pooling mail client:

const net = require('net')
const ResourcePool = require('ts-resource-pool')

const factory = {
  async create () {
    const connection = net.createConnection(25, 'aspmx.l.google.com')
    connection.write('HELO LinusU.local\r\n')
    return connection
  },
  async recycle (connection, error) {
    // Create a new connection if an error happened
    if (error) {
      await this.destroy(connection)
      return this.create()
    }

    // Otherwise, just issue a `RSET` command and reuse the connection
    connection.write('RSET\r\n')
    return connection
  },
  async destory (connection) {
    connection.write('QUIT\r\n')
    connection.end()
  }
}

const pool = new ResourcePool(factory, 5)

for (let i = 0; i < 25; i++) {
  pool.use(async (connection) => {
    connection.write('MAIL FROM: <linus@LinusU.local>\r\n')
    connection.write('RCPT TO: <spam@gmail.com>\r\n')
  })
}

The ResourcePool will make sure that there is never more than 5 connections open at the same time, and it will also reuse the connections instead of closing and opening new sockets.

API

new ResourcePool(factory: Factory, concurrency: number = 1)

Create a new ResourcePool with the specificed factory and concurrency limit.

The factory must at the very least provide a create function, which returns a fresh resource. This can optionally be an async function.

It can also optionally provide:

• A destroy function, that takes a used resource and an optional error that occured, and tears it down.
• A recycle function, that takes a used resource and an optional error that occured, and returns a resource (possibly the same) that's ready for use again.

ResourcePool#use (fn: (resource: T) => R | PromiseLike<R>): Promise<R>

Aquire a resource, then execute (possibly async) function fn, and finally returns the resource to the pool. Returns a Promise of whatever the function fn returns.

The resource will be returned even if fn throws or returns a rejected Promise. In this case, the Promise returned will also be rejected with that error.