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116
Unreliable Failure Detectors for Reliable Distributed Systems
 Journal of the ACM
, 1996
"... We introduce the concept of unreliable failure detectors and study how they can be used to solve Consensus in asynchronous systems with crash failures. We characterise unreliable failure detectors in terms of two properties — completeness and accuracy. We show that Consensus can be solved even with ..."
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Cited by 899 (18 self)
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We introduce the concept of unreliable failure detectors and study how they can be used to solve Consensus in asynchronous systems with crash failures. We characterise unreliable failure detectors in terms of two properties — completeness and accuracy. We show that Consensus can be solved even with unreliable failure detectors that make an infinite number of mistakes, and determine which ones can be used to solve Consensus despite any number of crashes, and which ones require a majority of correct processes. We prove that Consensus and Atomic Broadcast are reducible to each other in asynchronous systems with crash failures; thus the above results also apply to Atomic Broadcast. A companion paper shows that one of the failure detectors introduced here is the weakest failure detector for solving Consensus [Chandra et al. 1992].
WaitFree Synchronization
 ACM Transactions on Programming Languages and Systems
, 1993
"... A waitfree implementation of a concurrent data object is one that guarantees that any process can complete any operation in a finite number of steps, regardless of the execution speeds of the other processes. The problem of constructing a waitfree implementation of one data object from another lie ..."
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Cited by 733 (26 self)
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A waitfree implementation of a concurrent data object is one that guarantees that any process can complete any operation in a finite number of steps, regardless of the execution speeds of the other processes. The problem of constructing a waitfree implementation of one data object from another lies at the heart of much recent work in concurrent algorithms, concurrent data structures, and multiprocessor architectures. In the first part of this paper, we introduce a simple and general technique, based on reduction to a consensus protocol, for proving statements of the form "there is no waitfree implementation of X by Y ." We derive a hierarchy of objects such that no object at one level has a waitfree implementation in terms of objects at lower levels. In particular, we show that atomic read/write registers, which have been the focus of much recent attention, are at the bottom of the hierarchy: they cannot be used to construct waitfree implementations of many simple and familiar da...
Fast Randomized Consensus using Shared Memory
 Journal of Algorithms
, 1988
"... We give a new randomized algorithm for achieving consensus among asynchronous processes that communicate by reading and writing shared registers. The fastest previously known algorithm has exponential expected running time. Our algorithm is polynomial, requiring an expected O(n 4 ) operations ..."
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Cited by 129 (31 self)
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We give a new randomized algorithm for achieving consensus among asynchronous processes that communicate by reading and writing shared registers. The fastest previously known algorithm has exponential expected running time. Our algorithm is polynomial, requiring an expected O(n 4 ) operations. Applications of this algorithm include the elimination of critical sections from concurrent data structures and the construction of asymptotically unbiased shared coins.
The Topological Structure of Asynchronous Computability
 JOURNAL OF THE ACM
, 1996
"... We give necessary and sufficient combinatorial conditions characterizing the tasks that can be solved by asynchronous processes, of which all but one can fail, that communicate by reading and writing a shared memory. We introduce a new formalism for tasks, based on notions from classical algebra ..."
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Cited by 114 (11 self)
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We give necessary and sufficient combinatorial conditions characterizing the tasks that can be solved by asynchronous processes, of which all but one can fail, that communicate by reading and writing a shared memory. We introduce a new formalism for tasks, based on notions from classical algebraic and combinatorial topology, in which a task's possible input and output values are each associated with highdimensional geometric structures called simplicial complexes. We characterize computability in terms of the topological properties of these complexes. This characterization has a surprising geometric interpretation: a task is solvable if and only if the complex representing the task's allowable inputs can be mapped to the complex representing the task's allowable outputs by a function satisfying certain simple regularity properties. Our formalism thus replaces the "operational" notion of a waitfree decision task, expressed in terms of interleaved computations unfolding ...
Composite Registers
 Distributed Computing
, 1993
"... We introduce a shared data object, called a composite register, that generalizes the notion of an atomic register. A composite register is an arraylike shared data object that is partitioned into a number of components. An operation of a composite register either writes a value to a single componen ..."
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Cited by 108 (7 self)
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We introduce a shared data object, called a composite register, that generalizes the notion of an atomic register. A composite register is an arraylike shared data object that is partitioned into a number of components. An operation of a composite register either writes a value to a single component or reads the values of all components. A composite register reduces to an ordinary atomic register when there is only one component. In this paper, we show that multireader, singlewriter atomic registers can be used to implement a composite register in which there is only one writer per component. In a related paper, we show how to use the composite register construction of this paper to implement a composite register with multiple writers per component. These two constructions show that it is possible to implement a shared memory that can be read in its entirety in a single snapshot operation, without using mutual exclusion. Keywords: atomicity, atomic register, composite register, conc...
More Choices Allow More Faults: Set Consensus Problems In Totally Asynchronous Systems
 Information and Computation
, 1992
"... We define the kset consensus problem as an extension of the consensus problem, where each processor decides on a single value such that the set of decided values in any run is of size at most k. We require the agreement condition that all values decided upon are initial values of some processor. ..."
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Cited by 99 (3 self)
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We define the kset consensus problem as an extension of the consensus problem, where each processor decides on a single value such that the set of decided values in any run is of size at most k. We require the agreement condition that all values decided upon are initial values of some processor. We show that the problem has a simple (k  1)resilient protocol in a totally asynchronous system. In an attempt to come up with a matching lower bound on the number of failures, we study the uncertainty condition, which requires that there must be some initial configuration from which all possible input values can be decided. We prove using a combinatorial argument that any kresilient protocol for the kset agreement problem would satisfy the uncertainty condition, while this is not true for any (k  1)resilient protocol.
Contention in Shared Memory Algorithms
, 1993
"... Most complexitymeasures for concurrent algorithms for asynchronous sharedmemory architectures focus on process steps and memory consumption. In practice, however, performance of multiprocessor algorithms is heavily influenced by contention, the extent to which processes access the same location at t ..."
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Cited by 63 (1 self)
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Most complexitymeasures for concurrent algorithms for asynchronous sharedmemory architectures focus on process steps and memory consumption. In practice, however, performance of multiprocessor algorithms is heavily influenced by contention, the extent to which processes access the same location at the same time. Nevertheless, even though contention is one of the principal considerations affecting the performance of real algorithms on real multiprocessors, there are no formal tools for analyzing the contention of asynchronous sharedmemory algorithms. This paper introduces the first formal complexity model for contention in multiprocessors. We focus on the standard multiprocessor architecture in which n asynchronous processes communicate by applying read, write, and readmodifywrite operations to a shared memory. We use our model to derive two kinds of results: (1) lower bounds on contention for well known basic problems such as agreement and mutual exclusion, and (2) tradeoffs betwe...
Time and SpaceEfficient Randomized Consensus
 Journal of Algorithms
, 1992
"... A protocol is presented which solves the randomized consensus problem[9] for shared memory. The protocol uses a total of O(p 2 +n) worstcase expected increment, decrement and read operations on a set of three shared O(logn)bit counters, where p is the number of active processors and n is the ..."
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Cited by 46 (12 self)
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A protocol is presented which solves the randomized consensus problem[9] for shared memory. The protocol uses a total of O(p 2 +n) worstcase expected increment, decrement and read operations on a set of three shared O(logn)bit counters, where p is the number of active processors and n is the total number of processors. It requires less space than previous polynomialtime consensus protocols[6, 7], and is faster when not all of the processors participate in the protocol. A modified version of the protocol yields a weak shared coin whose bias is guaranteed to be in the range 1=2 \Sigma ffl regardless of scheduler behavior, and which is the first such protocol for the sharedmemory model to guarantee that all processors agree on the outcome of the coin. 1 1.
Using Failure Detectors to Solve Consensus in Asynchronous SharedMemory Systems (Extended Abstract)
 In Proceedings of the 8th International Workshop on Distributed Algorithms (WDAG
, 1994
"... Chandra and Toueg proposed a new approach to overcome the impossibility of reaching consensus in asynchronous messagepassing systems subject to crash failures [6]. They augment the asynchronous messagepassing system with a (possibly unreliable) failure detector. Informally, a failure detector prov ..."
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Cited by 44 (1 self)
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Chandra and Toueg proposed a new approach to overcome the impossibility of reaching consensus in asynchronous messagepassing systems subject to crash failures [6]. They augment the asynchronous messagepassing system with a (possibly unreliable) failure detector. Informally, a failure detector provides some information about the processes that have crashed during an execution of the system. In this paper, we present several Consensus algorithms using different types failure detectors in asynchronous sharedmemory systems. We also prove several lower bounds and impossibility results regarding solving Consensus using failure detectors in asynchronous sharedmemory systems.