12,572 research outputs found
Brief Announcement: Fast and Scalable Group Mutual Exclusion
The group mutual exclusion (GME) problem is a generalization of the classical mutual exclusion problem in which every critical section is associated with a type or session. Critical sections belonging to the same session can execute concurrently, whereas critical sections belonging to different sessions must be executed serially. The well-known read-write mutual exclusion problem is a special case of the group mutual exclusion problem.
In a shared memory system, locks based on traditional mutual exclusion or its variants are commonly used to manage contention among processes. In concurrent algorithms based on fine-grained synchronization, a single lock is used to protect access to a small number of shared objects (e.g., a lock for every tree node) so as to minimize contention window. Evidently, a large number of shared objects in the system would translate into a large number of locks. Also, when fine-grained synchronization is used, most lock accesses are expected to be uncontended in practice.
Most existing algorithms for the solving the GME problem have high space-complexity per lock. Further, all algorithms except for one have high step-complexity in the uncontented case. This makes them unsuitable for use in concurrent algorithms based on fine-grained synchronization. In this work, we present a novel GME algorithm for an asynchronous shared-memory system that has O(1) space-complexity per GME lock when the system contains a large number of GME locks as well as O(1) step-complexity when the system contains no conflicting requests
Mutual Exclusion in Asynchronous Systems with Failure Detectors
This paper defines the fault-tolerant mutual exclusion problem in a message-passing asynchronous system and determines the weakest failure detector to solve the problem. This failure detector, which we call the trusting failure detector, and which we denote by T, is strictly weaker than the perfect failure detector P but strictly stronger than the eventually perfect failure detector P. The paper shows that a majority of correct processes is necessary to solve the problem with T. Moreover, T is also the weakest failure detector to solve the fault-tolerant group mutual exclusion problem
Automated Synthesis of Distributed Self-Stabilizing Protocols
In this paper, we introduce an SMT-based method that automatically
synthesizes a distributed self-stabilizing protocol from a given high-level
specification and network topology. Unlike existing approaches, where synthesis
algorithms require the explicit description of the set of legitimate states,
our technique only needs the temporal behavior of the protocol. We extend our
approach to synthesize ideal-stabilizing protocols, where every state is
legitimate. We also extend our technique to synthesize monotonic-stabilizing
protocols, where during recovery, each process can execute an most once one
action. Our proposed methods are fully implemented and we report successful
synthesis of well-known protocols such as Dijkstra's token ring, a
self-stabilizing version of Raymond's mutual exclusion algorithm,
ideal-stabilizing leader election and local mutual exclusion, as well as
monotonic-stabilizing maximal independent set and distributed Grundy coloring
On Secure Workflow Decentralisation on the Internet
Decentralised workflow management systems are a new research area, where most
work to-date has focused on the system's overall architecture. As little
attention has been given to the security aspects in such systems, we follow a
security driven approach, and consider, from the perspective of available
security building blocks, how security can be implemented and what new
opportunities are presented when empowering the decentralised environment with
modern distributed security protocols. Our research is motivated by a more
general question of how to combine the positive enablers that email exchange
enjoys, with the general benefits of workflow systems, and more specifically
with the benefits that can be introduced in a decentralised environment. This
aims to equip email users with a set of tools to manage the semantics of a
message exchange, contents, participants and their roles in the exchange in an
environment that provides inherent assurances of security and privacy. This
work is based on a survey of contemporary distributed security protocols, and
considers how these protocols could be used in implementing a distributed
workflow management system with decentralised control . We review a set of
these protocols, focusing on the required message sequences in reviewing the
protocols, and discuss how these security protocols provide the foundations for
implementing core control-flow, data, and resource patterns in a distributed
workflow environment
Self-Stabilizing Wavelets and r-Hops Coordination
We introduce a simple tool called the wavelet (or, r-wavelet) scheme.
Wavelets deals with coordination among processes which are at most r hops away
of each other. We present a selfstabilizing solution for this scheme. Our
solution requires no underlying structure and works in arbritrary anonymous
networks, i.e., no process identifier is required. Moreover, our solution works
under any (even unfair) daemon. Next, we use the wavelet scheme to design
self-stabilizing layer clocks. We show that they provide an efficient device in
the design of local coordination problems at distance r, i.e., r-barrier
synchronization and r-local resource allocation (LRA) such as r-local mutual
exclusion (LME), r-group mutual exclusion (GME), and r-Reader/Writers. Some
solutions to the r-LRA problem (e.g., r-LME) also provide transformers to
transform algorithms written assuming any r-central daemon into algorithms
working with any distributed daemon
The Raincore Distributed Session Service for Networking Elements
Motivated by the explosive growth of the Internet, we study efficient and fault-tolerant distributed session layer
protocols for networking elements. These protocols are
designed to enable a network cluster to share the state
information necessary for balancing network traffic and
computation load among a group of networking elements.
In addition, in the presence of failures, they allow
network traffic to fail-over from failed networking
elements to healthy ones. To maximize the overall
network throughput of the networking cluster, we assume a unicast communication medium for these protocols. The Raincore Distributed Session Service is based on a fault-tolerant token protocol, and provides group membership, reliable multicast and mutual exclusion services in a networking environment. We show that this service provides atomic reliable multicast with consistent ordering. We also show that Raincore token protocol consumes less overhead than a broadcast-based protocol in this environment in terms of CPU task-switching. The Raincore technology was transferred to Rainfinity, a startup company that is focusing on software for Internet reliability and performance. Rainwall, Rainfinityâs first product, was developed using the Raincore Distributed Session Service. We present initial performance results of the Rainwall product that validates our design assumptions and goals
Separation of Circulating Tokens
Self-stabilizing distributed control is often modeled by token abstractions.
A system with a single token may implement mutual exclusion; a system with
multiple tokens may ensure that immediate neighbors do not simultaneously enjoy
a privilege. For a cyber-physical system, tokens may represent physical objects
whose movement is controlled. The problem studied in this paper is to ensure
that a synchronous system with m circulating tokens has at least d distance
between tokens. This problem is first considered in a ring where d is given
whilst m and the ring size n are unknown. The protocol solving this problem can
be uniform, with all processes running the same program, or it can be
non-uniform, with some processes acting only as token relays. The protocol for
this first problem is simple, and can be expressed with Petri net formalism. A
second problem is to maximize d when m is given, and n is unknown. For the
second problem, the paper presents a non-uniform protocol with a single
corrective process.Comment: 22 pages, 7 figures, epsf and pstricks in LaTe
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