Replacing passive tasks with Ada9X protected records

ABSTRACT

Ada 83 has often been criticized for its lack of a lightweight data synchronization primitive. Compiler vendors have responded to this criticism by implementing the Haberman-Nassi algorithm with a construct called a passive task. The Ada 9X Project has proposed a change to the Ada language adding a protected record construct to support lightweight synchronization. In this paper, we illustrate the changes in coding required to convert an application originally designed to exploit passive tasking to use the protected record construct instead. The resulting software engineering effects of using passive tasks and protected recordsre then compared for this sample task set. We conclude by discussing some protected recorded semantics that may require further clarification and/or modification, and some of the trade-offs that result.

REFERENCES

• 1: [1] A. Nico Habermann and Issac R. Nassi Efficient Implementation of Ada Tasks, Carnegie Mellon University, Department of Computer Science, CMU-CS-80-103, 1980.
• 2: Gary Frankel, Improving Ada tasking performance, Proceedings of the first international workshop on Real-time Ada issues, p.47-48, May 13-15, 1987, Morehampstead, Devon, United Kingdom
• 3: Kenneth Elsom, Asynchronous communication in Ada, Proceedings of the third international workshop on Real-time Ada issues, p.57-65, May 1989, Farmington, Pennsylvannia, United States
• 4: T. Baker, Opening up Ada-tasking, Proceedings of the fourth international workshop on Real-time Ada issues, p.60-64, July 16-20, 1990, Pitlochry, Perthshir, Scotland
• 5: K. C. Elsom, Prioritized asynchronism in Ada 9X, Proceedings of the fourth international workshop on Real-time Ada issues, p.103-110, July 16-20, 1990, Pitlochry, Perthshir, Scotland
• 6: [6] Robert A. Duff, Offer Pazy, and William A. White, "Lightweigth Task Synchronization: The Protected Record Mechanism in Ada 9X" TRI-Ada '91 Conference Proceedings. October 1991. Attachment to Proceedings.
• 7: [7] Ada 9X Mapping/Revision Team, Ada 9X Mapping, Volume II, Mapping Specification Office of the Under Secretary of Defense for Acquisition, December 1991. Version 4.0.
• 8: C. D. Locke , D. R. Vogel , T. J. Mesler, Predictable real-time avionics design using Ada tasks and Rendezvous study, Proceedings of the fourth international workshop on Real-time Ada issues, p.118-125, July 16-20, 1990, Pitlochry, Perthshir, Scotland
• 9: Lui Sha , John B. Goodenough, Real-Time Scheduling Theory and Ada, Computer, v.23 n.4, p.53-62, April 1990 [doi>10.1109/2.55469]
• 10: [10] C. Douglass Locke, Dave Vogel, Lee Lucas, and John B. Goodenough, Generic Avionics Software Specification, Software Engineering Institute, Carnegie Mellon University, CMU/SEI-90-TR-8, December 1990.
• 11: A. Burns , A. J. Wellings, In support of the Ada 9X real-time facilities, ACM SIGAda Ada Letters, v.XII n.1, p.53-64, Jan./Feb. 1992 [doi>10.1145/141454.141463]
• 12: [12] Ted Baker and Offer Pazy, "Real-Time Features for Ada 9X," Proceeding of the Twelfth IEEE Real-Time Systems Symposium, pp. 172-180, December 1991.

INDEX TERMS

Primary Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.2 Language Classifications

          Nouns: Ada

Additional Classification:
  D. Software
  D.3 PROGRAMMING LANGUAGES
      D.3.0 General
          Subjects: Standards
      D.3.3 Language Constructs and Features

General Terms:
Languages, Standardization