112 research outputs found
Causal Consistency for Reversible Multiparty Protocols
In programming models with a reversible semantics, computational steps can be
undone. This paper addresses the integration of reversible semantics into
process languages for communication-centric systems equipped with behavioral
types. In prior work, we introduced a monitors-as-memories approach to
seamlessly integrate reversible semantics into a process model in which
concurrency is governed by session types (a class of behavioral types),
covering binary (two-party) protocols with synchronous communication. The
applicability and expressiveness of the binary setting, however, is limited.
Here we extend our approach, and use it to define reversible semantics for an
expressive process model that accounts for multiparty (n-party) protocols,
asynchronous communication, decoupled rollbacks, and abstraction passing. As
main result, we prove that our reversible semantics for multiparty protocols is
causally-consistent. A key technical ingredient in our developments is an
alternative reversible semantics with atomic rollbacks, which is conceptually
simple and is shown to characterize decoupled rollbacks.Comment: Extended, revised version of a PPDP'17 paper
(https://doi.org/10.1145/3131851.3131864
Processes, Systems \& Tests: Defining Contextual Equivalences
In this position paper, we would like to offer and defend a new template to
study equivalences between programs -- in the particular framework of process
algebras for concurrent computation.We believe that our layered model of
development will clarify the distinction that is too often left implicit
between the tasks and duties of the programmer and of the tester. It will also
enlighten pre-existing issues that have been running across process algebras as
diverse as the calculus of communicating systems, the -calculus -- also
in its distributed version -- or mobile ambients.Our distinction starts by
subdividing the notion of process itself in three conceptually separated
entities, that we call \emph{Processes}, \emph{Systems} and \emph{Tests}.While
the role of what can be observed and the subtleties in the definitions of
congruences have been intensively studied, the fact that \emph{not every
process can be tested}, and that \emph{the tester should have access to a
different set of tools than the programmer} is curiously left out, or at least
not often formally discussed.We argue that this blind spot comes from the
under-specification of contexts -- environments in which comparisons takes
place -- that play multiple distinct roles but supposedly always \enquote{stay
the same}.We illustrate our statement with a simple Java example, the
\enquote{usual} concurrent languages, but also back it up with
-calculus and existing implementations of concurrent languages as
well
Causally consistent reversible choreographies: a monitors-as-memories approach
Under a reversible semantics, computation steps can be undone. This paper addresses the integration of reversible semantics into a process model of multiparty protocols (choreographies). Building upon the monitors-as-memories approach that we developed in prior work for reversible binary protocols, we present a reversible process framework for multiparty communication, which improves on prior models by seamlessly integrating asynchrony, decoupled rollbacks, and process passing. As main technical result, we prove that our multiparty, reversible semantics is causally-consistent
Event structures for the reversible early internal pi-calculus
The pi-calculus is a widely used process calculus, which models com-munications between processes and allows the passing of communication links.Various operational semantics of the pi-calculus have been proposed, which canbe classified according to whether transitions are unlabelled (so-called reductions)or labelled. With labelled transitions, we can distinguish early and late semantics.The early version allows a process to receive names it already knows from the en-vironment, while the late semantics and reduction semantics do not. All existingreversible versions of the pi-calculus use reduction or late semantics, despite theearly semantics of the (forward-only) pi-calculus being more widely used than thelate. We define piIH, the first reversible early pi-calculus, and give it a denotationalsemantics in terms of reversible bundle event structures. The new calculus is a re-versible form of the internal pi-calculus, which is a subset of the pi-calculus whereevery link sent by an output is private, yielding greater symmetry between inputsand outputs
Noncommutative localization in noncommutative geometry
The aim of these notes is to collect and motivate the basic localization
toolbox for the geometric study of ``spaces'', locally described by
noncommutative rings and their categories of one-sided modules.
We present the basics of Ore localization of rings and modules in much
detail. Common practical techniques are studied as well. We also describe a
counterexample for a folklore test principle. Localization in negatively
filtered rings arising in deformation theory is presented. A new notion of the
differential Ore condition is introduced in the study of localization of
differential calculi.
To aid the geometrical viewpoint, localization is studied with emphasis on
descent formalism, flatness, abelian categories of quasicoherent sheaves and
generalizations, and natural pairs of adjoint functors for sheaf and module
categories. The key motivational theorems from the seminal works of Gabriel on
localization, abelian categories and schemes are quoted without proof, as well
as the related statements of Popescu, Watts, Deligne and Rosenberg.
The Cohn universal localization does not have good flatness properties, but
it is determined by the localization map already at the ring level. Cohn
localization is here related to the quasideterminants of Gelfand and Retakh;
and this may help understanding both subjects.Comment: 93 pages; (including index: use makeindex); introductory survey, but
with few smaller new result
Reversibility in the higher-order π-calculus
The notion of reversible computation is attracting increasing interest because of its applications in diverse fields, in particular the study of programming abstractions for reliable systems. In this paper, we continue the study un-dertaken by Danos and Krivine on reversible CCS by defining a reversible higher-order π-calculus, called rhoπ. We prove that reversibility in our cal-culus is causally consistent and that the causal information used to support reversibility in rhoπ is consistent with the one used in the causal semantics of the π-calculus developed by Boreale and Sangiorgi. Finally, we show that one can faithfully encode rhoπ into a variant of higher-order π, substantially improving on the result we obtained in the conference version of this paper
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