We consider the problem of distinguishing causally-consistent global states in asynchronous distributed systems.Such states are fundamental to asynchronous systems, because they correspond to possible simultaneous global states; their detection arises in a variety of distributed applications, including global checkpointing, deadlock detection, termination detection, and broadcasting.We consider a spectrum of protocol capabilities based on the type of e'nhibition that occurs, i.e. the extent to which the protocol delays events of the underlying system.For the first time we distinguish local versus global inhibition

In this paper we discuss a new knowledgetheoretic definition of agreement appropriate to asynchronous systems.This definition has two important features; first, it uses causality rather than time in its definition and, second, this form of agreement is attainable.In analogy with common knowledge, it is called concurrent common knowledge.Concurrent common knowledge has several applications and we give analyses of two examples that use it.In general, it seems to be the case that applications that involve all processes reaching agreement about some property of a consistent global state are protocols that use concurrent common knowledge.