Basically, it spawns threads for each 'dreamer.' Then they spawn more threads for each dream level, and wait for the lucid_dreamer-s in lower levels to accomplish their task, while printing what's going on. Think of it like the good old dining philosopher's program, where threads represent the diners.

Here's a slightly more lucid explanation: http://calacanis.joshontheweb.com/wp-content/uploads/2010/07...