Experience with Charlotte: simplicity and function in a distributed operating system

Abstract

A retrospective view is presented of the Charlotte distributed operating system, a testbed for developing techniques and tools to solve computation-intensive problems with large-grain parallelism. The final version of Charlotte runs on the Crystal multicomputer, a collection of VAX-11/750 computers connected by a local area network. The kernel/process interface is unique in its support for symmetric, bi-directional communication paths (called links), and synchronous nonblocking communications. Several lessons were learned in implementing Charlotte. Links have proven to be a useful abstraction, but the primitives do not seem to be at quite the right level of abstraction. The implementation uses finite-state machines and a multitask kernel, both of which work well. It also maintains absolute distributed information which is more expensive that using hints. The development of high-level tools, particularly the Lynx distributed programming language, has simplified the use of kernal primitives and helps to manage concurrency at the process level.