Implementing a semi-active replication strategy in CHORUS/ClassiX, a distributed real-time executive

The paper reports a practical implementation of a strategy to support semi-active replication of real-time software components (i.e. sets of tasks) running on the Chorus/ClassiX distributed operating system. The main property of the replication strategy developed in this paper is to solve the major difficulty of replica determinism. The semi-active replication scheme consists of a leader software component and identical follower replicas. Only the leader component sends out application messages as well as notifications indicating the order the messages have been consumed and produced. Dynamic non-deterministic scheduling of tasks within the different replicas may cause the follower tasks to lag in their execution regarding the leader ones.