How to obtain current queue capacity? [closed]

edit

Hi! I'm working with Kinect depth map through cv_bridge and have next problem: program subscribes on /camera/depth/image with next code:

image_transport::Subscriber imageSubscriber;

imageSubscriber = it.subscribe(topic.c_str(), queueSize /*=100*/, &DepthConverter::imageCallback, this);

For debug i'm really need in information, how many images in this time in the queue (there is complicated and time expensive work in callback, so, after some minutes, program fails to receive new message). Can I find somewhere this information?

Or, I should, as example, publish message to "/rosout" and use rostopic hz /mytopic?

Thanks for help in advance!