Add mutex to make Sensor::SetActive threadsafe

[iche033]

The IsActive function in the Sensor class is being called from various threads, e.g. rendering, physics (event callback from physics), and transport threads. So a mutex is added to protects calls for setting the active variable in Sensor class so that it is safe to call SetActive from gazebo plugins, e.g. various plugins in gazebo_ros_pkgs calls SetActive to enable / disable the sensors when subscriber count changes.

Signed-off-by: Ian Chen ichen@osrfoundation.org

[ahcorde]

LGTM

[chapulina]

LGTM. I'm just wondering if the access to active inside Sensor::Fini also needs to be protected, since that's a public function.

[iche033]

yep added mutex in Fini just in case. 59a5f75