Execution Stack Management for Hard Real-Time Computation in a Component-Based OS

In addition to predictability, both reliability and security constraints are increasingly important. Mixed criticality, and open real-time systems execute software of different certification and trust levels. To limit the scope of errant behavior in these systems, a common approach is to raise isolation barriers between software components. However, a thread that executes through multiple components computes on execution stacks spread across each component. As these stacks require backing memory, each component has a finite amount of execution stacks. In this paper, we treat these stacks as shared resources, and investigate the implementation of traditional resource sharing protocols in a real component-based system. We implement multi-resource versions of the Priority Inheritance Protocol (PIP) and Priority Ceiling Protocol (PCP) for these shared stacks and find -- surprisingly -- that neither provide better schedulability characteristics than the other for all system parameterizations. Additionally, we identify the relationship between allocating additional stacks to components, and system schedulability. Given this, we describe and evaluate algorithms to ensure system schedulability while seeking to minimize the amount of memory consumed for stacks.