passing sensor_msgs::Image across different processes

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Hi All,

I have a working ROS program that contains two nodes:

1. usb_cam_node (/opt/ros/electric/stacks/bosch_drivers/usb_cam/src/usb_cam_node) , and

2. A node named B that processes videos with cv_bridge.

The basic logic of this program is simple:

1. usb_cam_node gets a video frame from the USB camera, and then publishes a message (of type sensor_msgs::ImageConstPtr& msg) onto a topic to which B subscribes;

2. B has a callback function that processes the frame upon receiving a message. This callback function looks like this:

   callbackB(const sensor_msgs::ImageConstPtr& msg){//Do image processing}

So far usb_cam_node and B are working fine on Ubuntu 10.10.

Now I plan to move the image processing part within callbackB(const sensor_msgs::ImageConstPtr& msg) to a real-time task spawned by Xenomai APIs within B. B and this real-time task, say, R, are two different processes, although R is spawned within B. In this new version, callbackB(const sensor_msgs::ImageConstPtr& msg) now only notifies R the receiving of msg and sends &msg to R. Once R have &msg, it is supposed to do the exactly same thing as the old version of callBackB() does. In my experiment, R can read some basic frame (image) info such as msg->height, which means R should get the correct (?) reference to the image via msg; However, the whole program crashes when cv_bridge::toCvCopy(msg, enc::BGR8); is called.

I am confused here: It seems R gets the correct reference to msg (i.e., &msg), as msg->height gets the correct value. Then why the whole program crashes when cv_bridge::toCvCopy(msg, enc::BGR8); is called? In GDB, I did notice something related to segment fault when this call is executed. Is this related to the fact that msg is a "smart pointer" instead of a normal C++ pointer? Did I wrongly assume that B and R have the same address space? (But then why R can read msg->height correctly?)

With Man Thanks,

Tom