Dear ros-users,

This is about the filter_chain.
Inside the callback function of the scan_to_scan_filter_chain, it calls the update function of the filter_chain.
In the update function of the filter_chain, each update function of the included filters is sequentially called.
However, I feel that if many filters are included in the scan_to_scan_filter_chain, this may cause not to receive any callbacks until you are done with all the filter updates. 

Please correct me if I am wrong.

The above I used as an example. Anyway, what I am trying to do is to publish some processed data after subscribing to a topic (laser scan). However, if I do the processing and publishing inside the callback of the subscription it may lead to block the callback. Please guide me how I should handle this.
I would like to know how spawning a new thread be done so that processing can be done separately without blocking the callback.

Thank you in advance.
Peshala