Fine-Grained Dynamic Adaptation of Distributed Components

Dynamic adaptability of distributed components, nowadays scarcely supported, should become a basic principle of future middleware platforms. While most related work envisage somewhat large software reconfigurations, we explore in this paper fine-grained adaptations which intervene within component boundaries. Our experiments are conducted in the framework of the Comet middleware. Dynamic adaptability is supported in Comet through distributed protocols that can be applied at runtime. These protocols may locally denote intrusive modifications which are abstracted through the notion of role. Functional roles are used to describe all-purpose adaptations. We use hook roles as wrappers around existing functionalities. Finally, filter roles interfere with the communication layer. The expressiveness of these complementary abstractions are illustrated in various examples involving non-trivial system adaptations for distributed debugging and communication flow synchronization. A preliminary but promising quantitative evaluation of our adaptation engine under real-world conditions is proposed. We also discuss the difficult but crucial issue of verifying such dynamic adaptations in terms of type, access and security contracts.