Cloning by Accident: An Empirical Study of Source Code Cloning across Software Systems

Abstract

One of the key goals of open source development is the sharing of knowledge, experience, and solutions that pertain to a software system and its problem domain. Source code cloning is one way in which expertise can be reused across systems; cloning is known to have been used in several open source projects, such as the SCSI drivers of the Linux kernel [16] . In this paper, we discuss two case studies in which we performed clone detection and analysis on several open source systems within the same domain: we examined nine text editors written in C, and eight X-Windows window managers written in C and C++. To our surprise, we found little evidence of "true" cloning activity, but we did notice a significant number of "accidental" clones --- that is, code fragments that are similar due to the precise protocols they must use when interacting with a given API or set of libraries. We further discuss the nature of "true" versus "accidental" clones, as well as the details of our case studies