Concurrency Limit

Limit the concurrency of certain operations. Uses promises.

Usage

var concurrencyLimit = require('concurrencylimit');

// returns a function that limits to <= 3 concurrent tasks
var limit = concurrencyLimit(3);

var resultPromises = [1, 2, 3, 4, 5].map(function (n) {

  // limit will make there are at most only 3
  // outstanding tasks at any given moment
  return limit(function() {

    return new Promise(function (result, error) {
      console.log('task started');
      setTimeout(function () {
        console.log('task finished');
        result(n + 1);
      }, 1000);
    });
  });
});

Promise.all(resultPromises).then(function (results) {
  console.log(results);
});

API

var concurrencyLimit = require('concurrencylimit');

var limit = concurrencyLimit(n);

n, the maximum number of oustanding tasks allowed by limit

limit(function);

Given function returns a promise, makes sure that at most only n functions have been called, but have not returned yet. As soon as one of the function calls have returned the next is executed.