Strategies for handling the activity problem in runtime software evolution by reducing activity

Runtime software evolution means updating software systems while they are running, something that is useful for systems with high availability requirements. A method is active if it has been called and not yet finished its execution, i.e. it has an activation record on at least one method call stack. Activity is a problem when making runtime updates, since it must be decided how the activation records of updated methods shall be treated. When inactive methods are updated, it is reasonable to have the system run the version of the methods next time they are called. The main goal of this paper is to describe different strategies to reduce the activity and under which circumstances those strategies are viable. To do so we define some properties of active methods in order to facilitate an abstract view on different kinds of activity.