Research summary, January 1989 - June 1990

The Research Institute for Advanced Computer Science (RIACS) was established at NASA ARC in June of 1983. RIACS is privately operated by the Universities Space Research Association (USRA), a consortium of 62 universities with graduate programs in the aerospace sciences, under a Cooperative Agreement with NASA. RIACS serves as the representative of the USRA universities at ARC. This document reports our activities and accomplishments for the period 1 Jan. 1989 - 30 Jun. 1990. The following topics are covered: learning systems, networked systems, and parallel systems

An Architecture for the Compilation of Persistent Polymorphic Reflective Higher-Order Languages

Persistent Application Systems are potentially very large and long-lived application systems which use information technology: computers, communications, networks, software and databases. They are vital to the organisations that depend on them and have to be adaptable to organisational and technological changes and evolvable without serious interruption of service. Persistent Programming Languages are a promising technology that facilitate the task of incrementally building and maintaining persistent application systems. This thesis identifies a number of technical challenges in making persistent programming languages scalable, with adequate performance and sufficient longevity and in amortising costs by providing general services. A new architecture to support the compilation of long-lived, large-scale applications is proposed. This architecture comprises an intermediate language to be used by front-ends, high-level and machine independent optimisers, low-level optimisers and code generators of target machine code. The intermediate target language, TPL, has been designed to allow compiler writers to utilise common technology for several different orthogonally persistent higher-order reflective languages. The goal is to reuse optimisation and code-generation or interpretation technology with a variety of front-ends. A subsidiary goal is to provide an experimental framework for those investigating optimisation and code generation. TPL has a simple, clean type system and will support orthogonally persistent, reflective, higher-order, polymorphic languages. TPL allows code generation and the abstraction over details of the underlying software and hardware layers. An experiment to build a prototype of the proposed architecture was designed, developed and evaluated. The experimental work includes a language processor and examples of its use are presented in this dissertation. The design space was covered by describing the implications of the goals of supporting the class of languages anticipated while ensuring long-term persistence of data and programs, and sufficient efficiency. For each of the goals, the design decisions were evaluated in face of the results

Spray: programming with a persistent distributed heap

We introduce a programming paradigm for distributed applications based on a persistent distributed heap. A proof-of-concept implementation is provided as a Javascript library, together with several examples that embody popular patterns for web applications

Models of higher-order, type-safe, distributed computation over autonomous persistent object stores

A remote procedure call (RPC) mechanism permits the calling of procedures in another address space. RPC is a simple but highly effective mechanism for interprocess communication and enjoys nowadays a great popularity as a tool for building distributed applications. This popularity is partly a result of their overall simplicity but also partly a consequence of more than 20 years of research in transpaxent distribution that have failed to deliver systems that meet the expectations of real-world application programmers. During the same 20 years, persistent systems have proved their suitability for building complex database applications by seamlessly integrating features traditionally found in database management systems into the programming language itself. Some research. effort has been invested on distributed persistent systems, but the outcomes commonly suffer from the same problems found with transparent distribution. In this thesis I claim that a higher-order persistent RPC is useful for building distributed persistent applications. The proposed mechanism is: realistic in the sense that it uses current technology and tolerates partial failures; understandable by application programmers; and general to support the development of many classes of distributed persistent applications. In order to demonstrate the validity of these claims, I propose and have implemented three models for distributed higher-order computation over autonomous persistent stores. Each model has successively exposed new problems which have then been overcome by the next model. Together, the three models provide a general yet simple higher-order persistent RPC that is able to operate in realistic environments with partial failures. The real strength of this thesis is the demonstration of realism and simplicity. A higherorder persistent RPC was not only implemented but also used by programmers without experience of programming distributed applications. Furthermore, a distributed persistent application has been built using these models which would not have been feasible with a traditional (non-persistent) programming language