Add tips about service client and rate (#4132) (#4841)

* add tips about service client and rate Signed-off-by: Matthew Foran <[email protected]> Co-authored-by: Tomoya Fujita <[email protected]> Co-authored-by: Chris Lalancette <[email protected]> (cherry picked from commit 9f4d273) Co-authored-by: Matthew Foran <[email protected]>
ros2 · Oct 30, 2024 · 608d46f · 608d46f
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diff --git a/source/How-To-Guides/Migrating-from-ROS1/Migrating-Python-Packages.rst b/source/How-To-Guides/Migrating-from-ROS1/Migrating-Python-Packages.rst
@@ -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>`.
diff --git a/.../Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Service-And-Client.rst b/.../Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Service-And-Client.rst
@@ -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
 
@@ -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
 
@@ -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
 ~~~~~~~~~~~~~~~~~~~~~~