How Do Developers Toggle Breakpoints? Observational Studies

One of the most important tasks in software maintenance is debugging. Developers perform debugging to fix faults and implement new features. Usually they use interactive development environments to perform their debugging sessions. To start an interactive debugging session, developers must set breakpoints. Choosing where to set breakpoints is a non-trivial task, yet few studies have investigated how developers set breakpoints during interactive debugging sessions. To understand how developers set breakpoints, we analysed more than 10 hours of 45 video-recorded debugging sessions, where a total of 307 breakpoints were set. We used the videos from two independent studies involving three software systems. We could observe that: (1) considerable time is spent by developers until they are able to set the first breakpoint; (2) when developers toggle breakpoints carefully, they complete tasks faster than developers who set (potential useless) breakpoints quickly; and (3) different developers set breakpoints in similar locations while working (independently) on the same tasks or different tasks. We discuss some implications of our observations for debugging activities.