def add_callback(self, callback, *args, **kwargs):
if thread.get_ident() != self._thread_ident:
# If we're not on the IOLoop's thread, we need to synchronize
# with other threads, or waking logic will induce a race.
with self._callback_lock:
if self._closing:
return
list_empty = not self._callbacks
self._callbacks.append(functools.partial(
stack_context.wrap(callback), *args, **kwargs))
if list_empty:
# If we're not in the IOLoop's thread, and we added the
# first callback to an empty list, we may need to wake it
# up (it may wake up on its own, but an occasional extra
# wake is harmless). Waking up a polling IOLoop is
# relatively expensive, so we try to avoid it when we can.
self._waker.wake()
else:
if self._closing:
return
# If we're on the IOLoop's thread, we don't need the lock,
# since we don't need to wake anyone, just add the
# callback. Blindly insert into self._callbacks. This is
# safe even from signal handlers because the GIL makes
# list.append atomic. One subtlety is that if the signal
# is interrupting another thread holding the
# _callback_lock block in IOLoop.start, we may modify
# either the old or new version of self._callbacks, but
# either way will work.
self._callbacks.append(functools.partial(
stack_context.wrap(callback), *args, **kwargs))
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