The actionlib package provides a standardized interface for interfacing with
preemptible tasks. Examples of this include moving the base to a target
location, performing a laser scan and returning the resulting point cloud,
detecting the handle of a door, etc.

In any large ROS based system, there are cases when someone would like to send
a request to a node to perform some task, and also receive a reply to the
request. This can currently be achieved via ROS services.

In some cases, however, if the service takes a long time to execute, the user
might want the ability to cancel the request during execution or get periodic
feedback about how the request is progressing. The actionlib package provides
tools to create servers that execute long-running goals that can be
preempted. It also provides a client interface in order to send requests to the
server.