Sometimes subscriptions lost messages from multiple publishers

[qiuzhong]

When there are multiple publisher nodes publishing messages simultaneously, sometimes the subscription seems to be blocking.

We need to investigate why some messages are lost. I'll provide more useful information with rclpy client.

[qiuzhong]

I did the same tests for rclpy version. The message losing also exists on for the rclpy version and the losing rate is even higher than rclnodejs client library.

[minggangw]

I suggest keeping an eye on this problem until the fist non-beta release of ROS arrives. If this phenomenon appears constantly then, I think we can submit an issue either for rclpy or rcl.

[Christywl]

I see the similar issue during the Client/Server testing.

multi-clients<-->one-service:

[minggangw]

Did you test this case on Ardent Apalone?

[Christywl]

Before that, I run the tests based on ros2/ros2@b12ebdc