This paper studies the relation between agreement and strongly linearizable implementations of various objects. This leads to new results about implementations of concurrent objects from various primitives including window registers, interfering primitives and stacks. We identify that lock-free, respectively, wait-free, strongly linearizable implementations of several concurrent objects entail a form of agreement that does not require full consensus but cannot be implemented in a strongly-linearizable manner with combinations of non-universal primitives. In both cases, lock-free and wait-free, this form of agreement requires a distinguished process to referee a competition that involves all other processes. Our results show that consistent refereeing of such competitions (i.e., once resolved, the outcome cannot be revised in any extension of the execution) requires high coordination power. More specifically, two contest objects are defined and used to help characterize coordination constraints imposed by strong linearizability in lock-free and wait-free implementations, respectively. Both objects are strictly weaker than consensus, in the sense that they have a wait-free linearizable (in fact, decisively linearizable) implementation from reads and writes. The contest objects capture strong linearizability in two complementary ways. First, they admit strongly linearizable implementations from several high-level objects such as queues, snapshots, and counters, so impossibility results for the contest objects immediately carry over to these objects. Second, they admit powerful impossibility results for strong linearizability that involve window registers, interfering primitives and stacks, which are non-universal.

翻译：本文研究了各种对象的共识性与强线性化实现之间的关系。这引出了关于使用窗口寄存器、干扰原语及栈等多种原语实现并发对象的新结论。我们发现，若干并发对象的无锁（lock-free）与无等待（wait-free）强线性化实现隐含了一种不需要完全共识（full consensus）的共识形式，但该形式无法通过非通用原语的组合以强线性化方式实现。在无锁和无等待两种情形下，这种共识形式要求一个区分进程（distinguished process）作为裁判，来仲裁涉及所有其他进程的竞争。我们的结果表明，对此类竞争进行一致裁判（即一旦裁决结果产生，便不能在任意执行扩展中被修改）需要极高的协调能力。更具体地，我们定义并使用了两种竞赛对象（contest objects），分别用于刻画强线性化在无锁实现与无等待实现中施加的协调约束。这两种对象在共识强度上严格弱于共识（consensus），其含义是它们均可通过读写操作实现无等待线性化（更确切地说，是决定性线性化）实现。竞赛对象从两个互补角度捕捉了强线性化的特性。其一，它们允许通过队列、快照、计数器等高层次对象实现强线性化，因此关于竞赛对象的不可能性结论可直接迁移至这些对象。其二，它们为强线性化导出了涉及窗口寄存器、干扰原语及栈（均为非通用原语）的强不可能性结果。