Here, and a bit below, a Map's (a synchronized WeakHashMap) size is checked as being >= 0 to twiddle the state of the polling field.

I'm pretty sure WeakHashMap would never return a size < 0. I haven't fully grasped the rest of the file (should this only be set iff there's more than 1 active thread?), but certainly if (map.size() >= 0) is always going to be true.