Computing particular snapshots in distributed systems

The focus of this work is on a particular class of unstable global states: the states with no in-transit message. A characterization of these states and their interest are given, along with the principles of their detection. As detecting these states requires a network traversal, choosing a particular implementation of this traversal gives one instance from a family of algorithms. The algorithm based on a virtual Hamiltonian cycle (a ring traversal) is presented and proved to be correct. The exposition of the principles and of the ring algorithm is done in an analytic way: algorithmic techniques are given separately (markers, message counting, network traversal) to lay down the snapshot definition properties