Results 1  10
of
56
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 ..."
Abstract

Cited by 873 (28 self)
 Add to MetaCart
(Show Context)
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...
A Methodology for Implementing Highly Concurrent Data Objects
, 1993
"... A concurrent object is a data structure shared by concurrent processes. Conventional techniques for implementing concurrent objects typically rely on critical sections: ensuring that only one process at a time can operate on the object. Nevertheless, critical sections are poorly suited for asynchro ..."
Abstract

Cited by 357 (11 self)
 Add to MetaCart
(Show Context)
A concurrent object is a data structure shared by concurrent processes. Conventional techniques for implementing concurrent objects typically rely on critical sections: ensuring that only one process at a time can operate on the object. Nevertheless, critical sections are poorly suited for asynchronous systems: if one process is halted or delayed in a critical section, other, nonfaulty processes will be unable to progress. By contrast, a concurrent object implementation is lock free if it always guarantees that some process will complete an operation in a finite number of steps, and it is wait free if it guarantees that each process will complete an operation in a finite number of steps. This paper proposes a new methodology for constructing lockfree and waitfree implementations of concurrent objects. The object’s representation and operations are written as stylized sequential programs, with no explicit synchronization. Each sequential operation is automatically transformed into a lockfree or waitfree operation using novel synchronization and memory management algorithms. These algorithms are presented for a multiple instruction/multiple data (MIMD) architecture in which n processes communicate by applying atomic read, wrzte, load_linked, and store_conditional operations to a shared memory.
Separating agreement from execution for byzantine fault tolerant services
 IN PROC. SOSP
, 2003
"... We describe a new architecture for Byzantine fault tolerant state machine replication that separates agreement that orders requests from execution that processes requests. This separation yields two fundamental and practically significant advantages over previous architectures. First, it reduces rep ..."
Abstract

Cited by 161 (20 self)
 Add to MetaCart
(Show Context)
We describe a new architecture for Byzantine fault tolerant state machine replication that separates agreement that orders requests from execution that processes requests. This separation yields two fundamental and practically significant advantages over previous architectures. First, it reduces replication costs because the new architecture can tolerate faults in up to half of the state machine replicas that execute requests. Previous systems can tolerate faults in at most a third of the combined agreement/state machine replicas. Second, separating agreement from execution allows a general privacy firewall architecture to protect confidentiality through replication. In contrast, replication in previous systems hurts confidentiality because exploiting the weakest replica can be su#cient to compromise the system. We have constructed a prototype and evaluated it running both microbenchmarks and an NFS server. Overall, we find that the architecture adds modest latencies to unreplicated systems and that its performance is competitive with existing Byzantine fault tolerant systems.
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 ..."
Abstract

Cited by 157 (12 self)
 Add to MetaCart
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 ...
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 ..."
Abstract

Cited by 136 (32 self)
 Add to MetaCart
(Show Context)
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 asynchronous computability theorem for tresilient tasks
 In Proceedings of the 1993 ACM Symposium on Theory of Computing
, 1993
"... We give necessary and sufficient combinatorial conditions characterizing the computational tasks that can be solved by N asynchronous processes, up to t of which can fail by halting. The range of possible input and output values for an asynchronous task can be associated with a highdimensional geom ..."
Abstract

Cited by 103 (15 self)
 Add to MetaCart
(Show Context)
We give necessary and sufficient combinatorial conditions characterizing the computational tasks that can be solved by N asynchronous processes, up to t of which can fail by halting. The range of possible input and output values for an asynchronous task can be associated with a highdimensional geometric structure called a simplicial complex. Our main theorem characterizes computability y in terms of the topological properties of this complex. Most notably, a given task is computable only if it can be associated with a complex that is simply connected with trivial homology groups. In other words, the complex has “no holes!” Applications of this characterization include the first impossibility results for several longstanding open problems in distributed computing, such as the “renaming ” problem of Attiya et. al., the “kset agreement ” problem of Chaudhuri, and a generalization of the approximate agreement problem. 1
Impossibility and universality results for waitfree synchronization
, 1987
"... Impossibility and universality results for waitfree synchronization ..."
Abstract

Cited by 92 (10 self)
 Add to MetaCart
(Show Context)
Impossibility and universality results for waitfree synchronization
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 ..."
Abstract

Cited by 64 (1 self)
 Add to MetaCart
(Show Context)
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...
WaitFree Data Structures in the Asynchronous PRAM Model
 In Proceedings of the 2nd Annual Symposium on Parallel Algorithms and Architectures
, 2000
"... In the asynchronous PRAM model, processes communicate by atomically reading and writing shared memory locations. This paper investigates the extent to which asynchronous PRAM permits longlived, highly concurrent data structures. An implementation of a concurrent object is waitfree if every operati ..."
Abstract

Cited by 62 (13 self)
 Add to MetaCart
(Show Context)
In the asynchronous PRAM model, processes communicate by atomically reading and writing shared memory locations. This paper investigates the extent to which asynchronous PRAM permits longlived, highly concurrent data structures. An implementation of a concurrent object is waitfree if every operation will complete in a finite number of steps, and it is kbounded waitfree, for some k > 0, if every operation will complete within k steps. In the first part of this paper, we show that there are objects with waitfree implementations but no kbounded waitfree implementations for any k, and that there is an infinite hierarchy of objects with implementations that are kbounded waitfree but not Kbounded waitfree for some K > k. In the second part of the paper, we give an algebraic characterization of a large class of objects that do have waitfree implementations in asynchronous PRAM, as well as a general algorithm for implementing them. Our tools include simple iterative algorithms for waitfree approximate agreement and atomic snapshot.
Model Checking for Probability and Time: From Theory to Practice
 In Proc. Logic in Computer Science
, 2003
"... Probability features increasingly often in software and hardware systems: it is used in distributed coordination and routing problems, to model faulttolerance and performance, and to provide adaptive resource management strategies. Probabilistic model checking is an automatic procedure for establi ..."
Abstract

Cited by 61 (1 self)
 Add to MetaCart
(Show Context)
Probability features increasingly often in software and hardware systems: it is used in distributed coordination and routing problems, to model faulttolerance and performance, and to provide adaptive resource management strategies. Probabilistic model checking is an automatic procedure for establishing if a desired property holds in a probabilistic model, aimed at verifying probabilistic specifications such as "leader election is eventually resolved with probability 1", "the chance of shutdown occurring is at most 0.01%", and "the probability that a message will be delivered within 30ms is at least 0.75". A probabilistic model checker calculates the probability of a given temporal logic property being satisfied, as opposed to validity. In contrast to conventional model checkers, which rely on reachability analysis of the underlying transition system graph, probabilistic model checking additionally involves numerical solutions of linear equations and linear programming problems. This paper reports our experience with implementing PRISM (www.cs.bham.ac.uk/dxp/ prism/), a Probabilistic Symbolic Model Checker, demonstrates its usefulness in analysing realworld probabilistic protocols, and outlines future challenges for this research direction.