Task communication in DEMOS

Abstract

This paper describes the fundamentals and some of the details of task communication in DEMOS, the operating system for the CRAY-1 computer being developed at the Los Alamos Scientific Laboratory. The communication mechanism is a message system with several novel features. Messages are sent from one task to another over links. Links are the primary protected objects in the system; they provide both message paths and optional data sharing between tasks. They can be used to represent other objects with capability-like access controls. Links point to the tasks that created them. A task that creates a link determines its contents and possibly restricts its use. A link may be passed from one task to another along with a message sent over some other link subject to the restrictions imposed by the creator of the link being passed. The link based message and data sharing system is an attractive alternative to the semaphore or monitor type of shared variable based operating system on machines with only very simple memory protection mechanisms or on machines connected together in a network.

References

1. 1 Brinch Hansen, P.Operating System Principles. Prentice-Hall, Englewood Cliffs, N.J., 1973.
2. 2 Dijkstra, E. W. Cooperating sequential processes. in Programming Languages (F. Genuys, ed.). Academic Press (1968), 43-112.
3. 3 Fabry, R. S. Capability-based addressing. Communications of the ACM 17, 7 (July 1974), 403-412.
4. 4 Hoare, C. A. R. Monitors: an operating system structuring concept. Communications of the ACM 17, 10 (Oct. 1974), 549-557. Corrigendum, Communications of the ACM 18, 2 (Feb. 1975), 95.
5. 5 Howard. J. H. Mixed Solutions to the Deadlock Problem. Communications of the ACM 16, 7 (July 1973), 427-430.
6. 6 Lampson, B. W. and Sturgis, H. E. Reflection on an Operating System Design. Communications of the ACM 19, 5 (May 1976), 251-265.
7. 7 Morris, J. H. Protection in programming languages Communications of the ACM 16, 1 (Jan. 1973), 15-21.

Index Terms

• Information systems

  • Information storage systems

    • Storage management

• Security and privacy

  • Systems security

    • Operating systems security

• Social and professional topics

  • Professional topics

    • Management of computing and information systems

      • Project and people management

        • Systems development

• Software and its engineering

  • Software organization and properties

    • Contextual software domains

      • Operating systems

        • Communications management

          • Message passing

        • File systems management

        • Memory management