limit_via_async_module.js

// same as previous gist, but now via 'async' library

var async = require('async');

// some dummy rows
var rows = [];
for (var i = 0; i < 10000; i++) {
  rows.push("this is row " + i);
}

var maxRunning = 20;

function callHandler(row, cb) {
  console.log("callHandler for row: " + row);
  setTimeout(function() {
    cb(null);
  }, 500 * Math.random());
}

async.eachLimit(rows, maxRunning, function(row, done) {
  callHandler(row, function(err) {
    if (err) throw new Error(err);
    done();
  });
}, function(err) {
  if (err) throw new Error(err);
  console.log('done');
});