The Unstoppable Orchestra: a responsive distributed application

Responsiveness, the ability to provide real-time behavior even in the presence of faults, is becoming one of the most sought after properties in distributed computing systems. We present a framework for "high-performance responsive computing" in networked systems whose current implementation works on a network of five NeXTSTEP (Mach 2.5)-based HP workstations. "The Unstoppable Orchestra" is a demonstration program which runs in our environment. This application simulates a real orchestra consisting of musicians playing different instrumental parts of a classical masterpiece. However instead of real musicians our orchestra consists of computers equipped with speakers. In contrast to the real orchestra, where a sudden disappearance of, for example, a flautist can hardly be hidden, in our orchestra one "musician" can take over his neighbour\´s part, ensuring uninterrupted performance. We discuss the design issues behind the "Unstoppable Orchestra" and show how our programming framework supports synchronization and reconfiguration of responsive applications.