Single-Bit Messages Are Insufficient in the Presence of Duplication

Engelhardt, Kai; Moses, Yoram

doi:10.1007/11603771_3

“…Fekete and Lynch proved that reliable end-to-end communication is impossible in FF (and thus in FDF) without messages containing header information [6]. In [5] we show that it is impossible in RDF to reliably transmit more than a single bit by only exchanging one-bit messages between two processes. This implies that a message set consisting of at least three different packets is necessary to transmit sequences of bits reliably in RDF.…”

Section: Example 1 (Value Transmit)mentioning

confidence: 71%

Safe Composition of Distributed Programs Communicating over Order-Preserving Imperfect Channels

Engelhardt

¹

,

Moses

²

2005

Distributed Computing – IWDC 2005

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The fundamental question considered in this paper is when program Q, if executed immediately after program P, is guaranteed not to interfere with P and be safe from interference by P. If a message sent by one of these programs is received by the other, it may affect and modify the other's execution. The notion of communication-closed layers (CCLs) introduced by Elrad and Francez in 1982 is a useful tool for studying such interference. CCLs have been considered mainly in the context of reliable FIFO channels (without duplication), where one can design program layers that do not interfere with any other layer. When channels are less than perfect such programs are no longer feasible. The absence of interference between layers becomes context-dependent. In this paper we study the impact of message duplication and loss on the safety of layer composition. Using a communication phase operator, the fits after relation among programs is defined. If program Q fits after P then P and Q will not interfere with each other in executions of P * Q (P immediately followed by Q). For programs P and Q in a natural class of programs we outline efficient algorithms for the following: (1) deciding whether Q fits after P; (2) deciding whether Q seals P, meaning that Q fits after P and no following program can communicate with P; and (3) constructing a separator S that both fits after P and satisfies that Q fits after P * S .

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“…As we shall see, in REL, the CCL property depends in an essential way on Lamport causality [Lam78]. Indeed, to ensure CCL, causality is all that is needed in REL, whereas either duplication or loss already mandate the need for headers in messages [FL90,EM05c].…”

Section: Introductionmentioning

confidence: 99%

Causing communication closure: safe program composition with reliable non-FIFO channels

Engelhardt

¹

,

Moses

²

2009

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A semantic framework for analyzing safe composition of distributed programs is presented. Its applicability is illustrated by a study of program composition when communication is reliable but not necessarily FIFO. In this model, special care must be taken to ensure that messages do not accidentally overtake one another in the composed program. We show that barriers do not exist in this model. Indeed, no program that sends or receives messages can automatically be composed with arbitrary programs without jeopardizing their intended behavior. Safety of composition becomes context-sensitive and new tools are needed for ensuring it. A notion of sealing is defined, where if a program P is immediately followed by a program Q that seals P then P will be communication-closed-it will execute as if it runs in isolation. The investigation of sealing in this model reveals a novel connection between Lamport causality and safe composition. A characterization of sealable programs is given, as well as efficient algorithms for testing if Q seals P and for constructing a seal for a significant class of programs. It is shown that every sealable program that is open to interference on O(n 2 ) channels can be sealed using O(n) messages.

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“…As we shall see, in REL, the CCL property depends in an essential way on Lamport causality [Lam78]. Indeed, to ensure CCL, causality is all that is needed in REL, whereas either duplication or loss already mandate the need for headers in messages [FL90,EM05c].…”

Section: Introductionmentioning

confidence: 99%

Causing Communication Closure: Safe Program Composition with Non-FIFO Channels

Engelhardt

¹

,

Moses

²

2005

Lecture Notes in Computer Science

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A semantic framework for analyzing safe composition of distributed programs is presented. Its applicability is illustrated by a study of program composition when communication is reliable but not necessarily FIFO. In this model, special care must be taken to ensure that messages do not accidentally overtake one another in the composed program. We show that barriers do not exist in this model. Indeed, no program that sends or receives messages can automatically be composed with arbitrary programs without jeopardizing their intended behavior. Safety of composition becomes context-sensitive and new tools are needed for ensuring it. A notion of sealing is defined, where if a program P is immediately followed by a program Q that seals P then P will be communication-closed-it will execute as if it runs in isolation. The investigation of sealing in this model reveals a novel connection between Lamport causality and safe composition. A characterization of sealable programs is given, as well as efficient algorithms for testing if Q seals P and for constructing a seal for a significant class of programs. It is shown that every sealable program that is open to interference on O(n 2 ) channels can be sealed using O(n) messages.

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Single-Bit Messages Are Insufficient in the Presence of Duplication

Cited by 4 publications

References 6 publications

Safe Composition of Distributed Programs Communicating over Order-Preserving Imperfect Channels

Safe Composition of Distributed Programs Communicating over Order-Preserving Imperfect Channels

Causing communication closure: safe program composition with reliable non-FIFO channels

Causing Communication Closure: Safe Program Composition with Non-FIFO Channels

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