Synchronization and recovery of actions

We introduce an approach to robust computation in distributed systems. This approach is the foundation for reliability in the Clouds decentralized operating system. It is based on atomic actions operating on instances of abstract data types (objects). We present an event-based model of computation in which scheduling of responses to operation invocations is controlled by objects. We discuss an integrated strategy for synchronization and recovery which uses relationships between the abstract states of objects to track dependencies between actions. Serializability is defined in terms of the semantics of operations. This permits high concurrency to be obtained in non-serializable implementations without deviation from serializable abstract behavior. We define a class of schedulers that allows objects to make autonomous scheduling decisions. We present the use of non-serializable operation semantics. Finally, we discuss implementation of the model, including action synchronization, object operation ordering using action-based counting semaphores, and action recovery.