With Tornado's gen module, you can turn Python generators into
full-featured coroutines, but coordination among these coroutines is
difficult without mutexes, semaphores, and queues.

Toro provides to Tornado coroutines a set of locking primitives and
queues analogous to those that Gevent provides to Greenlets, or that
the standard library provides to threads.

(Note that these primitives and queues are not actually thread-safe and
cannot be used in place of those from the standard library -- they are
meant to coordinate Tornado coroutines in single-threaded apps, not to
protect shared objects in multithreaded apps.)