Using node-chimera on a server

I wrote a test script using node-chimera (similar to phantomjs). It has a server interface that has some processing that relies on the output of node-chimera. The test will just return "DONE" if everything works fine. And right now everything works fine. However, when I tried this with multiple concurrent users, the code seems to be loading forever and never returned anything. What did I do wrong?

The code: https://gist.github.com/zybler/5244301