Multi-process Structuring and the THOTH Operating System

This report explores the idea of structuring programs as many concurrent processes. It is based on work done in designing, implementing, and using the Thoth operating system. Thoth implements an ahstraction that provides facilities to make this type of structuring attractive, namely inexpensive processes, efficient interprocess communication, dynamic process creation and destruction, and groups of processes sharing a common address space. The Thoth abstraction is described, including measurements of its performance and comments on its portability. This abstraction is motivated by considering various design and implementation tradeoffs. Then, the design of multi-process programs is discussed, both in terms of general principles and by giving specific uses and examples to demonstrate the adequacy of the abstraction. Examples are drawn from the operating system and the Thoth text editor. Finally, the feasibility of verifying the system is considered. This is motivated by the desire to exploit the multi-process structure of the system to aid in verification. We conclude that structuring programs as multiple processes can have significant benefits, especially for programs that respond to asynchronous events.