These are green threads, according to the article. That means that they must work cooperatively (they're not system threads). That means that if any of the th

These are green threads, according to the article. That means that they must work cooperatively (they're not system threads). That means that if any of the threads blocks - say on reading a secondary web service - then all threads will block. That's because the thread switching is managed by the VM, not the kernel, so it has no control over kernel level blocking calls. I know nothing about Ruby, so perhaps I am misunderstanding, but this would explain what he is seeing and is consistent with what he describes.