Programming dynamically reconfigurable open systems with SALSA

Abstract

Applications running on the Internet, or on limited-resource devices, need to be able to adapt to changes in their execution environment at run-time. Current languages and systems fall short of enabling developers to migrate and reconfigure application sub-components at program-execution time.In this paper, we describe essential aspects of the design and implementation of SALSA, an actor-based language for mobile and Internet computing. SALSA simplifies programming dynamically reconfigurable, open applications by providing universal names, active objects, and migration. Moreover, SALSA introduces three language mechanisms to help programmers coordinate asynchronous, mobile computations: token-passing continuations, join continuations and first-class continuations.We provide some examples which illustrate how SALSA programs are not only dynamically reconfigurable and open, but also much more concise and easier to follow than comparable Java code. Furthermore, we provide empirical results which show SALSA's performance to be better than Java code using an actor library, and which illustrate the difference between local, local area, and wide area communication and migration. Finally, we discuss the implementation of our preprocessor which translates SALSA code into Java.