node.js - nodejs async request stop working but no mistake -

var request = require('request'); var async = require('async');  require('http').globalagent.maxsockets = 30; var count = 0;  var urlarr = ['url1','url2'.......] // ten thousand links request  async.eachlimit(urlarr, 30, iterator, function(err) {     console.log('complete'); });  function iterator(url,callback) {     request(url, function(error, response, body) {         console.log(count++);         if (!error && response.statuscode === 200) {             return callback(null);         } else{             return callback(null);         }      }); } 

the code above stop working after few minutes, no error happen, process hoding , not exit, what's problem it?