Live Distributed Objects

Distributed multiparty protocols such as multicast, atomic commit, or gossip are currently underutilized, but we envision that they could be used pervasively, and that developers could work with such protocols similarly to how they work with CORBA/COM/.NET/Java objects. We have created a new programming model and a platform in which protocol instances are represented as objects of a new type called live distributed objects: strongly-typed building blocks that can be composed in a type-safe manner through a drag and drop interface. Unlike most prior object-oriented distributed protocol embeddings, our model appears to be flexible enough to accommodate most popular protocols, and to be applied uniformly to any part of a distributed system, to build not only front-end, but also back-end components, such as multicast channels, naming, or membership services. While the platform is not limited to applications based on multicast, it is replication-centric, and reliable multicast protocols are important building blocks that can be used to create a variety of scalable components, from shared documents to fault-tolerant storage or scalable role delegation. We propose a new multicast architecture compatible with the model and designed in accordance with object-oriented principles such as modularity and encapsulation. The architecture represents multicast objects as compositions of smaller objects, glued using a decentralized membership mechanism. The benefits include support for heterogeneous networks by allowing a single multicast protocol instance to simultaneously leverage different mechanisms in different parts of the Internet. Finally, we describe and evaluate a scalable reliable multicast prototype that incorporates a novel approach to scaling with the number of protocol instances by leveraging regular patterns of overlap. The system achieves exceptional performance, scalability, and stability in the presence of perturbations, in part thanks to a novel application of techniques such as priority scheduling or pull-based processing. We describe a previously unnoticed relationship between memory overheads and scheduling and the performance and scalability of a reliable multicast protocol. Our results demonstrate that to build a new global Web operating system that the live objects vision leads to, the distributed protocol and the local system architecture cannot be treated in isolation.This work was supported by DARPA/IPTO under the SRS program, by the Rome Air Force Research Laboratory, AFRL/IF, and by AFOSR (under AF TRUST). Additional support was provided by Intel and NSF