Perfecting preemption threshold scheduling for object-oriented real-time system design

Abstract

In spite of the proliferation of object-oriented design methodologies in contemporary software development, their application to real-time embedded systems has been limited because of the practitioner's conservative attitude toward handling timing constraints. In fact, this conservative attitude is well-grounded because traditional priority-based scheduling techniques cannot be straightforwardly integrated into them. The automated implementation from the object-oriented real-time designs usually incurs a large number of tasks which, under traditional priority-based scheduling techniques, does not scale well due to excessive preemption overheads. Recently, preemption threshold scheduling was introduced to reduce run-time multi-tasking overhead while improving schedulability by exploiting non-preemptibility as much as possible. Unfortunately, the preemption threshold scheduling cannot be directly adopted into the object-oriented design methods due to the lack of real-time synchronization.In this paper, we present the essential basis of real-time synchronization for preemption threshold scheduling. Specifically, we integrate the priority inheritance protocol, the priority ceiling protocol, and the immediate inheritance protocol into preemption threshold scheduling. We also provide their schedulability analyses. Consequently, the integrated scheme, which minimizes worst-case context switches, is appropriate for the automated implementation of real-time object-oriented design models.