64,509 research outputs found
On Modelling and Analysis of Dynamic Reconfiguration of Dependable Real-Time Systems
This paper motivates the need for a formalism for the modelling and analysis
of dynamic reconfiguration of dependable real-time systems. We present
requirements that the formalism must meet, and use these to evaluate well
established formalisms and two process algebras that we have been developing,
namely, Webpi and CCSdp. A simple case study is developed to illustrate the
modelling power of these two formalisms. The paper shows how Webpi and CCSdp
represent a significant step forward in modelling adaptive and dependable
real-time systems.Comment: Presented and published at DEPEND 201
Process Algebras
Process Algebras are mathematically rigorous languages with well defined semantics that permit describing and verifying properties of concurrent communicating systems.
They can be seen as models of processes, regarded as agents that act and interact continuously with other similar agents and with their common environment. The agents may be real-world objects (even people), or they may be artifacts, embodied perhaps in computer hardware or software systems.
Many different approaches (operational, denotational, algebraic) are taken for describing the meaning of processes. However, the operational approach is the reference one. By relying on the so called Structural Operational Semantics (SOS), labelled transition systems are built and composed by using the different operators of the many different process algebras. Behavioral equivalences are used to abstract from unwanted details and identify those systems that react similarly to external
experiments
A unifying Petri net model of non-interference and non-deducibility information flow security
In this paper we introduce FIFO Information Flow Nets (FIFN) as a model for describing information flow security properties. The FIFN is based on Petri nets and has been derived from the work described in [Var89], [Var90] and [Rou86]. Using this new model, we present the information flow security properties Non-Interference between Places (which corresponds to Non-Interference) and Non-Deducibility on Views (which corresponds to Non-Deducibility on Inputs). Then we consider a very general composition operation and show that neither Non-Interference on Places nor Non-Deducibility on Views is preserved under this composition operation. This leads us to a new definition of information flow security referred to as the Feedback Non-Deducibility on Views. We then show that this definition is preserved under the composition operation. This leads us to a new definition of information flow security referred to as the Feedback Non-Deducibility on Views. We then show that this definition is preserved under the composition operation. We then show some similarities between this property and the notion of Non-Deducibility on Strategies
Fifty years of Hoare's Logic
We present a history of Hoare's logic.Comment: 79 pages. To appear in Formal Aspects of Computin
Idle Period Propagation in Message-Passing Applications
Idle periods on different processes of Message Passing applications are
unavoidable. While the origin of idle periods on a single process is well
understood as the effect of system and architectural random delays, yet it is
unclear how these idle periods propagate from one process to another. It is
important to understand idle period propagation in Message Passing applications
as it allows application developers to design communication patterns avoiding
idle period propagation and the consequent performance degradation in their
applications. To understand idle period propagation, we introduce a methodology
to trace idle periods when a process is waiting for data from a remote delayed
process in MPI applications. We apply this technique in an MPI application that
solves the heat equation to study idle period propagation on three different
systems. We confirm that idle periods move between processes in the form of
waves and that there are different stages in idle period propagation. Our
methodology enables us to identify a self-synchronization phenomenon that
occurs on two systems where some processes run slower than the other processes.Comment: 18th International Conference on High Performance Computing and
Communications, IEEE, 201
Non-Coherent Code Acquisition in the Multiple Transmit/Multiple Receive Antenna Aided Single- and Multi-Carrier DS-CDMA Downlink
We analyse the characteristics of the Non-Coherent (NC) Multiple Transmit/Multiple Receive (MTMR) antenna aided Multi-Carrier (MC) DS-CDMA downlink employing a serial search based acquisition scheme, when communicating over spatially uncorrelated Rayleigh channels. The associated Mean Acquisition Time (MAT) performance trends are characterised as a function of both the number of antennas and that of the number of subcarriers. It is shown that the employment of both multiple transmit antennas and multiple subcarriers is typically detrimental in terms of the achievable NC acquisition performance, while that obtained by exploiting multiple receive antennas is always beneficial, regardless whether single-path or multi-path scenarios are considered. Based on our results justified by information theoretic considerations, our acquisition design guidelines are applicable to diverse NC MTMR antenna aided scenarios. Index TermsāMC-DS-CDMA, non-coherent, transmit/receive/ frequency diversity
Session Communication and Integration
The scenario-based specification of a large distributed system is usually
naturally decomposed into various modules. The integration of specification
modules contrasts to the parallel composition of program components, and
includes various ways such as scenario concatenation, choice, and nesting. The
recent development of multiparty session types for process calculi provides
useful techniques to accommodate the protocol modularisation, by encoding
fragments of communication protocols in the usage of private channels for a
class of agents. In this paper, we extend forgoing session type theories by
enhancing the session integration mechanism. More specifically, we propose a
novel synchronous multiparty session type theory, in which sessions are
separated into the communicating and integrating levels. Communicating sessions
record the message-based communications between multiple agents, whilst
integrating sessions describe the integration of communicating ones. A
two-level session type system is developed for pi-calculus with syntactic
primitives for session establishment, and several key properties of the type
system are studied. Applying the theory to system description, we show that a
channel safety property and a session conformance property can be analysed.
Also, to improve the utility of the theory, a process slicing method is used to
help identify the violated sessions in the type checking.Comment: A short version of this paper is submitted for revie
An occam Style Communications System for UNIX Networks
This document describes the design of a communications system which provides occam style communications primitives under a Unix environment, using TCP/IP protocols, and any number of other protocols deemed suitable as underlying transport layers. The system will integrate with a low overhead scheduler/kernel without incurring significant costs to the execution of processes within the run time environment. A survey of relevant occam and occam3 features and related research is followed by a look at the Unix and TCP/IP facilities which determine our working constraints, and a description of the T9000 transputer's Virtual Channel Processor, which was instrumental in our formulation. Drawing from the information presented here, a design for the communications system is subsequently proposed. Finally, a preliminary investigation of methods for lightweight access control to shared resources in an environment which does not provide support for critical sections, semaphores, or busy waiting, is made. This is presented with relevance to mutual exclusion problems which arise within the proposed design. Future directions for the evolution of this project are discussed in conclusion
Propagation and Decay of Injected One-Off Delays on Clusters: A Case Study
Analytic, first-principles performance modeling of distributed-memory
applications is difficult due to a wide spectrum of random disturbances caused
by the application and the system. These disturbances (commonly called "noise")
destroy the assumptions of regularity that one usually employs when
constructing simple analytic models. Despite numerous efforts to quantify,
categorize, and reduce such effects, a comprehensive quantitative understanding
of their performance impact is not available, especially for long delays that
have global consequences for the parallel application. In this work, we
investigate various traces collected from synthetic benchmarks that mimic real
applications on simulated and real message-passing systems in order to pinpoint
the mechanisms behind delay propagation. We analyze the dependence of the
propagation speed of idle waves emanating from injected delays with respect to
the execution and communication properties of the application, study how such
delays decay under increased noise levels, and how they interact with each
other. We also show how fine-grained noise can make a system immune against the
adverse effects of propagating idle waves. Our results contribute to a better
understanding of the collective phenomena that manifest themselves in
distributed-memory parallel applications.Comment: 10 pages, 9 figures; title change
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