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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 860 (27 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...
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 ..."
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Cited by 350 (11 self)
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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 objectâ€™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.
Atomic Snapshots of Shared Memory
, 1993
"... . This paper introduces a general formulation of atomic snapshot memory, a shared memory partitioned into words written (updated) by individual processes, or instantaneously read (scanned) in its entirety. This paper presents three waitfree implementations of atomic snapshot memory. The first imple ..."
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Cited by 186 (51 self)
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. This paper introduces a general formulation of atomic snapshot memory, a shared memory partitioned into words written (updated) by individual processes, or instantaneously read (scanned) in its entirety. This paper presents three waitfree implementations of atomic snapshot memory. The first implementation in this paper uses unbounded (integer) fields in these registers, and is particularly easy to understand. The second implementation uses bounded registers. Its correctness proof follows the ideas of the unbounded implementation. Both constructions implement a singlewriter snapshot memory, in which each word may be updated by only one process, from singlewriter, nreader registers. The third algorithm implements a multiwriter snapshot memory from atomic nwriter, nreader registers, again echoing key ideas from the earlier constructions. All operations require \Theta(n 2 ) reads and writes to the component shared registers in the worst case. Categories and Subject Discriptors:...
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 133 (32 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.
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 112 (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...
Constructing TwoWriter Atomic Registers
, 1987
"... In this paper, we construct a 2writer, nreader atomic memory register from two lwriter, (n + l)reader atomic memory registers. There are no restrictions on the size of the constructed register. The simulation requires only a single extra bit per real register, and can survive the failure of any ..."
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Cited by 74 (0 self)
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In this paper, we construct a 2writer, nreader atomic memory register from two lwriter, (n + l)reader atomic memory registers. There are no restrictions on the size of the constructed register. The simulation requires only a single extra bit per real register, and can survive the failure of any set of readers and writers. This construction is a part of a systematic investigation of register simulations, by several researchers.
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 ..."
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Cited by 61 (13 self)
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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.
Are WaitFree Algorithms Fast?
, 1991
"... The time complexity of waitfree algorithms in "normal" executions, where no failures occur and processes operate at approximately the same speed, is considered. A lower bound of log n on the time complexity of any waitfree algorithm that achieves approximate agreement among n processes i ..."
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Cited by 39 (11 self)
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The time complexity of waitfree algorithms in "normal" executions, where no failures occur and processes operate at approximately the same speed, is considered. A lower bound of log n on the time complexity of any waitfree algorithm that achieves approximate agreement among n processes is proved. In contrast, there exists a nonwaitfree algorithm that solves this problem in constant time. This implies an (log n) time separation between the waitfree and nonwaitfree computation models. On the positive side, we present an O(log n) time waitfree approximate agreement algorithm; the complexity of this algorithm is within a small constant of the lower bound.
Concurrent Timestamping Made Simple
 Proceedings of Israel Symposium on Theory of Computing and Systems
, 1995
"... Concurrent Timestamp Systems (ctss) allow processes to temporally order concurrent events in an asynchronous shared memory system, a powerful tool for concurrency control, serving as the basis for solutions to coordination problems such as mutual exclusion, `exclusion, randomized consensus, and m ..."
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Cited by 26 (1 self)
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Concurrent Timestamp Systems (ctss) allow processes to temporally order concurrent events in an asynchronous shared memory system, a powerful tool for concurrency control, serving as the basis for solutions to coordination problems such as mutual exclusion, `exclusion, randomized consensus, and multiwriter multireader atomic registers. Solutions to these problems all use an "unbounded number" based concurrent timestamp system (uctss), a construction which is as simple to use as it is to understand. A bounded "blackbox" replacement of uctss would imply equally simple bounded solutions to most of these extensively researched problems. Unfortunately, while all know applications use uctss, all existing solution algorithms are only proven to implement the DolevShavit ctss axioms, which have been widely criticized as "hardtouse." While it is easy to show that a uctss implements the ctss axioms, there is no proof that a system meeting the ctss axioms implements uctss. Thus, the pro...
Optimal MultiWriter MultiReader Atomic Register
 In Proceedings of the 11th ACM Symposium on Principles of Distributed Computing
, 1992
"... . This paper addresses the wide gap in space complexity of atomic, multiwriter, multireader register implementations. While the space complexity of all previous implementations is linear, the lower bounds are logarithmic. We present two implementations which close this gap: The first implementation ..."
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Cited by 22 (0 self)
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. This paper addresses the wide gap in space complexity of atomic, multiwriter, multireader register implementations. While the space complexity of all previous implementations is linear, the lower bounds are logarithmic. We present two implementations which close this gap: The first implementation uses multireader physical registers while the second uses singlereader physical registers. Both implementations are optimal with respect to the two most important complexity criteria: Their space complexity is logarithmic and their time complexity is linear. 1991 Mathematics Subject Classification: 68M10, 68Q22, 68Q25. CR Categories: B.3.2, B.4.3, D.4.1, D.4.4. Keywords and Phrases: Shared Register, Concurrent Reading and Writind, Atomicity, Multiwriter Register. Note: This work is partially supported by NWO through NFI Project ALADDIN under Contract number NF 62376. A preliminary version of this paper was presented in the 11th Annual ACM Symposium on Principles of Distributed Computing, August 1992, Vancouver, Canada. 1