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How to run a coroutine and wait it result from a sync func when the loop is running?

I have a code like the foolowing:
def render():
loop = asyncio.get_event_loop()
async def test():
await asyncio.sleep(2)
print("hi")
return 200
if loop.is_running():
result = asyncio.ensure_future(test())
else:
result = loop.run_until_complete(test())
When the loop is not running is quite easy, just use loop.run_until_complete and it return the coro result but if the loop is already running (my blocking code running in app which is already running the loop) I cannot use loop.run_until_complete since it will raise an exception; when I call asyncio.ensure_future the task gets scheduled and run, but I want to wait there for the result, does anybody knows how to do this? Docs are not very clear how to do this.
I tried passing a concurrent.futures.Future calling set_result inside the coro and then calling Future.result() on my blocking code, but it doesn't work, it blocks there and do not let anything else to run. ANy help would be appreciated.

To implement runner with the proposed design, you would need a way to single-step the event loop from a callback running inside it. Asyncio explicitly forbids recursive event loops, so this approach is a dead end.
Given that constraint, you have two options:
make render() itself a coroutine;
execute render() (and its callers) in a thread different than the thread that runs the asyncio event loop.
Assuming #1 is out of the question, you can implement the #2 variant of render() like this:
def render():
loop = _event_loop # can't call get_event_loop()
async def test():
await asyncio.sleep(2)
print("hi")
return 200
future = asyncio.run_coroutine_threadsafe(test(), loop)
result = future.result()
Note that you cannot use asyncio.get_event_loop() in render because the event loop is not (and should not be) set for that thread. Instead, the code that spawns the runner thread must call asyncio.get_event_loop() and send it to the thread, or just leave it in a global variable or a shared structure.

Waiting Synchronously for an Asynchronous Coroutine
If an asyncio event loop is already running by calling loop.run_forever, it will block the executing thread until loop.stop is called [see the docs]. Therefore, the only way for a synchronous wait is to run the event loop on a dedicated thread, schedule the asynchronous function on the loop and wait for it synchronously from another thread.
For this I have composed my own minimal solution following the answer by user4815162342. I have also added the parts for cleaning up the loop when all work is finished [see loop.close].
The main function in the code below runs the event loop on a dedicated thread, schedules several tasks on the event loop, plus the task the result of which is to be awaited synchronously. The synchronous wait will block until the desired result is ready. Finally, the loop is closed and cleaned up gracefully along with its thread.
The dedicated thread and the functions stop_loop, run_forever_safe, and await_sync can be encapsulated in a module or a class.
For thread-safery considerations, see section “Concurrency and Multithreading” in asyncio docs.
import asyncio
import threading
#----------------------------------------
def stop_loop(loop):
''' stops an event loop '''
loop.stop()
print (".: LOOP STOPPED:", loop.is_running())
def run_forever_safe(loop):
''' run a loop for ever and clean up after being stopped '''
loop.run_forever()
# NOTE: loop.run_forever returns after calling loop.stop
#-- cancell all tasks and close the loop gracefully
print(".: CLOSING LOOP...")
# source: <https://xinhuang.github.io/posts/2017-07-31-common-mistakes-using-python3-asyncio.html>
loop_tasks_all = asyncio.Task.all_tasks(loop=loop)
for task in loop_tasks_all: task.cancel()
# NOTE: `cancel` does not guarantee that the Task will be cancelled
for task in loop_tasks_all:
if not (task.done() or task.cancelled()):
try:
# wait for task cancellations
loop.run_until_complete(task)
except asyncio.CancelledError: pass
#END for
print(".: ALL TASKS CANCELLED.")
loop.close()
print(".: LOOP CLOSED:", loop.is_closed())
def await_sync(task):
''' synchronously waits for a task '''
while not task.done(): pass
print(".: AWAITED TASK DONE")
return task.result()
#----------------------------------------
async def asyncTask(loop, k):
''' asynchronous task '''
print("--start async task %s" % k)
await asyncio.sleep(3, loop=loop)
print("--end async task %s." % k)
key = "KEY#%s" % k
return key
def main():
loop = asyncio.new_event_loop() # construct a new event loop
#-- closures for running and stopping the event-loop
run_loop_forever = lambda: run_forever_safe(loop)
close_loop_safe = lambda: loop.call_soon_threadsafe(stop_loop, loop)
#-- make dedicated thread for running the event loop
thread = threading.Thread(target=run_loop_forever)
#-- add some tasks along with my particular task
myTask = asyncio.run_coroutine_threadsafe(asyncTask(loop, 100200300), loop=loop)
otherTasks = [asyncio.run_coroutine_threadsafe(asyncTask(loop, i), loop=loop)
for i in range(1, 10)]
#-- begin the thread to run the event-loop
print(".: EVENT-LOOP THREAD START")
thread.start()
#-- _synchronously_ wait for the result of my task
result = await_sync(myTask) # blocks until task is done
print("* final result of my task:", result)
#... do lots of work ...
print("*** ALL WORK DONE ***")
#========================================
# close the loop gracefully when everything is finished
close_loop_safe()
thread.join()
#----------------------------------------
main()

here is my case, my whole programe is async, but call some sync lib, then callback to my async func.
follow the answer by user4815162342.
import asyncio
async def asyncTask(k):
''' asynchronous task '''
print("--start async task %s" % k)
# await asyncio.sleep(3, loop=loop)
await asyncio.sleep(3)
print("--end async task %s." % k)
key = "KEY#%s" % k
return key
def my_callback():
print("here i want to call my async func!")
future = asyncio.run_coroutine_threadsafe(asyncTask(1), LOOP)
return future.result()
def sync_third_lib(cb):
print("here will call back to your code...")
cb()
async def main():
print("main start...")
print("call sync third lib ...")
await asyncio.to_thread(sync_third_lib, my_callback)
# await loop.run_in_executor(None, func=sync_third_lib)
print("another work...keep async...")
await asyncio.sleep(2)
print("done!")
LOOP = asyncio.get_event_loop()
LOOP.run_until_complete(main())

Schedule task to running event loop from synchronous code

Consider this program, where the mainloop and the coroutine to stop it are actually implemented by a library I'm using.
import asyncio
import signal
running = True
async def stop():
global running
print("setting false")
running = False
await asyncio.sleep(3)
print("reached end")
async def mainloop():
while running:
print("loop")
await asyncio.sleep(1)
def handle_signal():
loop.create_task(stop())
loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGINT, handle_signal)
loop.run_until_complete(mainloop())
loop.close()
I need to call the stop coroutine to stop the mainloop when the program recieves a signal. Although when scheduling the stop coroutine using asyncio.BaseEventLoop.create_task it first stops the mainloop which stops the event loop and the stop coroutine can't finish:
$ ./test.py
loop
loop
loop
^Csetting false
Task was destroyed but it is pending!
task: <Task pending coro=<stop() done, defined at ./test.py:7> wait_for=<Future pending cb=[Task._wakeup()]>>
How to add the coroutine to the running event loop while making the event loop wait until it is complete?

As you discovered, the problem is that the event loop is only waiting for mainloop() to complete, leaving stop() pending, which asyncio correctly complains about.
If handle_signal and the top-level code are under your control, you can easily replace looping until mainloop completes with looping until a custom coroutine completes. This coroutine would invoke mainloop and then wait for the cleanup code to finish:
# ... omitted definition of mainloop() and stop()
# list of tasks that must be waited for before we can actually exit
_cleanup = []
async def run():
await mainloop()
# wait for all _cleanup tasks to finish
await asyncio.wait(_cleanup)
def handle_signal():
# schedule stop() to run, and also add it to the list of
# tasks run() must wait for before it is done
_cleanup.append(loop.create_task(stop()))
loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGINT, handle_signal)
loop.run_until_complete(run())
loop.close()
Another option, which doesn't require the new run() coroutine (but still requires the modified handle_signal), is to issue a second run_until_complete() after mainloop completes:
# handle_signal and _cleanup defined as above
loop = asyncio.get_event_loop()
loop.add_signal_handler(signal.SIGINT, handle_signal)
loop.run_until_complete(mainloop())
if _cleanup:
loop.run_until_complete(asyncio.wait(_cleanup))
loop.close()

Exit program while tasks in default executor are still running

I have a program which executes some long-running, synchronous tasks and may need to exit even when some of those tasks haven't finished yet. The following is a simple program which start such a task in main(). main() immediately returns after that and thus the program should exit.
import asyncio, time
def synchronous_task():
for i in range(5):
print(i)
time.sleep(1)
async def main():
loop.run_in_executor(None, synchronous_task)
loop = asyncio.get_event_loop()
loop.run_until_complete(main())
print('Main thread exiting.')
But instead I get this when running the script:
$ python3.5 test3.py
0
Main thread exiting.
1
2
3
4
What is the intended way to handle such a situation? The event loop's default executor already uses daemon threads and terminating the program without cleanup would be OK in my case, but I don't want to use os._exit().

Your question more about how to kill a thread. Look for this post for details.
Solution with event would be:
import asyncio, time
from functools import partial
import threading
import concurrent
def synchronous_task(ev):
for i in range(5):
if ev.isSet():
print('terminating thread')
return
print(i)
time.sleep(1)
async def main():
ev = threading.Event() # see: https://stackoverflow.com/a/325528/1113207
loop.run_in_executor(None, partial(synchronous_task, ev))
await asyncio.sleep(2) # give thread some time to execute, to see results
ev.set()
loop = asyncio.get_event_loop()
executor = concurrent.futures.ThreadPoolExecutor(5)
loop.set_default_executor(executor)
try:
loop.run_until_complete(main())
finally:
loop.run_until_complete(loop.shutdown_asyncgens())
executor.shutdown(wait=True) # see: https://stackoverflow.com/a/32615276/1113207
loop.close()
print('Main thread exiting.')
Result:
0
1
terminating thread
Main thread exiting.
[Finished in 2.2s]

Please explain "Task was destroyed but it is pending!" after cancelling tasks

I am learning asyncio with Python 3.4.2 and I use it to continuously listen on an IPC bus, while gbulb listens on the DBus.
I created a function listen_to_ipc_channel_layer that continuously listens for incoming messages on the IPC channel and passes the message to message_handler.
I am also listening to SIGTERM and SIGINT. When I send a SIGTERM to the python process running the code you find at the bottom, the script should terminate gracefully.
The problem I am having is the following warning:
got signal 15: exit
Task was destroyed but it is pending!
task: <Task pending coro=<listen_to_ipc_channel_layer() running at /opt/mainloop-test.py:23> wait_for=<Future cancelled>>
Process finished with exit code 0
…with the following code:
import asyncio
import gbulb
import signal
import asgi_ipc as asgi
def main():
asyncio.async(listen_to_ipc_channel_layer())
loop = asyncio.get_event_loop()
for sig in (signal.SIGINT, signal.SIGTERM):
loop.add_signal_handler(sig, ask_exit)
# Start listening on the Linux IPC bus for incoming messages
loop.run_forever()
loop.close()
#asyncio.coroutine
def listen_to_ipc_channel_layer():
"""Listens to the Linux IPC bus for messages"""
while True:
message_handler(message=channel_layer.receive(["my_channel"]))
try:
yield from asyncio.sleep(0.1)
except asyncio.CancelledError:
break
def ask_exit():
loop = asyncio.get_event_loop()
for task in asyncio.Task.all_tasks():
task.cancel()
loop.stop()
if __name__ == "__main__":
gbulb.install()
# Connect to the IPC bus
channel_layer = asgi.IPCChannelLayer(prefix="my_channel")
main()
I still only understand very little of asyncio, but I think I know what is going on. While waiting for yield from asyncio.sleep(0.1) the signal handler caught the SIGTERM and in that process it calls task.cancel().
Shouldn't this trigger the CancelledError within the while True: loop? (Because it is not, but that is how I understand "Calling cancel() will throw a CancelledError to the wrapped coroutine").
Eventually loop.stop() is called which stops the loop without waiting for either yield from asyncio.sleep(0.1) to return a result or even the whole coroutine listen_to_ipc_channel_layer.
Please correct me if I am wrong.
I think the only thing I need to do is to make my program wait for the yield from asyncio.sleep(0.1) to return a result and/or coroutine to break out the while loop and finish.
I believe I confuse a lot of things. Please help me get those things straight so that I can figure out how to gracefully close the event loop without warning.

The problem comes from closing the loop immediately after cancelling the tasks. As the cancel() docs state
"This arranges for a CancelledError to be thrown into the wrapped coroutine on the next cycle through the event loop."
Take this snippet of code:
import asyncio
import signal
async def pending_doom():
await asyncio.sleep(2)
print(">> Cancelling tasks now")
for task in asyncio.Task.all_tasks():
task.cancel()
print(">> Done cancelling tasks")
asyncio.get_event_loop().stop()
def ask_exit():
for task in asyncio.Task.all_tasks():
task.cancel()
async def looping_coro():
print("Executing coroutine")
while True:
try:
await asyncio.sleep(0.25)
except asyncio.CancelledError:
print("Got CancelledError")
break
print("Done waiting")
print("Done executing coroutine")
asyncio.get_event_loop().stop()
def main():
asyncio.async(pending_doom())
asyncio.async(looping_coro())
loop = asyncio.get_event_loop()
for sig in (signal.SIGINT, signal.SIGTERM):
loop.add_signal_handler(sig, ask_exit)
loop.run_forever()
# I had to manually remove the handlers to
# avoid an exception on BaseEventLoop.__del__
for sig in (signal.SIGINT, signal.SIGTERM):
loop.remove_signal_handler(sig)
if __name__ == '__main__':
main()
Notice ask_exit cancels the tasks but does not stop the loop, on the next cycle looping_coro() stops it. The output if you cancel it is:
Executing coroutine
Done waiting
Done waiting
Done waiting
Done waiting
^CGot CancelledError
Done executing coroutine
Notice how pending_doom cancels and stops the loop immediately after. If you let it run until the pending_doom coroutines awakes from the sleep you can see the same warning you're getting:
Executing coroutine
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
Done waiting
>> Cancelling tasks now
>> Done cancelling tasks
Task was destroyed but it is pending!
task: <Task pending coro=<looping_coro() running at canceling_coroutines.py:24> wait_for=<Future cancelled>>

The meaning of the issue is that a loop doesn't have time to finish all the tasks.
This arranges for a CancelledError to be thrown into the wrapped coroutine on the next cycle through the event loop.
There is no chance to do a "next cycle" of the loop in your approach. To make it properly you should move a stop operation to a separate non-cyclic coroutine to give your loop a chance to finish.
Second significant thing is CancelledError raising.
Unlike Future.cancel(), this does not guarantee that the task will be cancelled: the exception might be caught and acted upon, delaying cancellation of the task or preventing cancellation completely. The task may also return a value or raise a different exception.
Immediately after this method is called, cancelled() will not return True (unless the task was already cancelled). A task will be marked as cancelled when the wrapped coroutine terminates with a CancelledError exception (even if cancel() was not called).
So after cleanup your coroutine must raise CancelledError to be marked as cancelled.
Using an extra coroutine to stop the loop is not an issue because it is not cyclic and be done immediately after execution.
def main():
loop = asyncio.get_event_loop()
asyncio.ensure_future(listen_to_ipc_channel_layer())
for sig in (signal.SIGINT, signal.SIGTERM):
loop.add_signal_handler(sig, ask_exit)
loop.run_forever()
print("Close")
loop.close()
#asyncio.coroutine
def listen_to_ipc_channel_layer():
while True:
try:
print("Running")
yield from asyncio.sleep(0.1)
except asyncio.CancelledError as e:
print("Break it out")
raise e # Raise a proper error
# Stop the loop concurrently
#asyncio.coroutine
def exit():
loop = asyncio.get_event_loop()
print("Stop")
loop.stop()
def ask_exit():
for task in asyncio.Task.all_tasks():
task.cancel()
asyncio.ensure_future(exit())
if __name__ == "__main__":
main()

I had this message and I believe it was caused by garbage collection of pending task. The Python developers were debating whether tasks created in asyncio should create strong references and decided they shouldn't (after 2 days of looking into this problem I strongly disagree! ... see the discussion here https://bugs.python.org/issue21163)
I created this utility for myself to make strong references to tasks and automatically clean it up (still need to test it thoroughly)...
import asyncio
#create a strong reference to tasks since asyncio doesn't do this for you
task_references = set()
def register_ensure_future(coro):
task = asyncio.ensure_future(coro)
task_references.add(task)
# Setup cleanup of strong reference on task completion...
def _on_completion(f):
task_references.remove(f)
task.add_done_callback(_on_completion)
return task
It seems to me that tasks should have a strong reference for as long as they are active! But asyncio doesn't do that for you so you can have some bad surprises once gc happens and long hours of debugging.

The reasons this happens is as explained by #Yeray Diaz Diaz
In my case, I wanted to cancel all the tasks that were not done after the first finished, so I ended up cancelling the extra jobs, then using loop._run_once() to run the loop a bit more and allow them to stop:
loop = asyncio.get_event_loop()
job = asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)
tasks_finished,tasks_pending, = loop.run_until_complete(job)
tasks_done = [t for t in tasks_finished if t.exception() is None]
if tasks_done == 0:
raise Exception("Failed for all tasks.")
assert len(tasks_done) == 1
data = tasks_done[0].result()
for t in tasks_pending:
t.cancel()
t.cancel()
while not all([t.done() for t in tasks_pending]):
loop._run_once()

Graceful shutdown of asyncio coroutines

I'm currently having problems closing asyncio coroutines during the shutdown CTRL-C of an application. The following code is a stripped down version of what I have right now:
#!/usr/bin/env python
# -*- coding: UTF-8 -*-
import asyncio
import time
import functools
import signal
class DummyProtocol(asyncio.Protocol):
def __init__(self, *args, **kwargs):
self._shutdown = asyncio.Event()
self._response = asyncio.Queue(maxsize=1)
super().__init__(*args, **kwargs)
def connection_made(self, transport):
self.transport = transport
def close(self):
print("Closing protocol")
self._shutdown.set()
def data_received(self, data):
#data = b'OK MPD '
# Start listening for commands after a successful handshake
if data.startswith(b'OK MPD '):
print("Ready for sending commands")
self._proxy_task = asyncio.ensure_future(self._send_commands())
return
# saving response for later consumption in self._send_commands
self._response.put_nowait(data)
async def _send_commands(self):
while not self._shutdown.is_set():
print("Waiting for commands coming in ...")
command = None
# listen for commands coming in from the global command queue. Only blocking 1sec.
try:
command = await asyncio.wait_for(cmd_queue.get(), timeout=1)
except asyncio.TimeoutError:
continue
# sending the command over the pipe
self.transport.write(command)
# waiting for the response. Blocking until response is complete.
res = await self._response.get()
# put it into the global response queue
res_queue.put_nowait(res)
async def connect(loop):
c = lambda: DummyProtocol()
t = asyncio.Task(loop.create_connection(c, '192.168.1.143', '6600'))
try:
# Wait for 3 seconds, then raise TimeoutError
trans, proto = await asyncio.wait_for(t, timeout=3)
print("Connected to <192.168.1.143:6600>.")
return proto
except (asyncio.TimeoutError, OSError) as e:
print("Could not connect to <192.168.1.143:6600>. Trying again ...")
if isinstance(e, OSError):
log.exception(e)
def shutdown(proto, loop):
# http://stackoverflow.com/a/30766124/1230358
print("Shutdown of DummyProtocol initialized ...")
proto.close()
# give the coros time to finish
time.sleep(2)
# cancel all other tasks
# for task in asyncio.Task.all_tasks():
# task.cancel()
# stopping the event loop
if loop:
print("Stopping event loop ...")
loop.stop()
print("Shutdown complete ...")
if __name__ == "__main__":
loop = asyncio.get_event_loop()
cmd_queue = asyncio.Queue()
res_queue = asyncio.Queue()
dummy_proto = loop.run_until_complete(connect(loop))
for signame in ('SIGINT','SIGTERM'):
loop.add_signal_handler(getattr(signal, signame), functools.partial(shutdown, dummy_proto, loop))
try:
loop.run_forever()
except KeyboardInterrupt:
pass
finally:
loop.close()
what gives me the following output if CTRL-C is pressed:
Connected to <192.168.1.143:6600>.
Ready for sending commands
Waiting for commands coming in ...
Waiting for commands coming in ...
Waiting for commands coming in ...
Waiting for commands coming in ...
^CShutdown of DummyProtocol initialized ...
Closing protocol
Stopping event loop ...
Shutdown complete ...
Task was destroyed but it is pending!
task: <Task pending coro=<DummyProtocol._send_commands() running at ./dummy.py:45> wait_for=<Future pending cb=[Task._wakeup()]>>
Task was destroyed but it is pending!
task: <Task pending coro=<Queue.get() running at /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/queues.py:168> wait_for=<Future pending cb=[Task._wakeup()]> cb=[_release_waiter(<Future pendi...sk._wakeup()]>)() at /usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/tasks.py:344]>
Exception ignored in: <generator object Queue.get at 0x10594b468>
Traceback (most recent call last):
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/queues.py", line 170, in get
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 227, in cancel
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/futures.py", line 242, in _schedule_callbacks
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 447, in call_soon
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 456, in _call_soon
File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/asyncio/base_events.py", line 284, in _check_closed
RuntimeError: Event loop is closed
I'm not very experienced with asyncio, so I'm pretty sure that I'm missing something important here. What really gives me headaches is the part of the output after Shutdown complete .... Beginning with Task was destroyed but it is pending!, I have to admit that I have no idea what's going on. I had a look on other questions but couldn't get it to work. So, why is this code outputting stuff like Task was destroyed but it is pending! aso.and how can cleany close the coroutines?
Thank's for your help!

What does Task was destroyed but it is pending! mean?
If at the moment your program finished some of asyncio tasks still not finished, you'll get this warning. This warning is needed because some task that are running may not correctly free some resources.
There're two common ways to solve it:
You can wait while tasks finished themselves
You can cancel tasks and wait while them finished
Asyncio and blocking synchronous operations
Let's look at you code:
def shutdown(proto, loop):
print("Shutdown of DummyProtocol initialized ...")
proto.close()
time.sleep(2)
# ...
time.sleep(2) - this line won't give coroutines time to finished. It'll just freeze all your program for two second. Nothing will happen during this time.
It happens because your event loop is running in same process where you call time.sleep(2). You should never call long running synchronous operations this way in your asyncio programs. Please read this answer to see how async code works.
How can we wait tasks finished
Let's try to modify shutdown function. This is not async function, you can't await something inside it. To execute some async code we need to do it manually: stop currently running loop (since it's already running), create some async function to await tasks finished, pass this function to be executed in event loop.
def shutdown(proto, loop):
print("Shutdown of DummyProtocol initialized ...")
# Set shutdown event:
proto.close()
# Stop loop:
loop.stop()
# Find all running tasks:
# For python version < 3.7 use asyncio.Task.all_tasks()
# For python version >= 3.7 use asyncio.all_tasks()
pending = asyncio.Task.all_tasks()
# Run loop until tasks done:
loop.run_until_complete(asyncio.gather(*pending))
print("Shutdown complete ...")
You can also just cancel tasks and await them finished. See this answer for details.
Where to place clean up operations
I'm not too familiar with signals, but do you really need it to catch CTRL-C? Whenever KeyboardInterrupt happens it will thrown at the line where you run the event loop (in you code it's loop.run_forever()). I might be wrong here, but a common way to handle this situation is to place all cleanup operations in a finally block.
For example, you can see how aiohttp does it:
try:
loop.run_forever()
except KeyboardInterrupt: # pragma: no branch
pass
finally:
srv.close()
loop.run_until_complete(srv.wait_closed())
loop.run_until_complete(app.shutdown())
loop.run_until_complete(handler.finish_connections(shutdown_timeout))
loop.run_until_complete(app.cleanup())
loop.close()

To complete the accepted answer, you can use aiorun which handles this problem for you pretty well: https://github.com/cjrh/aiorun