Practical Application of the Ceiling Protocol in a Real-Time System

摘要

This position paper explores the application of a new priority management protocol for bringing a heretofore unknown level of response time predictability to the design of real-time programs in Ada. While the protocol is not itself dependent on the use of Ada, we believe that when used in an Ada design, it will enable a much more complete use of modern software engineering in the implementation of real-time software, enhancing not only performance, but also quality, reliability, and maintainability. Thus, the protocol helps to separate timing issues from the logical structure of a set of tasks, thereby helping to provide a better basis for engineering real-time software. This new protocol, called the ceiling protocol, is described in a companion position. Although the protocol provides what we believe are extremely important benefits to the design of real-time systems, it is not without cost; the ceiling protocol imposes several significant limitations on the use of Ada in software design. It is the purpose of this paper to explore some of the ramifications of these limitations, illustrating the issues raised by the use of an actual problem encountered in modern avionics systems. We hope to demonstrate the likelihood that, in spite of these limitations, there are many existing real-time problems which could greatly benefit from the application of this protocol. (kr)