On the Effect of Protected Entry Servicing Policies on the Response Time of Ada Tasks

Real-time multiprocessor systems are being used extensively in industrial applications. Ada provides ample support for such systems, including a complete tasking model providing time predictability, especially when restricted by the Ravenscar profile. A fundamental element of this tasking model is inter-task communication by means of protected objects. The definition of resource locking policies with bounded priority inversion is a fundamental aspect of protected objects, which has received considerable attention, with some interesting results that can be used in multiprocessor real-time systems. However, there is another important subject, the service policy for protected entries, that has received less attention in the research community and is also important in order to guarantee a predictable time behaviour. The impact of the service model on the response time analysis of multiprocessor real-time systems is evaluated in the paper for the self-service model and the proxy model, and their relation to the MSRP and the MrsP locking policies is discussed. Extensions to response time analysis for the proxy model with both locking policies are also contributed.