35,726 research outputs found
Group Mutual Exclusion in Linear Time and Space
We present two algorithms for the Group Mutual Exclusion (GME) Problem that
satisfy the properties of Mutual Exclusion, Starvation Freedom, Bounded Exit,
Concurrent Entry and First Come First Served. Both our algorithms use only
simple read and write instructions, have O(N) Shared Space complexity and O(N)
Remote Memory Reference (RMR) complexity in the Cache Coherency (CC) model. Our
first algorithm is developed by generalizing the well-known Lamport's Bakery
Algorithm for the classical mutual exclusion problem, while preserving its
simplicity and elegance. However, it uses unbounded shared registers. Our
second algorithm uses only bounded registers and is developed by generalizing
Taubenfeld's Black and White Bakery Algorithm to solve the classical mutual
exclusion problem using only bounded shared registers. We show that contrary to
common perception our algorithms are the first to achieve these properties with
these combination of complexities.Comment: A total of 21 pages including 5 figures and 3 appendices. The bounded
shared registers algorithm in the old version has a subtle error (that has no
easy fix) necessitating replacement. A correct, but fundamentally different,
bounded shared registers algorithm, which has the same properties claimed in
the old version is presented in this new version. Also, this version has an
additional autho
Self-stabilizing tree algorithms
Designers of distributed algorithms have to contend with the problem of making the algorithms tolerant to several forms of coordination loss, primarily faulty initialization. The processes in a distributed system do not share a global memory and can only get a partial view of the global state. Transient failures in one part of the system may go unnoticed in other parts and thus cause the system to go into an illegal state. If the system were self-stabilizing, however, it is guaranteed that it will return to a legal state after a finite number of state transitions. This thesis presents and proves self-stabilizing algorithms for calculating tree metrics and for achieving mutual exclusion on a tree structured distributed system
Efficient Symmetry Reduction and the Use of State Symmetries for Symbolic Model Checking
One technique to reduce the state-space explosion problem in temporal logic
model checking is symmetry reduction. The combination of symmetry reduction and
symbolic model checking by using BDDs suffered a long time from the
prohibitively large BDD for the orbit relation. Dynamic symmetry reduction
calculates representatives of equivalence classes of states dynamically and
thus avoids the construction of the orbit relation. In this paper, we present a
new efficient model checking algorithm based on dynamic symmetry reduction. Our
experiments show that the algorithm is very fast and allows the verification of
larger systems. We additionally implemented the use of state symmetries for
symbolic symmetry reduction. To our knowledge we are the first who investigated
state symmetries in combination with BDD based symbolic model checking
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
Analysing Mutual Exclusion using Process Algebra with Signals
In contrast to common belief, the Calculus of Communicating Systems (CCS) and
similar process algebras lack the expressive power to accurately capture mutual
exclusion protocols without enriching the language with fairness assumptions.
Adding a fairness assumption to implement a mutual exclusion protocol seems
counter-intuitive. We employ a signalling operator, which can be combined with
CCS, or other process calculi, and show that this minimal extension is
expressive enough to model mutual exclusion: we confirm the correctness of
Peterson's mutual exclusion algorithm for two processes, as well as Lamport's
bakery algorithm, under reasonable assumptions on the underlying memory model.
The correctness of Peterson's algorithm for more than two processes requires
stronger, less realistic assumptions on the underlying memory model.Comment: In Proceedings EXPRESS/SOS 2017, arXiv:1709.0004
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