Capabilities

Implements the concept of capabilities as part of the robots-in-concert system.

Building

Build it in a catkin workspace or build it stand alone:

$ source /opt/ros/hydro/setup.bash
$ mkdir build
$ cd build
$ cmake ..
$ make
$ source ./devel/setup.bash

Running a demo

You can setup a demo of sorts using one of the test fixtures.

Starting the capability server

Start the capability server with the demo.launch file:

$ roslaunch capabilities demo.launch

This is equivalent to running a roscore and then this:

$ capability_server `rospack find capabilities`/test/discovery_workspaces/minimal

This starts the capability server which crawls the ROS_PACKAGE_PATH and looks for packages which export capabilities. In this case it should find the minimal package in the test/discovery_workspaces folder. You can look at the package.xml of minimal to see how it defines its capabilities:

<?xml version="1.0"?>
<package>
  ...
  <export>
    <capability_interface>
      interfaces/Minimal.yaml
    </capability_interface>
    <capability_provider>
      providers/minimal.yaml
    </capability_provider>
    <semantic_capability_interface>
      interfaces/SpecificMinimal.yaml
    </semantic_capability_interface>
    <capability_provider>
      providers/specific_minimal.yaml
    </capability_provider>

  </export>
</package>

It defines one capability interface, Minimal, and a semantic interface called SpecificMinimal. It also provides a capability provider for each of those interfaces. Looking at the Minimal interface spec file:

%YAML 1.1
---
name: Minimal
spec_version: 1
spec_type: interface
interface: {}

It basically fills out only the explicitly required fields (it's minimal after all).

You can also take a look at the minimal provider:

%YAML 1.1
---
name: minimal
spec_version: 1
spec_type: provider
implements: Minimal
launch_file: 'launch/minimal.launch'

You can see that this provider specifies that it implements the Minimal interface, and it has a launch file, which is specified relatively from the minimal spec file. This launch file simply runs a dummy script:

<launch>
    <node name="minimal" pkg="minimal_pkg" type="minimal.py" output="screen" />
</launch>

Which just prints and publishes a message periodically and then stops after 10 seconds:

#!/usr/bin/env python

import rospy
from std_msgs.msg import String


def minimal():
    pub = rospy.Publisher('chatter', String)
    rospy.init_node('minimal')
    start = rospy.Time.now()
    while not rospy.is_shutdown() and (rospy.Time.now() - start).to_sec() < 10:
        str = "hello world %s" % rospy.get_time()
        rospy.loginfo(str)
        pub.publish(String(str))
        rospy.sleep(1.0)


if __name__ == '__main__':
    try:
        minimal()
    except rospy.ROSInterruptException:
        pass

Testing out the capability server

Now there should be some key ROS services available:

$ rosservice list --nodes | grep /capability_server
/get_interfaces /capability_server
/get_providers /capability_server
/get_semantic_interfaces /capability_server
/reload_capabilities /capability_server
/start_capability /capability_server
/stop_capability /capability_server

You can call these services to query, start, and stop capabilities.

You can list the available interfaces:

$ rosservice call /get_interfaces
interfaces: ['Minimal']

You can also list the providers for an interface:

$ rosservice call /get_providers Minimal
providers: ['minimal']

Start one with this command line:

$ rosservice call /start_capability Minimal minimal
successful: True

This is telling the capability server to start the Minimal capability, preferring the minimal provider.

You can switch back to the capability_server and see that it is printing the message to the screen. After 10 seconds this node should shutdown normally, but you will get an error message like this:

[INFO] [WallTime: 1374023441.816336] Request to start capability 'Minimal' with provider 'minimal'
... logging to /Users/william/.ros/log/901417f8-ee7d-11e2-9b39-542696cef915/roslaunch-dosa-90541.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt

started roslaunch server http://dosa:54017/

SUMMARY
========

PARAMETERS
 * /rosdistro
 * /rosversion

NODES
  /
    minimal (minimal_pkg/minimal.py)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
process[minimal-1]: started with pid [90564]
[INFO] [WallTime: 1374023442.906086] hello world 1374023442.91
[INFO] [WallTime: 1374023443.907306] hello world 1374023443.91
[INFO] [WallTime: 1374023444.909204] hello world 1374023444.91
[INFO] [WallTime: 1374023445.911004] hello world 1374023445.91
[INFO] [WallTime: 1374023446.912970] hello world 1374023446.91
[INFO] [WallTime: 1374023447.914730] hello world 1374023447.91
[INFO] [WallTime: 1374023448.916598] hello world 1374023448.92
[INFO] [WallTime: 1374023449.918565] hello world 1374023449.92
[INFO] [WallTime: 1374023450.919426] hello world 1374023450.92
[INFO] [WallTime: 1374023451.921269] hello world 1374023451.92
[minimal-1] process has finished cleanly
log file: /Users/william/.ros/log/901417f8-ee7d-11e2-9b39-542696cef915/minimal-1*.log
all processes on machine have died, roslaunch will exit
shutting down processing monitor...
... shutting down processing monitor complete
done
[ERROR] [WallTime: 1374023453.342853] Capability Instance 'minimal' terminated unexpectedly, it was previously in the 'running' state.
[INFO] [WallTime: 1374023453.343502] Capability Provider 'minimal' for Capability 'Minimal' has terminated.

This is because from the capability_server's perspective the launch file it ran shutdown unexpectedly. This is normal for this launch file, but probably an error for most launch files which are designed to run forever, until stopped.

Stopping a capability

If you run the capability again:

$ rosservice call /start_capability Minimal minimal
successful: True

And then within 10 seconds call:

$ rosservice call /stop_capability Minimal
successful: True

The capability_server will preempt the provider currently running for the Minimal interface, if one is running. In this case we just launched the minimal provider so it will be shutdown prematurely:

[INFO] [WallTime: 1374018047.353614] Request to start capability 'Minimal' with provider 'minimal'
... logging to /Users/william/.ros/log/dc556d54-ee70-11e2-b171-542696cef915/roslaunch-dosa-89740.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt

started roslaunch server http://dosa:53279/

SUMMARY
========

PARAMETERS
 * /rosdistro
 * /rosversion

NODES
  /
    minimal (minimal_pkg/minimal.py)

ROS_MASTER_URI=http://localhost:11311

core service [/rosout] found
process[minimal-1]: started with pid [89763]
[INFO] [WallTime: 1374018048.422365] hello world 1374018048.42
[INFO] [WallTime: 1374018049.423824] hello world 1374018049.42
[INFO] [WallTime: 1374018050.425631] hello world 1374018050.43
[INFO] [WallTime: 1374018051.427550] hello world 1374018051.43
[INFO] [WallTime: 1374018052.428946] hello world 1374018052.43
[INFO] [WallTime: 1374018053.430748] hello world 1374018053.43
[INFO] [WallTime: 1374018054.432479] hello world 1374018054.43
[INFO] [WallTime: 1374018055.433698] hello world 1374018055.43
[INFO] [WallTime: 1374018055.752547] Request to stop capability 'Minimal'
[minimal-1] killing on exit
shutting down processing monitor...
... shutting down processing monitor complete
done
[INFO] [WallTime: 1374018056.651382] Capability Provider 'minimal' for Capability 'Minimal' has terminated.

These are the basics, more details about the specifications and chaining capabilities in the future.