Browse Theses

This thesis aims at the development of a comprehensive set of techniques for synchronizing real-time tasks on uniprocessors, multiprocessors, distributed systems and distributed real-time databases. In particular, we investigate the class of priority inheritance protocols that solve the uncontrolled priority inversion problem. We show that there exist efficient priority inheritance protocols on uniprocessors that exhibit two very desirable properties. First, they minimize the worst-case blocking time of a task to at most the duration of execution of a single critical section. Secondly, these protocols prevent the formation of deadlocks. These properties allow us to derive a set of sufficient conditions under which a set of periodic tasks using one of these protocols is schedulable. The semaphore control protocol is an efficient priority inheritance protocol and is optimal in the sense that it embeds sufficient and necessary conditions to obtain these two properties. This protocol forms the basis of other approximations which can be easily implemented. Experimental studies comparing the relative performances of these protocols and commonly used protocols are carried out by modifying an Ada run-time system.

The priority inversion problem becomes even more acute in the context of multiprocessors and distributed systems. We develop a priority inheritance protocol for multiprocessor systems that solves this problem by bounding the blocking duration of a task waiting for globally shared resources. We also extend the priority inheritance protocols to distinguish between the read and write semantics of locks in real-time databases. We show that compatible locks are not necessarily useful in real-time databases, but our protocol shall exploit such lock compatibility only when it enhances guaranteed performance. This protocol can be extended to decomposable distributed real-time databases as well.

This work is being done as part of the Advanced Real-time Technologies (ART) project at Carnegie Mellon University. (Abstract shortened with permission of author.)