Unanticipated partial behavioral reflection: Adapting applications at runtime

Dynamic, unanticipated adaptation of running systems is of interest in a variety of situations, ranging from functional upgrades to on-the-fly debugging or monitoring of critical applications. In this paper we study a particular form of computational reflection, called unanticipated partial behavioral reflection (UPBR), which is particularly well suited for unanticipated adaptation of realworld systems. Our proposal combines the dynamicity of unanticipated reflection, i.e., reflection that does not require preparation of the code of any sort, and the selectivity and efficiency of partial behavioral reflection (PBR). First, we propose unanticipated partial behavioral reflection which enables the developer to precisely select the required reifications, to flexibly engineer the metalevel and to introduce the metabehavior dynamically. Second, we present a system supporting unanticipated partial behavioral reflection in Squeak Smalltalk, called GEPPETTO, and illustrate its use with a concrete example of a web application. Benchmarks validate the applicability of our proposal as an extension to the standard reflective abilities of Smalltalk.We acknowledge the financial support of the Swiss National Science Foundation for the project “Analyzing, capturing and taming software change” (SNF Project No. 200020-113342, October 2006–September 2008). É. Tanter is partially financed by the Millennium Nucleus Center for Web Research, Grant P04-067-F, Mideplan, Chile, as well as by FONDECYT Project 11060493