Learning about concurrency and synchronization is difficult for novices. In prior work, we developed saUML, a refinement of UML sequence diagrams, to address these difficulties and found them to be beneficial when compared to text-only presentations. This paper compares saUML to standard UML sequence diagrams to judge their relative effectiveness in enhancing a novice programmer’s understanding of programs with different levels of synchronization complexity. One experiment compared the two notations when used to understand programs of low synchronization complexity, as judged by their use of only simple synchronization primitives, such as mutex locks. Here, a beneficial trend was observed, but it did not rise to the level of statistical significance. A second experiment compared the two notations on similar tasks but on programs with more complex synchronization constructs, in this case condition synchronization using primitives, such as wait and signal. Here, a significant benefit (p < 0.05) was found to exist.

While the sources of complexity in the initial design and verification of multi-threaded software systems are welldocumented, less is known of the issues specific to the maintenance of these systems. The literature contains a number of observational studies of programmers performing maintenance, conducted in the context of sequential software and designed to investigate the factors and behaviors that lead to success. To help fill the gap in knowledge in the area of concurrent software maintenance, we conducted a study that refines the findings of two prior studies, those of Littman et al. and of Vessey, to address issues and obstacles that arise in the understanding of concurrent software. We validated these refinements by observing programmers performing corrective maintenance on a small but complex multi-threaded server program. 1.

A comprehensive understanding of students ' common difficulties in understanding synchronization and concurrency is a prerequisite for developing tools and educational materials to alleviate these difficulties. In this paper we briefly present a study through which we identified students’ misconceptions about concurrency and synchronization, categorized their misunderstandings into a misconception pyramid, and built subject profiles through which we were able to discover the nature and frequency of the misconceptions exhibited by the students in this study. Based on these findings, we developed metrics to capture the breadth and severity of individual subject's misconceptions. We describe these metrics and show how they correlate with other measurements of understanding of concurrency and synchronization. 1.