We look at one important category of distributed applications characterized by the existence of multiple collaborating, and competing, components sharing mutable, long-lived, replicated objects. The problem addressed by this work is that of object state synchronization among the components. As an organizing principle for replicated objects, we formally specify the Global Object Tracker (GOT) model, an object-oriented programming model based on causal consistency whose elements and interfaces mirror those found in decentralized version control systems: a version graph, working data, diffs, commit, checkout, fetch, push, and merge. We have implemented GOT in a framework called Spacetime, written in Python.

In its purest form, GOT is impractical for real systems, because of the unbounded growth of the version graph and because passing diff'ed histories over the network makes remote communication too slow. I will talk about our solution to these problems that adds some constraints to GOT applications, but that makes the model feasible in practice. Additionally, I will show a performance analysis of Spacetime for a representative workload, which shows that the additional constraints added to GOT make it not just feasible, but that it makes good use of network resources.

This work is in collaboration with PhD candidate Rohan Achar, with previous contributions by former PhD student Dr. Arthur Valadares.

Cristina Videira Lopes is a Professor of Informatics in the School of Information and Computer Sciences at the University of California, Irvine, and is the Faculty Director of the professional Master of Software Engineering (MSWE) program. Her research focuses on programming and software engineering for large-scale data and systems. Early in her career, she was a founding member of the team at Xerox PARC that developed Aspect-Oriented Programming. Along with her research program, she is also a prolific software developer. Her open source contributions include being one of the core developers of OpenSimulator, a virtual world server. She is also a founder and consultant of Encitra, a company specializing in online virtual reality for early-stage sustainable urban redevelopment projects. Her book "Exercises in Programming Style" has gained rave reviews, including being chosen as "Notable Book" by the ACM Best of Computing reviews. She has a PhD from Northeastern University, and MS and BS degrees from Instituto Superior Tecnico in Portugal. She is the recipient of several National Science Foundation grants, including a prestigious CAREER Award. She claims to be the only person in the world who is both an ACM Distinguished Scientist and Ohloh Kudos Rank 9.

Iftekhar Ahmed is an Assistant Professor in the Department of Informatics in the Donald Bren School of Information and Computer Sciences at the University of California, Irvine. His general research interests are in the field of software engineering, with a focus on combining testing, static analysis and machine learning approaches to help improve software quality under real-world conditions. Ahmed received his Ph.D. from Oregon State University after working in the industry for 4 years. Before that, he earned his B.Sc. in Computer Science and Engineering from Shahjalal University of Science and Technology, Bangladesh.