Designing Reusable Realtime Frameworks
Realtime application domains are, of course, characterized by tight,
demanding performance and timing constraints. Realtime programmers
often must also contend with highly dynamic (even volatile) software
requirements (i.e. requirements that are changing frequently). Some realtime
applications may also require complex, highly interactive user interfaces that
must be tightly coupled with their underlying application programs.
The strengths of object-oriented approaches in the realm of user interface
construction are well-documented. Perhaps less well understood is the manner
in which the application of object-oriented techniques can help one contend
with the complex lifecycle requirements present in many realtime application
domains. This question is the focus of [Foote 1988].
The work therein describes the design of a (simulated)
Smalltalk-80 application framework
for a family of realtime psychophysiological data acquisition and
experimental control applications. It shows how a well-constructed framework
can subsume the role played by skeleton programs in such application domains.
It documents the emergence both of this framework, and of a collection of
reusable application specific utility objects, including user interface components.
Frameworks and reusable class design are discussed in [Johnson & Foote 1988].
The resuse of proven, verified components is one way to deal with mission criticality
concerns.
This work was based on an earlier realtime system (the CPL Battery)
consructed using a Fortran preprocessor and object-oriented techniques. (See
[Heffley et. al. 1985]. My experience with these two systems has convinced me that
the benefits of applying object-oriented tools and techniques in realtime
domains can be considerable indeed.
It is difficult to generalize about how to address realtime performance
questions, since performance requirements vary widely from one application
to the next. Realtime designers have become quite adept at finding
pragmantic solutions to such concerns on an application-by-application basis.
Among such approaches to object-oriented performance questions are:
The use of hybrid object-oriented languages (such as C++)
The use of custom primitives in languages such as Smalltalk
Increased use of multiple threads and processors
Factoring realitme programs into multiple parallel objects in an object-oriented
environment can greatly increase the reuse potential of such objects,
since incidental sequential dependencies in the code are reduced.
See Confessions of a Framework Zealot
for some more recent reflections on the art and craft of constructing realtime object-oriented frameworks.
-- BF 2/26/98
References
[Foote 1998]
Brian Foote
Designing to Facilitate Change with Object-Oriented Frameworks
Masters Thesis, 1988
University of Illinois at Urbana-Champaign
[Heffley et. al. 1985]
Earle Heffley, Brian Foote, Tony Mui, and Emanuel Donchin
Pearl II: Portable Laboratory System Psychophysiological Assessment using Event Related Brain Potentials
Neurobehavioral Toxicology and Teratology
Volume 7, pp. 399-407, 1985
[Johnson & Foote 1988]
Ralph E. Johnson and Brian Foote
Designing Reusable Classes
Journal of Object-Oriented Programming
Volume 1, Number 2, June/July 1988
pages 22-35
Brian Foote foote@cs.uiuc.edu
Last Modified: 23 April 2004