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.