The use of monitors for describing concurrency has been much discussed in the literature. When monitors are used in real systems of any size, however, a number of problems arise which have not been adequately dealt with: the semantics of nested monitor calls; the various ways of defining the meaning of WAIT; priority scheduling; handling of timeouts, aborts and other exceptional conditions; interactions with process creation and destruction; monitoring large numbers of small objects. These problems are addressed by the facilities described here for concurrent programming in Mesa. Experience with several substantial applications gives us some confidence in the validity of our solutions.

We have improved the performance of the Mach 3.0 operating system by redesigning its internal thread and interprocess communication facilities to use continuations as the basis for control transfer. Compared to previous versions of Mach 3.0, our new system consumes 85% less space per thread. Cross-address space remote procedure calls execute 14% faster. Exception handling runs over 60% faster. In addition to improving system performance, we have used continuations to generalize many control transfer optimizations that are common to operating systems, and have recast those optimizations in terms of a single implementation methodology. This paper describes our experiences with using continuations in the Mach operating system. 1 Introduction We have achieved significant improvements in the performance of the Mach 3.0 operating system kernel [Accetta et al. 86] by redesigning it to use continuations as the basis for control transfers between execution contexts. In our system, a thread b...

this paper was presented at the 7th ACM Symposium on Operating Systems Principles, Pacific Grove, Calif., Dec. 10-12, 1979

The first part of this paper provides rigorous definitions for several basic concepts underlying the design of dependable programs, such as specification, program semantics, exception, program correctness, robustness, failure, fault, and error. The second part investigates what it means to handle exceptions in modular programs structured as hierarchies of data abstractions. The problems to be solved at each abstraction level, such as exception detection and propagation, consistent state recovery and masking are examined in detail. Both programmed exception handling and default exception handling (such as embodied for example in recovery blocks or database transactions) are considered. An assessment of the adequacy of backward recovery in providing tolerance of software design faults is made. An earlier version of this paper was published in "Dependability of Resilient Computers", T. Anderson, Editor, BSP Professional Books, Blackwell Scientific Publications, UK, 1989, pp. 68-97 INTRO...

Abstract not found

The Mesa programming language supports program modularity in ways that permit subsystems to be developed separately but to be bound together with complete type safety. Separate and explicit interface definitions provide an effective means of communication, both between programs and between programmers. A configuration language describes the organization of a system and controls the scopes of interfaces. These facilities have had a profound impact on the way we design systems and Organize development projects. This paper reports our recent experience with Mesa, particularly its use in the development of an operating system. It illustrates techniques for designing interfaces, for using the interface language as a specification language, and for organizing a ~ystem to achieve the practical benefits of program modularity without sacrificing strict type-checking.

The experiences of Mesa's first users- primarily its implementers-are discussed, and some implications for Mesa and similar programming languages are sug-gested. The specific topics addressed are: module struc-ture and its use in defining abstractions, data-structur-ing facilities in Mesa, an equivalence algorithm for types and type coercions, the benefits of the type sys-tem and why it is breached occasionally, and the diffi-culty of making the treatment of variant records safe. Key Words and Phrases: programming languages, types, modules, data structures, systems programming

The use of monitors for describing concurrency has been much discussed in the literature. When monitors are used in real systems of any size, however, a number of problems arise which have not been adequately dealt with: the semantics of nested monitor calls; the various ways of defining the meaning of WAIT; priority scheduling; handling of timeouts, aborts and other exceptional conditions; interactions with process creation and destruction; monitoring large numbers of small objects. These problems are addressed by the facilities described here for concurrent programming in Mesa. Experience with several substantial applications gives us some confidence in the validity of our solutions.