throat

Throttle the parallelism of an asynchronous (promise returning) function / functions

throat

Throttle the parallelism of an asynchronous, promise returning, function / functions. This has special utility when you set the concurrency to 1. That way you get a mutually exclusive lock.

Installation

npm install throat

API

throat(concurrency)

This returns a function that acts a bit like a lock (exactly as a lock if concurrency is 1).

Example, only 2 of the following functions will execute at any one time:

// with polyfill or in iojs 
require('promise/polyfill')
var throat = require('throat')(2)
// alternatively provide your own promise implementation 
var throat = require('throat')(require('promise'))(2)
 
var resA = throat(function () {
  //async stuff 
  return promise
})
var resA = throat(function () {
  //async stuff 
  return promise
})
var resA = throat(function () {
  //async stuff 
  return promise
})
var resA = throat(function () {
  //async stuff 
  return promise
})
var resA = throat(function () {
  //async stuff 
  return promise
})

throat(concurrency, worker)

This returns a function that is an exact copy of worker except that it will only execute up to concurrency times in parallel before further requests are queued:

// with polyfill or in iojs 
require('promise/polyfill')
var throat = require('throat')
// alternatively provide your own promise implementation 
var throat = require('throat')(require('promise'))
 
var input = ['fileA.txt', 'fileB.txt', 'fileC.txt', 'fileD.txt']
var data = Promise.all(input.map(throat(2, function (fileName) {
  return readFile(fileName)
})))

Only 2 files will be read at a time, sometimes limiting parallelism in this way can improve scalability.

License

MIT