Race condition: Goal state is SUCCEEDED before result is available.

[jorgenfb]

SimpleActionClient seems to have a race condition. Calling get_state() can give the SUCCEEDED state before a result is available.

This is a package showing the problem. It uses a SimpleActionClient to make a request and then checks client.get_state() at a high frequency to check for SUCCEEDED state and then checks if client.get_result() returns a result. An error is printed if the result is missing. It makes a maximum of 1000 requests to try to trigger this error. Run roslaunch action_client_breaker action_client_breaker.test and wait for a ERROR message in the console.
action_client_breaker.zip

BufferClient in tf2_ros was previously affected by this issue. See ros/geometry2#178.

[HappySamuel]

Hi @jorgenfb

I also faced this issue when i am calling client.get_state() at around 5Hz. Have you find a solution / workaround for this?

Best,
Samuel

[jorgenfb]

Yes, have a look at ros/geometry2#178. Especially this comment: ros/geometry2#178 (comment). You might be able to use:

your_simple_action_client.wait_for_result()

[HappySamuel]

Isn't the client.wait_for_result() will put whole system on wait? until result come out?

[jorgenfb]

Just your current thread. If you are only spinning until a result is ready, then you can use wait_for_result without any issue Regards Jørgen Borgesen nLink +47 456 19 649 The content of this e-mail is of a confidential and proprietary nature and may be protected by law. The content is only intended for the individual(s) named in the message. If you have received this e-mail by mistake, please reply to this message and delete the e-mail and its content afterwards. You may not copy or distribute any of the content in this e-mail.

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