Causal memory: definitions, implementation, and programming

Ahamad, Mustaque; Neiger, Gil; Burns, James E.; Kohli, Prince; Hutto, Phillip W.

doi:10.1007/s004460050008

Cited by 37 publications

(47 citation statements)

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“…We then have w T1 (X) < H r T2 (X). Because (1) the linearization point of T1 (line 11) is placed before it writes X (line 14), (2) w T1 (X) < H r T2 (X) and (3) the linearization point of T2 is placed after its read of X (try to commit T2 () is its last operation), the read-from relation is respected, which concludes the lemma. Proof The proof follows directly from the definition of the linearization points (they are placed during the lifetime of the transactions).…”

mentioning

confidence: 79%

“…It states that (1) no transaction (committed or aborted) reads values from an inconsistent global state, (2) the consistent global states read by the committed transactions are mutually consistent (in the sense that they can be totally ordered) but (3) while the global state read by each aborted transaction is consistent from its individual point of view, the global states read by any two aborted transactions are not required to be mutually consistent. Said differently, virtual world consistency requires that (1) all the committed transactions be serializable [20] (so they all have the same "witness sequential execution") or linearizable [14] (if we want this witness execution to also respect real time) and (2) each aborted transaction (reduced to a read prefix as explained previously) reads values that are consistent with respect to its causal past only.…”

Section: Irisamentioning

confidence: 99%

“…Causally consistent transactions The concept of causal consistency for read/write objects has been introduced in [2] under the name causal memory. It has then been extended to transactions in [21] where only the committed transactions are considered.…”

Section: From Virtual World Consistency To Causal Consistencymentioning

confidence: 99%

See 2 more Smart Citations

A Versatile STM Protocol with Invisible Read Operations That Satisfies the Virtual World Consistency Condition

Imbs

Raynal

2010

Structural Information and Communication Complexity

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To cite this version:Damien Imbs, Michel Raynal. A versatile STM protocol with invisible read operations that satisfies the virtual world consistency condition. Abstract:The aim of a Software Transactional Memory (STM) is to discharge the programmers from the management of synchronization in multiprocess programs that access concurrent objects. To that end, a STM system provides the programmer with the concept of a transaction. The job of the programmer is to decompose each sequential process the application is made up of into transactions. A transaction is a piece of code that accesses concurrent objects, but contains no explicit synchronization statement. It is the job of the underlying STM system to provide the illusion that each transaction appears as being executed atomically. For efficiency, a STM system allows transactions to execute concurrently. Consequently, due to the underlying STM concurrency management, a transaction commits or aborts. This paper first presents a new STM consistency condition, called virtual world consistency. This condition states that no transaction reads object values from an inconsistent global state. It is similar to opacity for the committed transactions but weaker for the aborted transactions. More precisely, it states that (1) the committed transactions can be totally ordered, and (2) the values read by each aborted transaction are consistent with respect to its causal past only. Hence, virtual world consistency is weaker than opacity while keeping its spirit. Then, assuming the objects shared by the processes are atomic read/write objects, the paper presents a STM protocol that ensures virtual world consistency (while guaranteeing the invisibility of the read operations). From an operational point of view, this protocol is based on a vector-clock mechanism. Finally, the paper considers the case where the shared objects are regular read/write objects. It also shows how the protocol can be weakened to satisfy the causal consistency condition (that is weaker than virtual world consistency).Virtual world consistency does not require the aborted transactions to agree on what they have seen. This is captured by the local vector clocks associated with each process and the vector timestamps associated with each object. From a comprehensive point of view, the paper addresses how the interplay of these local control informations allows the execution of a set of transactions to be provided with a global meaning. Key-words:Atomic object, Causal past, Commit/abort, Concurrency control, Consistency condition, Consistent global state, Lock, Read-from relation, Regular Read/write object, Serializability, Shared memory, Software transactional memory, Vector clock, Transaction.

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mentioning

confidence: 79%

Section: Irisamentioning

confidence: 99%

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A Versatile STM Protocol with Invisible Read Operations That Satisfies the Virtual World Consistency Condition

Imbs

Raynal

2010

Structural Information and Communication Complexity

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“…The execution of ins(a ≺ e ≺ b) requires a and b, or their tombstones, to be present. The respect of preconditions ensures the causal consistency criteria [3]. All operations are executed on a state where they are legal.…”

Section: Woot Approachmentioning

confidence: 99%

Data consistency for P2P collaborative editing

Oster

Urso

Molli

et al. 2006

Proceedings of the 2006 20th Anniversary Conference on Computer Supported Cooperative Work

155

177

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“…A write of value v into object x by process p i is denoted w i (x)v; similarly a read of x by process p j is denoted r j (x)v where v is the value returned by the read operation; op will denote either r (read) or w (write). To simplify the analyses, as in [3], [20], [26], we assume that all values written into an object x are distinct 3 . Moreover, the parameters of an operation are omitted when they are not important.…”

Section: A Shared Memory Abstractionmentioning

confidence: 99%

A Methodological Construction of an Efficient Sequentially Consistent Distributed Shared Memory

Cholvi

Fernández

Jiménez

et al. 2009

The Computer Journal

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The paper proposes a simple protocol that ensures sequential consistency. The protocol assumes that the shared memory abstraction is supported by the local memories of nodes, that can communicate only by exchanging messages through reliable channels. Unlike other sequential consistency protocols, the one proposed here does not rely on a strong synchronization mechanism, such as an atomic broadcast primitive or a central node managing a copy of every shared object. From a methodological point of view, the protocol is built incrementally starting from the very definition of sequential consistency. It has the noteworthy property that a process that issues a write operation never has to wait for other processes. Depending on the current local state, most read operations issued also have the same property.Keywords: Distributed Systems, Distributed Shared Memory, Sequential Consistency. I. INTRODUCTIONThe definition of a consistency criterion is crucial for the correctness of a multiprocess program [10], [23]. Basically, a consistency criterion defines which value has to be returned when a read operation on a shared object is invoked by a process [11], [14], [18]. The strongest (i.e., most constraining) consistency criterion is atomic consistency [20], also called linearizability [13]. It states that a read returns the value written by the latest preceding write, "latest" referring to real-time occurrence order (concurrent writes being totally ordered). Causal consistency [3], [5] is a weaker criterion, stating that a read does not get an overwritten value. Causal consistency allows concurrent writes; consequently, it is possible that concurrent read operations on the same object get different values. This occurs when those values have been produced by concurrent writes. Other consistency criteria weaker than causal consistency have also been proposed [1], [27]. This paper focuses on sequential consistency [16]. This criterion lies between atomic consistency and causal consistency. Informally, it states that a multiprocess program executes correctly if its results could have been produced by executing that program on a single processor system. This means that an execution is correct if we can totally order its operations in such a way that 1) The order of operations in each process is preserved, and 2) Each read operation obtains the latest previously written value, "latest" referring here to the total order. The difference between atomic consistency and sequential consistency lies in the meaning of the word "latest". This word refers to real-time when we consider atomic consistency, while it refers to a logical time notion when we consider sequential consistency. Namely, the logical time defined by the total order.

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Causal memory: definitions, implementation, and programming

Cited by 37 publications

References 0 publications

A Versatile STM Protocol with Invisible Read Operations That Satisfies the Virtual World Consistency Condition

A Versatile STM Protocol with Invisible Read Operations That Satisfies the Virtual World Consistency Condition

Data consistency for P2P collaborative editing

A Methodological Construction of an Efficient Sequentially Consistent Distributed Shared Memory

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