Alan Fekete, M. Frans Kaashoek, and Nancy Lynch. Implementing Sequentially Consistent Shared Objects using Broadcast and Point-To-Point Communication. Technical Memo MIT/LCS/TM-518, Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, June 1995. .pdf


Abstract

A distributed algorithm that implements a sequentially consistent collection of shared read/update objects using a combination of broadcast and point-to-point communication is presented and proved correct. This algorithm is a generalization of one used in the Orca shared object system.

The algorithm caches objects in the local memory of processors according to application needs; each read operation accesses a single copy of the object, while each update accesses all copies. Copies of all the objects are kept consistent using a strategy based on sequence numbers for broadcasts.

The algorithm is presented in two layers. The lower layer uses the given broadcast and point-to-point communication services, plus sequence numbers, to provide a new communication service called a {\em context multicast channel}. The higher layer uses a context multicast channel to manage the object replication in a consistent fashion. Both layers and their combination are described and verified formally, using the I/O automaton model for asynchronous concurrent systems.