Add information on controller's joint usage (ros ticket #4258)

[ahendrix]

When a node switches controllers, it must be aware of all conflicts between controllers. This ticket describes a method of reporting joint usage by the controllers so that the conflicts can be discovered automatically.

There are a few options for reporting joint usage by the controller:

1. Each controller provides a service which lists what joints it uses.
2. Each controller overloads a function getClaimedJoints(), which the Controller Manager calls. The CM provides a service for querying all the controllers.
3. Each controller calls a function registerJointClaims() on the CM, which stores the list of claims. The CM provides a service for returning the current list of claims.

Option 1 was nixed because it requires the user to discover and make a dozen service calls to determine the conflicts. Option 3 requires exposing a function from the CM to the controllers. This requires more intensive changes than option 2.

In option 2, the CM provides a service for querying the joints that each controllers will claim. Here's a proposed version of that service:

{{{

[ListControllerClaims]

ControllerClaim[] claims
string controller_name
bool is_running
string[] joints
}}}

When the service is called, the CM will call getClaimedJoints() on each controller and return the aggregated result. The result includes the information necessary to determine which controllers conflict with the desired set.

trac data:

• Owner: sglaser
• Reporter: sglaser
• Reported at: Thu Apr 29 12:13:57 2010
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/4258