image_saver: Support lazy subscribing

[knorth55]

Move from #391

This pull request includes following updates:

• Support lazy subscribing input topic
• Subscribing image topic to be saved only when saving is requested.
• Add ~wait_for_save & ~save_timeout params
  • image_saver has three ways for saving images (though not yet documented)
    • Oneshot save by using ~save service
    • Durative save by using ~start & ~end service
    • Continuous save by setting ~save_all_image param
  • On oneshot way of saving, call of service ~save did never return until no image is published from publishers, which can lock calleeforever.
  • With ~wait_for_save param, we can switch whether calling ~save request blocks until image is saved or immediately returns from the request just like a non-blocking way.
  • If we choose the ~wait_for_save as true, then we can set ~save_timeout param to set timeout for waiting.

[knorth55]

Thank you for your review. I updated to follow your review. However, I'm wondering if this change is released in Kinetic or not. Kinetic is not EOL, and image_pipeline seems to not be released in Kinetic recently. Do you have any plan to release in Kinetic?

[knorth55]

Sorry it was my misunderstanding. We can use C++11 in kinetic, now I got it. https://www.ros.org/reps/rep-0003.html

[JWhitleyWork]

Also, please update the launch files.

[knorth55]

which launch file are you talking about?

[JWhitleyWork]

Nevermind on the launch files. I guess there are no examples in image_view.

[JWhitleyWork]

@knorth55 This has been hanging around for some time. Are you still able to work on it? If not, I can close the PR.

[mikeferguson]

Closing due to lack of response