Simple Optimal Wait-free Multireader Registers

多字单写者寄存器空间复杂度的上界与下界

Upper and Lower Bounds on the Space Complexity of Multi-word Single-Writer Registers

该研究针对单写者多字寄存器，证明了其空间复杂度的匹配上下界，提出了渐近紧的无等待模拟算法，改进了此前的空间上界，提升了多字寄存器模拟的空间效率。

On implementing SWMR registers from SWSR registers in systems with Byzantine failures

The implementation of registers from (potentially) weaker registers is a classical problem in the theory of distributed computing. Since Lamport's pioneering work [13], this problem has been extensively studied in the context of asynchronous processes with crash failures. In this paper, we investigate this problem in the context of Byzantine process failures, with and without process signatures. We first prove that, without signatures, there is no wait-free linearizable implementation of a 1-writer n-reader register from atomic 1-writer 1-reader registers. In fact, we show a stronger result, n…

A one-bit swap object using test-and-sets and a max register

We describe a linearizable, wait-free implementation of a one-bit swap object from a single max register and an unbounded array of test-and-set bits. Each swap operation takes at most three steps. Using standard randomized constructions, the max register and test-and-set bits can be replaced by read-write registers, at the price of raising the cost of a swap operation to an expected O(max(log n, min(log t, n))) steps, where t is the number of times the swap object has previously changed its value and n is the number of processes.

Revisionist Simulations: A New Approach to Proving Space Lower Bounds

Determining the space complexity of $x$-obstruction-free $k$-set agreement for $x\leq k$ is an open problem. In $x$-obstruction-free protocols, processes are required to return in executions where at most $x$ processes take steps. The best known upper bound on the number of registers needed to solve this problem among $n>k$ processes is $n-k+x$ registers. No general lower bound better than $2$ was known. We prove that any $x$-obstruction-free protocol solving $k$-set agreement among $n>k$ processes uses at least $\lfloor(n-x)/(k+1-x)\rfloor+1$ registers. Our main tool is a simulation that serv…

GPU启发式共享内存模型中的拜占庭线性化单写多读寄存器

Byzantine-linearizable Single-Writer Multi-Reader Register in the GPU-Inspired Shared Memory Model

该研究在GPU启发式共享内存模型中，针对任意线程可能表现拜占庭行为的问题，实现了两种拜占庭线性化SWMR寄存器，利用GPU锁步执行弥补访问控制缺失，为分布式容错寄存器提供了新方案。

Deterministic and Fast Randomized Test-and-Set in Optimal Space

The test-and-set object is a fundamental synchronization primitive for shared memory systems. A test-and-set object stores a bit, initialized to 0, and supports one operation, test&set(), which sets the bit's value to 1 and returns its previous value. This paper studies the number of atomic registers required to implement a test-and-set object in the standard asynchronous shared memory model with n processes. The best lower bound is log(n)-1 for obstruction-free (Giakkoupis and Woelfel, 2012) and deadlock-free (Styer and Peterson, 1989) implementations. Recently a deterministic obstruction-fre…

强线性化不可能性结果：一致裁判的困难

Impossibility Results for Strong Linearizability: The Difficulty of Consistent Refereeing

研究强线性化实现与一致性之间的关系，定义两种竞赛对象，证明强线性化需要高协调能力，且某些对象无法通过非通用原语实现强线性化。

Space Complexity of Implementing Large Shared Registers

We prove two new space lower bounds for the problem of implementing a large shared register using smaller physical shared registers. We focus on the case where both the implemented and physical registers are single-writer, which means they can be accessed concurrently by multiple readers but only by a single writer. To strengthen our lower bounds, we let the physical registers be atomic and we only require the implemented register to be regular. Furthermore, the lower bounds hold for obstruction-free implementations, which means they also hold for lock-free and wait-free implementations. If $m…

Relaxed Queues and Stacks from Read/Write Operations

Considering asynchronous shared memory systems in which any number of processes may crash, this work identifies and formally defines relaxations of queues and stacks that can be non-blocking or wait-free while being implemented using only read/write operations. Set-linearizability and Interval-linearizability are used to specify the relaxations formally, and precisely identify the subset of executions which preserve the original sequential behavior. The relaxations allow for an item to be returned more than once by different operations, but only in case of concurrency; we call such a property …

Reducing Compare-and-Swap to Consensus Number One Primitives

The consensus number of an object is the maximum number of processes among which binary consensus can be solved using any number of instances of the object and read-write registers. Herlihy [6] showed in his seminal work that if an object has a consensus number of n, then there is a universal construction for a wait-free and linearizable implementation of any non-trivial concurrent object or data structure that is shared among n processes. Thus, a synchronization object such as compare-and-swap with an infinite consensus number and the corresponding instruction can be viewed as "strong". On th…

内存匿名且无饥饿的互斥：可能性与不可能性结果

Memory-Anonymous Starvation-Free Mutual Exclusion: Possibility and Impossibility Results

本文研究匿名共享内存系统中的无饥饿互斥问题，针对无记忆算法证明：两进程使用m≥7个匿名寄存器可实现无饥饿互斥当且仅当m为奇数，而三进程及以上则不可能实现，揭示了无故障系统中全局进展与个体进展之间的根本性差异。