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

Abstract

This paper presents a retrospective view 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-111750 computers connected by a local-area network. The kernellprocess interface is unique in its support for symmetric, bidirectional communication paths (called links), and synchronous nonblocking communication. Our experience indicates that the goals of simplicity and function are not easily achieved. Simplicity in particular has dimensions that conflict with one another. Although our design decisions produced a high-quality environment for research in distributed applications, they also led to unexpected implementation costs and required high-level language support. We learned several lessons from implementing Charlotte. Links have proven to be a useful abstraction, but our primitives do not seem to be at quite the right level of abstraction. Our implementation employed finite-state machines and a multitask kernel, both of which worked well. It also maintains absolute distributed information, which is more expensive than using hints. The development of high-level tools, particularly the Lynx distributed programming language, has simplified the use of kernel primitives and helps to manage concurrency at the process level.

Markov Teams ? An analytical approach to process migration in distributed computing systems

“…2 For the definition and a description of implementations of distributed operating systems see e.g. Tanenbaum, van Renesse (1985), Cheriton (1988) or Finkel et al (1989).…”

Kernel‐Kernel communication in a shared‐memory multiprocessor

“…the vertical organization is likely to perform better on a machine with uniform memory [7]. 1be horizontal crganizatlon may be easier to debug [10]. Most Unix kernels are vertical Demos [4] and Minix [21] are horizontal.…”

The Lynx distributed programming language: Motivation, design and experience

“…Motivation for Lynx grew out of experience with the Charlotte distributed operating system [2,12]. Like many other systems developed in the 1970's and early 1980's, Charlotte was designed to provide many of its services in user-level processes, rather than in the kernel.…”

“…Motivation for Lynx is discussed in section 2. Lynx was developed at the University of Wisconsin, where it was first implemented on the Charlotte multicomputer operating system [2,12]. Charlotte was designed without Lynx, but experience with a conventional library interface to the kernel suggested that language support for communication could make the programmer's life much easier.…”