gistfile1.js

// This code, run with 10 concurrent users hitting both routes, results in /1 failing with a 404 at a rate ~50% 
var express = require('express');
var app = express.createServer();

app.configure(function(){
  app.use(app.router);
});

function mw(req, res, next) {
  setTimeout(function(){
    next();
  }, 100);
}

app.get('/1', mw, function(req, res){
  res.send(200);
});

app.get('/2', mw, function(req, res){
  res.send(200);
});

app.listen(80);



// As a sanity check, this works
var express = require('express');
var app = express.createServer();

app.configure(function(){
  app.use(app.router);
});

function mw(req, res, next) {
  setTimeout(function(){
    next(req, res);
  }, 100);
}

app.get('/1', function(req, res){
  mw(req, res, function(req, res){
    res.send(200);
  });
});

app.get('/2', function(req, res){
  mw(req, res, function(req, res){
    res.send(200);
  });
});

app.listen(80);