tornadoweb/tornado — pull request #1244 by heewa (2014-11-06 21:10:37+00:00)
Title: Drop callbacks added after ioloop is closed.

Some situations cause a callback to be added to an already closed IOLoop
instance, such as Subprocess, which only adds a callback for handling
when the subprocess exits on a lambda run in a signal handler, which can
be called after the IOLoop exits. (see process.py:273)