An Almost Tight RMR Lower Bound for Abortable Test-And-Set

We prove a lower bound of Omega(log n/log log n) for the remote memory reference (RMR) complexity of abortable test-and-set (leader election) in the cache-coherent (CC) and the distributed shared memory (DSM) model. This separates the complexities of abortable and non-abortable test-and-set, as the latter has constant RMR complexity [Wojciech Golab et al., 2010]. Golab, Hendler, Hadzilacos and Woelfel [Wojciech M. Golab et al., 2012] showed that compare-and-swap can be implemented from registers and test-and-set objects with constant RMR complexity. We observe that a small modification to that implementation is abortable, provided that the used test-and-set objects are atomic (or abortable). As a consequence, using existing efficient randomized wait-free implementations of test-and-set [George Giakkoupis and Philipp Woelfel, 2012], we obtain randomized abortable compare-and-swap objects with almost constant (O(log^* n)) RMR complexity

A Look at Basics of Distributed Computing *

International audienceThis paper presents concepts and basics of distributed computing which are important (at least from the author's point of view), and should be known and mastered by Master students and engineers. Those include: (a) a characterization of distributed computing (which is too much often confused with parallel computing); (b) the notion of a synchronous system and its associated notions of a local algorithm and message adversaries; (c) the notion of an asynchronous shared memory system and its associated notions of universality and progress conditions; and (d) the notion of an asynchronous message-passing system with its associated broadcast and agreement abstractions, its impossibility results, and approaches to circumvent them. Hence, the paper can be seen as a guided tour to key elements that constitute basics of distributed computing

The Fence Complexity of Persistent Sets

This thesis studies fence complexity of concurrent sets in a non-volatile shared memory model. I consider the case where CPU registers and cache memory remain volatile while main memory is non-volatile. Flush instructions are required to force shared state to be written back to non-volatile memory. These flush instructions must be accompanied by the use of expensive fence instructions to enforce ordering among such flushes. Collectively I refer to a flush and a fence as a psync. In this model the system can crash at any time. When the system crashes the contents of volatile memory are lost. I consider lock-free implementations of the set abstract data type and the safety properties of strict linearizability and durable linearizability. Strict linearizability forces crashed operations to take effect before the crash or not take effect at all; the weaker property of durable linearizability enforces this requirement only for operations that have completed prior to the crash event. In this thesis, I consider classes of strict linearizable implementations that guarantee operations take effect at or before the point when the operation is persisted. I prove two lower bounds for lock-free implementations of the set abstract data type. First, I prove that it is impossible to implement strict linearizable lock-free sets in which read-only (or search) operations do not flush or fence. Second, I prove that for any durable-linearizable lock-free set there must exist an execution in which some process must perform at least one redundant psync as part of an update operation. I also present several implementations of persistent concurrent lock-free sets. I evaluate these implementations against existing persistent sets. This evaluation exposes the impact of algorithmic design and safety properties on psync complexity in practice as well as the cost of recovering the data structure following a system crash

Notes on Theory of Distributed Systems

Notes for the Yale course CPSC 465/565 Theory of Distributed Systems