Ordering Actions for Visibility

Several research projects are studying architectures for distributed computing that are founded on the notion of atomic actions operating on objects (instances of abstract data types). Such projects as Clouds at Georgia Tech and Archons at Carnegie-Mellon University are evaluating this approach as the foundation for constructing distributed operating systems. Objects are not new to operating systems. They provide substantial benefits in such dimensions as protection and synchronization, as well as their inherent organizational characteristics. This paper is concerned with synchronization to control ordering, a function often associated with objects. Conventional approaches require substantial extension for the action environment. Typically, they are based on (or equivalent to) general semaphores. Semaphores take no account of the visibility requirements of actions however, and consequently they can allow an action to progress beyond the point at which its effects can be undone. Also, they do not account for failures.