We have found many programming problems for which neither procedural nor object-oriented programming techniques are sufficient to clearly capture some of the important design decisions the program must implement. This forces the implementation of those design decisions to be scattered throughout the code, resulting in “tangled” code that is excessively difficult to develop and maintain. We present an analysis of why certain design decisions have been so difficult to clearly capture in actual code. We call the properties these decisions address aspects, and show that the reason they have been hard to capture is that they crosscut the system’s basic functionality. We present the basis for a new programming technique, called aspect-oriented programming, that makes it possible to clearly express programs involving such aspects, including appropriate isolation, composition and reuse of the aspect code. The discussion is rooted in systems we have built using aspect-oriented programming.

Two of the most important issues in distributed systems are the synchronization of concurrent threads and the application-level data transfers between execution spaces. At the design level, addressing these issues typically requires analyzing the components under a different perspective than is required to analyze the functionality. Very often, it also involves analyzing several components at the same time, because of the way those two issues cross-cut the units of functionality. At the implementation level, existing programming languages fail to provide adequate support for programming in terms of these different and cross-cutting perspectives. The result is that the programming of synchronization and remote data transfers ends up being tangled throughout the components code in more or less arbitrary ways. This thesis presents a language framework called D that untangles the implementation of synchronization