Dynamic real-time scheduling in distributed environments

Real-time applications are becoming increasingly popular in distributed environments. Distributed real-time applications range from hard real-time applications with periodic or aperiodic tasks and inter-task relative timing constraints to soft real-time applications with best effort timing requirements.; In this dissertation, we introduce a complete system model for scheduling and dispatching hard as well as soft real-time tasks with inter-task temporal dependencies in distributed environments. The model extends the dynamic time-based scheduling method to be applicable to a distributed set of real-time tasks. First, the model maps the distributed scheduling problem into an equivalent single-node problem. Then, it applies the parametric cyclic scheduling method to that problem. Finally, it maps the schedulability results back to the distributed task set. The scheduler uses this process to verify the feasibility of the distributed real-time task set and to generate parametric calendars for run-time execution of tasks. At run-time, the model's distributed dispatcher uses the parametric calendars to provide temporally determinate dispatching of hard real-time tasks and best effort performance for soft real-time tasks. The dispatcher is responsible for synchronizing the execution of distributed nodes' calendars and handling the time-based propagation of inter-node events and messages.; The Common Object Request Broker Architecture (CORBA) is an object-oriented middleware commonly used in distributed applications. It is being standardized by the Object Management Group (OMG). The flexibility, reusability, and inter-operability requirements in distributed real-time applications motivate the use of CORBA middleware.; In this dissertation, we present a time-based real-time CORBA model based on the use of the distributed real-time scheduling and dispatching model. The real-time CORBA model guarantees and enforces time-based QoS requirements for distributed applications' objects while preserving CORBA's remote procedure call (RPC) interface among those objects. At run-time, the model provides time-based dispatching of distributed tasks and end-to-end time-constrained execution of service requests.