The Iterated Restricted Immediate Snapshot Model

In the Iterated Immediate Snapshotmodel (${\mathit{IIS}}$) the memory consists of a sequence of one-shot Immediate Snapshot($\mathit{IS}$) objects. Processes access the sequence of $\mathit{IS}$ objects, one-by-one, asynchronously, in a wait-freemanner; any number of processes can crash. Its interest lies in the elegant recursive structure of its runs, hence of the ease to analyze it round by round. In a very interesting way, Borowsky and Gafni have shown that the ${\mathit{IIS}}$ model and the read/write model are equivalent for the wait-free solvability of decision tasks. This paper extends the benefits of the $\mathit{IIS}$ model to partially synchronous systems. Given a shared memory model enriched with a failure detector, what is an equivalent $\mathit{IIS}$ model? The paper shows that an elegant way of capturing the power of a failure detector and other partially synchronous systems in the ${\mathit{IIS}}$ model is by restricting appropriately its set of runs, giving rise to the Iterated Restricted Immediate Snapshotmodel ($\mathit{IRIS}$).

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