Implementing Sequentially Consistent Shared Objects using Broadcast and Point-To-Point Communication

• Main Authors: Alan Fekete, M. Frans Kaashoek, Nancy Lynch
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Orca
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.212.9654; http://theory.lcs.mit.edu/tds/papers/Fekete/TM-518.pdf

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 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.