109 research outputs found
Efficient almost wait-free parallel accesible dynamic hashtables
Abstract In multiprogrammed systems, synchronization often turns out to be a performance bottleneck and the source of poor fault-tolerance. Wait-free and lock-free algorithms can do without locking mechanisms, and therefore do not suffer from these problems. We present an efficient almost wait-free algorithm for parallel accessible hashtables, which promises more robust performance and reliability than conventional lock-based implementations. Our solution is as efficient as sequential hashtables. It can easily be implemented using C-like languages and requires on average only constant time for insertion, deletion or accessing of elements. Apart from that, our new algorithm allows the hashtables to grow and shrink dynamically when needed. A true problem of lock-free algorithms is that they are hard to design correctly, even when apparently straightforward. Ensuring the correctness of the design at the earliest possible stage is a major challenge in any responsible system development. Our algorithm contains 81 atomic statements. In view of the complexity of the algorithm and its correctness properties, we turned to the interactive theorem prover PVS for mechanical support. We employ standard deductive verification techniques to prove around 200 invariance properties of our almost wait-free algorithm, and describe how this is achieved using the theorem prover PVS. CR Subject Classification (1991): D.1 Programming techniques AMS Subject Classification (1991): 68Q22 Distributed algorithms, 68P20 Information storage and retrieval Keywords & Phrases: Hashtables, Distributed algorithms, Lock-free, Wait-fre
Boosting Multi-Core Reachability Performance with Shared Hash Tables
This paper focuses on data structures for multi-core reachability, which is a
key component in model checking algorithms and other verification methods. A
cornerstone of an efficient solution is the storage of visited states. In
related work, static partitioning of the state space was combined with
thread-local storage and resulted in reasonable speedups, but left open whether
improvements are possible. In this paper, we present a scaling solution for
shared state storage which is based on a lockless hash table implementation.
The solution is specifically designed for the cache architecture of modern
CPUs. Because model checking algorithms impose loose requirements on the hash
table operations, their design can be streamlined substantially compared to
related work on lockless hash tables. Still, an implementation of the hash
table presented here has dozens of sensitive performance parameters (bucket
size, cache line size, data layout, probing sequence, etc.). We analyzed their
impact and compared the resulting speedups with related tools. Our
implementation outperforms two state-of-the-art multi-core model checkers (SPIN
and DiVinE) by a substantial margin, while placing fewer constraints on the
load balancing and search algorithms.Comment: preliminary repor
Lock-free dynamic hash tables with open addressing
We present an efficient lock-free algorithm for parallel accessible hash tables with open addressing, which promises more robust performance and reliability than conventional lock-based implementations. “Lock-free” means that it is guaranteed that always at least one process completes its operation within a bounded number of steps. For a single processor architecture our solution is as efficient as sequential hash tables. On a multiprocessor architecture this is also the case when all processors have comparable speeds. The algorithm allows processors that have widely different speeds or come to a halt. It can easily be implemented using C-like languages and requires on average only constant time for insertion, deletion or accessing of elements. The algorithm allows the hash tables to grow and shrink when needed.
Lock-free algorithms are hard to design correctly, even when apparently straightforward. Ensuring the correctness of the design at the earliest possible stage is a major challenge in any responsible system development. In view of the complexity of the algorithm, we turned to the interactive theorem prover PVS for mechanical support. We employ standard deductive verification techniques to prove around 200 invariance properties of our algorithm, and describe how this is achieved with the theorem prover PVS.
Concurrent Deterministic Skiplist and Other Data Structures
Skiplists are used in a variety of applications for storing data subject to
order criteria. In this article we discuss the design, analysis and performance
of a concurrent deterministic skip list on many-core NUMA nodes. We also
evaluate the performance of a concurrent lock-free unbounded queue
implementation and three implementations of multi-writer, multi-reader~(MWMR)
hash tables and compare their performance with equivalent implementations from
Intel's Thread Building Blocks~(TBB) library. We focus on strategies for memory
management that reduce page faults and cache misses for the memory access
patterns in these data structures. This paper proposes hierarchical usage of
concurrent data structures in programs to improve memory latencies by reducing
memory accesses from remote NUMA nodes
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