72,643 research outputs found
Modelling Garbage Collection Algorithms --- Extend abstract
We show how abstract requirements of garbage collection can be captured using temporal logic. The temporal logic specification can then be used as a basis for process algebra specifications which can involve varying amounts of parallelism. We present two simple CCS specifications as an example, followed by a more complex specification of the cyclic reference counting algorithm. The verification of such algorithms is then briefly discussed
Incremental garbage collection in massive object stores
© 2001 IEEEThere are only a few garbage collection algorithms that have been designed to operate over massive object stores. These algorithms operate at two levels, locally via incremental collection of small partitions and globally via detection of cross partition garbage, including cyclic garbage. At each level there is a choice of collection mechanism. For example, the PMOS collector employs tracing at the local level and reference counting at the global level. Another approach implemented in the Thor object database uses tracing at both levels. In this paper we present two new algorithms that both employ reference counting at the local level. One algorithm uses reference counting at the higher level and the other uses tracing at the higher level. An evaluation strategy is presented to support comparisons between these four algorithms and preliminary experiments are outlined
Practical distributed garbage collection for networks with asynchronous clocks and message delay
Distributed garbage collection over a message passage network is discussed in this paper. Traditionally, this can be done by reference counting, which is fast but cannot reclaim cyclic structures or by graph traversal, e.g. mark-and-sweep or time stamping, which is capable of reclaiming cyclic structures but is slow. We propose a combined scheme which is fast in reclaiming acyclic garbage and guaranteed to reclaim cyclic garbage. Our scheme does not rely on synchronized clocks nor zero message delay and is thus practical.published_or_final_versio
The effect of the number of response cycles on the behaviour of reinforced concrete elements subject to cyclic loading
The development of damage in reinforced concrete (RC) structures is a cumulative process. Some damage
indices used to quantify damage make use of the number of response cycles as an Engineering Demand
Parameter (EDP) relating with damage development. Other indices make use of deformation in terms of
displacement or chord rotation. These functions are generally a function of whether the response is monotonic or
cyclic, and are insensitive to the number of major deflection cycles leading to that state of damage. Many such
relations are derived from experimental data from low-cycle fatigue tests performed on RC elements. The
loading in such tests generally consists of either a monotonic increase in load or a gradually increasing cyclic
load. Since damage development is a cumulative process, and hence depends on the load history, the loading
pattern in low-cycle fatigue tests for assessment purposes should reflect the response of an earthquake. This
paper will discuss a procedure to determine a loading history for cyclic tests, based on earthquake demands. The
preliminary results of a campaign of low-cycle fatigue tests on RC elements to investigate the effect of using
different load histories are also discussed
A Cyclic Distributed Garbage Collector for Network Objects
This paper presents an algorithm for distributed garbage collection and outlines its implementation within the Network Objects system. The algorithm is based on a reference listing scheme, which is augmented by partial tracing in order to collect distributed garbage cycles. Processes may be dynamically organised into groups, according to appropriate heuristics, to reclaim distributed garbage cycles. The algorithm places no overhead on local collectors and suspends local mutators only briefly. Partial tracing of the distributed graph involves only objects thought to be part of a garbage cycle: no collaboration with other processes is required. The algorithm offers considerable flexibility, allowing expediency and fault-tolerance to be traded against completeness
System Description for a Scalable, Fault-Tolerant, Distributed Garbage Collector
We describe an efficient and fault-tolerant algorithm for distributed cyclic
garbage collection. The algorithm imposes few requirements on the local
machines and allows for flexibility in the choice of local collector and
distributed acyclic garbage collector to use with it. We have emphasized
reducing the number and size of network messages without sacrificing the
promptness of collection throughout the algorithm. Our proposed collector is a
variant of back tracing to avoid extensive synchronization between machines. We
have added an explicit forward tracing stage to the standard back tracing stage
and designed a tuned heuristic to reduce the total amount of work done by the
collector. Of particular note is the development of fault-tolerant cooperation
between traces and a heuristic that aggressively reduces the set of suspect
objects.Comment: 47 pages, LaTe
Comparator with noise suppression
An apparatus for generating a single pulse the first time only that a noisy cyclic signal exceeds a reference level during a half-cycle is disclosed. For the positive half of a cycle of the noisy cyclic signal, a comparator and a multivibrator produce a fixed voltage output when the noisy cyclic signal first exceeds the reference level. A multivibrator stops the production of the fixed voltage output when the noisy cyclic signal next passes the zero voltage level in the negative direction. Consequently, a single pulse is generated indicating that the signal exceeded the reference level during that half-cycle. The comparator and multi-vibrator produce pulses whenever the noisy cyclic signal exceeds the reference level during the negative half-cycle
Synchronous Counting and Computational Algorithm Design
Consider a complete communication network on nodes, each of which is a
state machine. In synchronous 2-counting, the nodes receive a common clock
pulse and they have to agree on which pulses are "odd" and which are "even". We
require that the solution is self-stabilising (reaching the correct operation
from any initial state) and it tolerates Byzantine failures (nodes that
send arbitrary misinformation). Prior algorithms are expensive to implement in
hardware: they require a source of random bits or a large number of states.
This work consists of two parts. In the first part, we use computational
techniques (often known as synthesis) to construct very compact deterministic
algorithms for the first non-trivial case of . While no algorithm exists
for , we show that as few as 3 states per node are sufficient for all
values . Moreover, the problem cannot be solved with only 2 states per
node for , but there is a 2-state solution for all values .
In the second part, we develop and compare two different approaches for
synthesising synchronous counting algorithms. Both approaches are based on
casting the synthesis problem as a propositional satisfiability (SAT) problem
and employing modern SAT-solvers. The difference lies in how to solve the SAT
problem: either in a direct fashion, or incrementally within a counter-example
guided abstraction refinement loop. Empirical results suggest that the former
technique is more efficient if we want to synthesise time-optimal algorithms,
while the latter technique discovers non-optimal algorithms more quickly.Comment: 35 pages, extended and revised versio
Energy conservation, counting statistics, and return to equilibrium
We study a microscopic Hamiltonian model describing an N-level quantum system
S coupled to an infinitely extended thermal reservoir R. Initially, the system
S is in an arbitrary state while the reservoir is in thermal equilibrium at
temperature T. Assuming that the coupled system S+R is mixing with respect to
the joint thermal equilibrium state, we study the Full Counting Statistics
(FCS) of the energy transfers S->R and R->S in the process of return to
equilibrium. The first FCS describes the increase of the energy of the system
S. It is an atomic probability measure, denoted , concentrated
on the set of energy differences ( is
the spectrum of the Hamiltonian of S, is the length of the time interval
during which the measurement of the energy transfer is performed, and
is the strength of the interaction between S and R). The second FCS,
, describes the decrease of the energy of the reservoir R and
is typically a continuous probability measure whose support is the whole real
line. We study the large time limit of these two measures
followed by the weak coupling limit and prove that the
limiting measures coincide. This result strengthens the first law of
thermodynamics for open quantum systems. The proofs are based on modular theory
of operator algebras and on a representation of by quantum
transfer operators
Counting Co-Cyclic Lattices
There is a well-known asymptotic formula, due to W. M. Schmidt (1968) for the
number of full-rank integer lattices of index at most in .
This set of lattices can naturally be partitioned with respect to the
factor group . Accordingly, we count the number of full-rank
integer lattices such that is
cyclic and of order at most , and deduce that these co-cyclic lattices are
dominant among all integer lattices: their natural density is . The problem is motivated by
complexity theory, namely worst-case to average-case reductions for lattice
problems
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