search

osrf / capabilities

Implements the concept of capabilities as part of the robots-in-concert system.
Other
8 stars 26 forks source link

Discussion: How to prevent erroneous free'ing of capabilities #75

Open wjwwood opened 10 years ago

wjwwood commented 10 years ago

This is copied from https://github.com/osrf/capabilities/pull/70#issuecomment-47108222:

Ideally, the client should not get into the situation where it asks to stop/free an already stopped/freed cap.

In the current case the rapp rocon_apps/robot_teleop depends on both the RGBDSensor and the DifferentialMobileBase cap. However, down the dependency tree of the RGBDSensor cap there is also the dependency on the DifferentialMobileBase cap. Stopping the DifferentialMobileBase cap would now also stop all caps depending on it. And here there might be an error.

The app manager does not stop, but free the capabilities. So when the rapp is stopped, it first frees the DifferentialMobileBase cap.

[INFO] [WallTime: 1403701919.301008] Rapp Manager : stopped rapp [rocon_apps/teleop]'. [INFO] [WallTime: 1403701919.301422] Rapp Manager : Stopping required capabilities. [INFO] [WallTime: 1403701919.306375] Request to free usage of capability 'std_capabilities/DifferentialMobileBase' (bond id 'eb8e9780-fc63-11e3-a9ca-f46d04929542') And the cap server responds:

[INFO] [WallTime: 1403701919.306902] Capability 'std_capabilities/DifferentialMobileBase' being stopped because it has zero references However, at this point the RGBDSensor cap should still have an indirect dependency on it.

[INFO] [WallTime: 1403701919.307257] Capability 'turtlebot_capabilities/robot_state_publisher' being stopped because its dependency 'std_capabilities/DifferentialMobileBase' is being stopped. [INFO] [WallTime: 1403701919.307622] Capability 'turtlebot_capabilities/turtlebot2_bringup' being stopped because its dependency 'std_capabilities/RobotStatePublisher' is being stopped. [INFO] [WallTime: 1403701919.307938] Capability 'turtlebot_capabilities/rgbd_sensor' being stopped because its dependency 'turtlebot_capabilities/TurtleBotBringup' is being stopped. [INFO] [WallTime: 1403701921.447684] Capability Provider 'turtlebot_capabilities/rgbd_sensor' for Capability 'std_capabilities/RGBDSensor' has terminated. [INFO] [WallTime: 1403701922.014306] Capability Provider 'turtlebot_capabilities/turtlebot2_bringup' for Capability 'turtlebot_capabilities/TurtleBotBringup' has terminated. [INFO] [WallTime: 1403701922.014992] Stopping the 'turtlebot_capabilities/diagnostics' provider of the 'std_capabilities/Diagnostics' interface, because it has no dependents left. [INFO] [WallTime: 1403701922.015352] Rapp Manager : Stopped required capability 'std_capabilities/DifferentialMobileBase'. [INFO] [WallTime: 1403701922.019269] Request to free usage of capability 'std_capabilities/RGBDSensor' (bond id 'eb8e9780-fc63-11e3-a9ca-f46d04929542') [WARN] [WallTime: 1403701922.019799] RuntimeError: Cannot free Capability 'std_capabilities/RGBDSensor', because it is not running [INFO] [WallTime: 1403701922.020218] Rapp Manager : Stopped required capability 'std_capabilities/RGBDSensor'. [INFO] [WallTime: 1403701922.020605] Rapp Manager : All required capabilities have been stopped. Do you have a test case covering this situation?

With this in mind it might be better to revert this exception to an error. Currently can't think of a situation, where freeing a capability would throw this exception and it would be expected ... then again its already late over here. :-)

I decided to go ahead and merge #70 and open this issue for further discussion on the follow up topic described above.