Executor cannot handle asyncio.sleep() in coroutine

Bug report

Required Info:

• Operating System:
  • Ubuntu 16.04 and Ubuntu 18.04
• Installation type:
  • source
• Version or commit hash:
  • be4bc88
• DDS implementation:
  • Fast-RTPS
• Client library (if applicable):
  • rclpy

Steps to reproduce issue

With a ROS 2 workspace built and sourced:

1. Create foo_service.py with the following content:

import asyncio

from example_interfaces.srv import AddTwoInts

import rclpy


async def add_two_ints_callback(request, response):
    response.sum = request.a + request.b

    await asyncio.sleep(1)

    print('Service request handled')

    return response


def main():
    rclpy.init()
    node = rclpy.create_node('foo_service')
    srv = node.create_service(AddTwoInts, 'add_two_ints', add_two_ints_callback)
    rclpy.spin(node)
    rclpy.shutdown()


if __name__ == '__main__':
    main()

1. Run the service:

    python3 foo_service.py
   

2. Run a service client:

    ros2 run examples_rclpy_minimal_client client
   

Expected behavior

Service call succeeds without error.

Actual behavior

Service server crashes from assertion error:

AssertionError: yield from wasn't used with future

Trace:

Traceback (most recent call last):
  File "service.py", line 27, in <module>
    main()
  File "service.py", line 22, in main
    rclpy.spin(node)
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/__init__.py", line 119, in spin
    executor.spin_once()
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/executors.py", line 573, in spin_once
    raise handler.exception()
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/task.py", line 207, in __call__
    self._handler.send(None)
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/executors.py", line 324, in handler
    await call_coroutine(entity, arg)
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/executors.py", line 282, in _execute_service
    response = await await_or_execute(srv.callback, request, srv.srv_type.Response())
  File "/home/jacob/ws/actions_ws/install/rclpy/lib/python3.5/site-packages/rclpy/executors.py", line 89, in await_or_execute
    return await callback(*args)
  File "service.py", line 11, in add_two_ints_callback
    await asyncio.sleep(1)
  File "/usr/lib/python3.5/asyncio/tasks.py", line 516, in sleep
    return (yield from future)
  File "/usr/lib/python3.5/asyncio/futures.py", line 362, in __iter__
    assert self.done(), "yield from wasn't used with future"
AssertionError: yield from wasn't used with future

Additional information

The error appears related to the call to asyncio.sleep(1) in the service server callback. If we replace it with time.sleep(1), the code executes without error.

[TheDelus]

Are there plans to support pythons async and await syntax in the future? Not beeing able to use pythons own system of coroutines and async execution is one of a the big things holding us back migrating to ROS2. With ROS1 we use the workaround provided by locusrobotics/aiorospy.

Sorry for hijacking this is issue, but it appears to be the most fitting place for my question.

[sloretz]

I’m not well-versed with the decision to define our own Future and Task classes, but perhaps it’s possible to replace them with equivalents in asyncio.

There are two standard modules for executors/tasks/futures: concurrent.futures which is thread safe but does not support coroutines, and asyncio which supports coroutines but is not threadsafe. The rclpy executor supports both multiple threads and coroutines, so it has to have its own 😦