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Add tips about service client and rate (backport #4132) #4840

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Oct 30, 2024
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Add tips about service client and rate (backport #4132) #4840

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5 changes: 5 additions & 0 deletions source/How-To-Guides/Migrating-from-ROS1/Migrating-Python-Packages.rst
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Expand Up @@ -170,3 +170,8 @@ In ROS 2:
node.get_logger().info('service not available, waiting again...')
resp = add_two_ints.call_async(req)
rclpy.spin_until_future_complete(node, resp)

.. warning::

Do not use ``rclpy.spin_until_future_complete`` in a ROS 2 callback.
For more details see the :doc:`sync deadlock article <../Sync-Vs-Async>`.
8 changes: 6 additions & 2 deletions .../Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Service-And-Client.rst
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Expand Up @@ -246,7 +246,7 @@ Finally it creates a new ``AddTwoInts`` request object.
self.get_logger().info('service not available, waiting again...')
self.req = AddTwoInts.Request()

Below the constructor is the ``send_request`` method, which will send the request and return a future that can be passed to ``spin_until_future_complete``:
Below the constructor is the ``send_request`` method, which will send the request and spin until it receives the response or fails.

.. code-block:: python

Expand All @@ -255,7 +255,7 @@ Below the constructor is the ``send_request`` method, which will send the reques
self.req.b = b
return self.cli.call_async(self.req)

Finally we have the ``main`` method, which constructs a ``MinimalClientAsync`` object, sends the request using the passed-in command-line arguments, calls ``spin_until_future_complete``, and logs the results:
Finally we have the ``main`` method, which constructs a ``MinimalClientAsync`` object, sends the request using the passed-in command-line arguments, calls ``rclpy.spin_until_future_complete`` to wait for the result, and logs the results.

.. code-block:: python

Expand All @@ -273,6 +273,10 @@ Finally we have the ``main`` method, which constructs a ``MinimalClientAsync`` o
minimal_client.destroy_node()
rclpy.shutdown()

.. warning::

Do not use ``rclpy.spin_until_future_complete`` in a ROS 2 callback.
For more details see the :doc:`sync deadlock article <../../../How-To-Guides/Sync-Vs-Async>`.

3.2 Add an entry point
~~~~~~~~~~~~~~~~~~~~~~
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