Reflections on an Adaptable Real-Time Metalevel Architecture

Existing reflective object-oriented real-time systems typically provide the programmer with a single mechanism or policy. With the advent of a new generation of application software with demand for (soft) real-time behavior, this limited choice may not be sufficient. We propose a metalevel architecture, where an application can choose from different real-time mechanisms and policies, thereby configuring its real-time behavior dynamically at run-time. This allows the adaptation to requirements that are not anticipated during application development. An example from the field of multimedia systems motivates our approach. We achieve this adaptability by structuring our metalevel into separate entities concerned with the support of different areas such as active object models, scheduling, and synchronization. These entities implement a variety of different real-time mechanisms and policies. This metalevel architecture is implemented using standard reflective mechanisms such as metalevel interceptions and metaobject protocols. Some preliminary performance figures give an impression of the price that has to be paid when our approach is used.