An adaptive scheduling service for real-time CORBA

CORBA is an important standard middleware used in the development of distributed applications. It has also been used with distributed real-time applications, through its extension for real-time systems, RT-CORBA. RT-CORBA includes many mechanisms to reduce the non-determinism associated with ordinary CORBA. These mechanisms can be used to provide guarantees for hard real-time systems if the right support from the operating system and network protocols is available. RT-CORBA mechanisms can also be used to improve the timing behavior of soft real-time applications, when the lower layers are not able to provide guarantees. This paper proposes an adaptive scheduling service in the context of RT-CORBA to support the implementation of distributed soft real-time applications. The proposal is based on the adaptation of task periods, so as to reduce system load while still trying to meet the original deadline of all tasks. This is a best-effort approach that dynamically provides graceful degradation in case of overload. The adaptive service proposed in this paper is validated by a set of experiences based on mechanisms of RT-CORBA and TAO, the ORB implementation used.