Added new functionality: service_is_available

[richiprosima]

This PR contains the service_is_available functionality. To work properly Fast-RTPS has to be in/after commit eProsima/Fast-DDS@24825bb.

Closes #14.

[dirk-thomas]

@richiprosima The latest changes in FastRTPS introduced new compiler warnings and test failures. I think you should consider using Travis / AppVeyor to test the codebase automatically. I filled eProsima/Fast-DDS#62 for this but it applies to all repositories.

[richiprosima]

Your nightly CI job started while I was developing this new functionality. It checked out a commit which is not the final commit of my work. Sorry for that, I shouldn't have worked with master branch of Fast-RTPS.
Currently we have an internal Jenkins server for testing Fast-RTPS and other projects. In future we think about Travis. Thanks for your suggestion.

[wjwwood]

I'm testing this out right now. I believe we'll need to remove some test exclusions if this starts working:

ros2/examples#113
ros2/system_tests#143

If this works ok, I'll add pr's with the same branch name as this one that remove the test exclusions and/or sleeps so that we can run CI.

[wjwwood]

This is looking ok, but what's missing is graph notifications from fastrtps. What this means is that the blocking call wait_for_service will always only check the state of the services (with service_is_available) once. The intention is that it checks each time the graph changes, but that's not currently happening.

I'm looking into what's missing for that to start working. Based on how far off that functionality is, I'll recommend whether or not to merge this as an incremental improvement or to wait and get the graph change notifications in place first.

[wjwwood]

Looks like it is going to be easy to piggy-back the changes to support graph change notifications on top of the changes you made here to support service_is_available. I'll update this pr with my changes asap.

[wjwwood]

With d7b9634, the "add two ints" client/service examples work really well with each other. I'm going to continue digging into what needs to be done to re-enable all the appropriate tests.

[wjwwood]

Starting CI (fastrtps only):

• Linux:
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• OS X:
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• Windows:
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[wjwwood]

I'm rerunning CI (still fastrtps only) since I removed an extra sleep that @dhood found:

• Linux:
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• OS X:
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• Windows:
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[wjwwood]

Actually, all those were invalid because the rclcpp examples were not correctly enabled (I enabled them in a different way locally):

• Linux:
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• OS X:
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• Windows:
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[wjwwood]

Ok, the last ones definitely had the new rclcpp examples test for fastrtps:

http://ci.ros2.org/job/ci_linux/1729/testReport/(root)/test_add_two_ints_server_add_two_ints_client__rmw_fastrtps_cpp_/test_executable/

[wjwwood]

Ok, I've got passing CI with fastrtps and Connext now that I removed the system_tests pr from this group:

• Linux:
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• OS X:
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• Windows:
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This pr and the related pr on the examples repository are ready for review and merge.

[dhood]

Making it more explicit: system_tests using services, when re-enabled for both fastrtps and connext in ros2/system_tests#162, worked fine for fastrtps, just not connext (e.g. http://ci.ros2.org/job/ci_linux/1731/testReport/(root)/test_client_scope_cpp__rmw_fastrtps_cpp_/test_client_scope_cpp/)
so I would say it looks good