Efficient Wait-Free Algorithms for Implementing LL/SC Objects

Over the past decade, a pair of instructions called load-linked (LL) and store-conditional (SC) have emerged as the most suitable synchronization instructions for the design of lock-free algorithms. However, current architectures do not support these instructions; instead, they support either CAS (e.g., UltraSPARC, Itanium, Pentium) or restricted versions of LL/SC (e.g., POWER4, MIPS, Alpha). Thus, there is a gap between what algorithm designers want (namely, LL/SC) and what multiprocessors actually support (namely, CAS or restricted LL/SC). To bridge this gap, this thesis presents a series of efficient, wait-free algorithms that implement LL/SC from CAS or restricted LL/SC

Efficiently Implementing a Large Number of LL/SC Objects

Over the past decade, a pair of instructions called load-linked (LL) and store-conditional (SC) have emerged as the most suitable synchronization instructions for the design of lock-free algorithms. However, current architectures do not support these instructions; instead, they support either CAS (e.g., UltraSPARC, Itanium) or restricted versions of LL/SC (e.g., POWER4, MIPS, Alpha). Thus, there is a gap between what algorithm designers want (namely, LL/SC) and what multiprocessors actually support (namely, CAS or RLL/RSC). To bridge this gap, a flurry of algorithms that implement LL/SC from CAS have appeared in the literature. The two most recent algorithms are due to Doherty, Herlihy, Luchangco, and Moir (2004) and Michael (2004). To implement M LL/SC objects shared by N processes, Doherty et al.\u27s algorithm uses only O(N + M) space, but is only non-blocking and not wait-free. Michael\u27s algorithm, on the other hand, is wait-free, but uses O(N^2 + M) space. The main drawback of his algorithm is the time complexity of the SC operation: although the expected amortized running time of SC is only O(1), the worst-case running time of SC is O(N^2). The algorithm in this paper overcomes this drawback. Specifically, we design a wait-free algorithm that achieves a space complexity of O(N^2 + M), while still maintaining the O(1) worst-case running time for LL and SC operations

Efficient and Practical Constructions of LL/SC Variables

Over the past decade, LL/SC have emerged as the most suitable synchronization instructions for the design of lock-free algorithms. However, current architectures do not support these instructions; instead, they support either CAS or RLL/RSC (e.g. POWER4, MIPS, SPARC, IA-64). To bridge this gap, this paper presents two efficient wait-free algorithms for implementing 64-bit LL/SC objects from 64-bit CAS or RLL/RSC objects. Our first algorithm is practical: it has a small, constant time complexity (of 4 for LL and 5 for SC) and a space overhead of only 4 words per process. This algorithm uses unbounded sequence numbers. For theoretical interest, we also present a more complex bounded algorithm that still guarantees constant time complexity and O(1) space overhead per process. The LL/SC primitive is free of the well-known ABA problem that afflicts CAS. By efficiently implementing LL/SC words from CAS words, this work presents an efficient general solution to the ABA problem

Universal Block Tridiagonalization in B(H) and Beyond

For H a separable infinite dimensional complex Hilbert space, we prove that every B(H) operator has a basis with respect to which its matrix representation has a universal block tridiagonal form with block sizes given by a simple exponential formula independent of the operator. From this, such a matrix representation can be further sparsified to slightly sparser forms; it can lead to a direct sum of even sparser forms reflecting in part some of its reducing subspace structure; and in the case of operators without invariant subspaces (if any exists), it gives a plethora of sparser block tridiagonal representations. An extension to unbounded operators occurs for a certain domain of definition condition. Moreover this process gives rise to many different choices of block sizes.Comment: 7 Page

High Prevalence and Resistance Patterns of Community-Associated Methicillin-Resistant Staphylococcus aureus in the Pomoravlje Region, Serbia

With a view to estimating the prevalence and resistance patterns of CA-MRSA in one region of Serbia, we performed an analysis of MRSA isolates from healthy people and hospitalised patients. The detection of CA-MRSA was carried out by SCCmec typing. In MRSA isolates from hospitalised patients SCCmec types IV and V were found in 76% of the strains. Similar percentage (80%) of CA-MRSA genotypes was present in healthy people. SCCmec type V harbouring MRSA was the most successful clone. Higher prevalence of type V in hospitalised patients to that in healthy people (70% vs 54%) may indicate nosocomial transmissions in at least some hospital units. All MRSA strains from hospitalised patients were resistant to one or more non-β-lactam antibiotics while 52% were multi-resistant. In isolates from healthy people, 16% were sensitive to all non-β-lactam antibiotics and 40% were multi-resistant. Similar percentage of multi-resistant CA- and HA-genotypes occurred in a particular environment (53% vs 50% in hospitalised patients, and 37.5% vs 37.5% in healthy people) indicating selective pressure of antibiotics as a leading force conferring antibiotic resistance. High prevalence of CA-MRSA and high resistance rate both in hospitals and the community suggest that this pathogen has been present in the Pomoravlje Region, central Serbia for years

Extended eigenvalues of composition operators

A complex scalar lambda is said to be an extended eigenvalue of a bounded linear operator A on a complex Hilbert space if there is a nonzero operator X such that AX = lambda XA. The results in this paper provide a full solution to the problem of computing the extended eigenvalues for those composition operators C-phi induced on the Hardy space H-2(D) by linear fractional transformations phi of the unit disk. (c) 2021 Universidad de Sevilla. Published by Elsevier IncThe first and fourth authors were supported by Ministerio de Ciencia, Innovacion y Universidades under Grant MTM 2015-63699-P, and by Fondo Europeo de Desarrollo Regional under Grant PGC2018-094215-B-I00. The second author was also supported by Fondo Europeo de Desarrollo Regional under Grant PGC2018-101514-B-I00, and by Junta de Andalucia under Grant FEDER-UCA18-108415. The first author visited Western Michigan University at an early stage of this research. He would like to acknowledge the warm hospitality received from the third author. He is grateful to the Mathematics Department of WMU for covering local expenses and for the commitment to this global engagement.The third author visited Universidad de Sevilla several times at later stages of this research. He would like to thank the first and fourth authors for making possible this cooperation. He also acknowledges the Ministerio de Ciencia, Innovacion y Universidades for the sponsorship under Grant MTM 2015-6399-P, and the people at Instituto de Matematicas for the organization of his visits

Extended eigenvalues for Cesàro operators

A complex scalar λ is said to be an extended eigenvalue of a bounded linear operator T on a complex Banach space if there is a nonzero operator X such that T X = λXT. Such an operator X is called an extended eigenoperator of T corresponding to the extended eigenvalue λ. The purpose of this paper is to give a description of the extended eigenvalues for the discrete Ces`aro operator C0, the finite continuous Ces`aro operator C1 and the infinite continuous Ces`aro operator C∞ defined on the complex Banach spaces ℓ p , Lp [0, 1] and L p [0, ∞) for 1 < p < ∞ by the expressions (C0f)(n): = 1 n + 1 Xn k=0 f(k), (C1f)(x): = 1 x Z x 0 f(t) dt, (C∞f)(x): = 1 x Z x 0 f(t) dt. It is shown that the set of extended eigenvalues for C0 is the interval [1, ∞), for C1 it is the interval (0, 1], and for C∞ it reduces to the singleton {1}.Ministerio de Economía y CompetitividadJunta de AndalucíaVicerrectorado de investigación (Universidad de Cádiz

Comparison of Essential Metals in Different Pork Meat Cuts from the Serbian Market

AbstractPork consumption in Serbia accounts for a large share of total meat consumption. Pork is valuable sources of nutrients. We analyzed metal content in three different cuts of pork collected from the Serbian market during 2014. Analyses of the following isotopes: zinc (66Zn), copper (63Cu) and iron (57Fe) were performed by ICP-MS. Our data show that Zn, Cu and Fe were present in significantly different levels in hind leg, loin and shoulder, and that shoulder meat was richest in the analyzed metals. The differing mineral status of different pork cuts implies differences in their nutritional benefits for the human diet

CLIMATE CHANGE: IMPACT ON MYCOTOXINS INCIDENCE AND FOOD SAFETY

Climate change may have an impact on the occurrence of food safety hazards along the entire agri-food chain, from farm to fork. The interactions between environmental factors and food contamination, food safety and foodborne diseases are very complex, dynamic and difficult to predict. Extreme weather conditions such as floods and droughts which have not occurred previously in Serbia, may be supporting factors to contamination of crops by various species of toxigenic fungi and related mycotoxins. Mycotoxins are a group of naturally occurring toxic chemical substances, produced mainly by microscopic filamentous fungal species that commonly grow on a number of crops and that cause adverse health effects when consumed by humans and animals. Recent drought and then flooding confirmed that Serbia is one of the few European countries with very high risk exposure to natural hazards, as well as that mycotoxins are one of the foodborne hazards most susceptible to climate change.Climate change may have an impact on the occurrence of food safety hazards along the entire agri-food chain, from farm to fork. The interactions between environmental factors and food contamination, food safety and foodborne diseases are very complex, dynamic and difficult to predict. Extreme weather conditions such as floods and droughts which have not occurred previously in Serbia, may be supporting factors to contamination of crops by various species of toxigenic fungi and related mycotoxins. Mycotoxins are a group of naturally occurring toxic chemical substances, produced mainly by microscopic filamentous fungal species that commonly grow on a number of crops and that cause adverse health effects when consumed by humans and animals. Recent drought and then flooding confirmed that Serbia is one of the few European countries with very high risk exposure to natural hazards, as well as that mycotoxins are one of the foodborne hazards most susceptible to climate change