Lock-free Concurrent Data Structures

Concurrent data structures are the data sharing side of parallel programming. Data structures give the means to the program to store data, but also provide operations to the program to access and manipulate these data. These operations are implemented through algorithms that have to be efficient. In the sequential setting, data structures are crucially important for the performance of the respective computation. In the parallel programming setting, their importance becomes more crucial because of the increased use of data and resource sharing for utilizing parallelism. The first and main goal of this chapter is to provide a sufficient background and intuition to help the interested reader to navigate in the complex research area of lock-free data structures. The second goal is to offer the programmer familiarity to the subject that will allow her to use truly concurrent methods.Comment: To appear in "Programming Multi-core and Many-core Computing Systems", eds. S. Pllana and F. Xhafa, Wiley Series on Parallel and Distributed Computin

The Design, Implementation, and Refinement of Wait-Free Algorithms and Containers

My research has been on the development of concurrent algorithms for shared memory systems that provide guarantees of progress. Research into such algorithms is important to developers implementing applications on mission critical and time sensitive systems. These guarantees of progress provide safety properties and freedom from many hazards, such as dead-lock, live-lock, and thread starvation. In addition to the safety concerns, the fine-grained synchronization used in implementing these algorithms promises to provide scalable performance in massively parallel systems. My research has resulted in the development of wait-free versions of the stack, hash map, ring buffer, vector, and a multi-word compare-and-swap algorithms. Through this experience, I have learned and developed new techniques and methodologies for implementing non-blocking and wait-free algorithms. I have worked with and refined existing techniques to improve their practicality and applicability. In the creation of the aforementioned algorithms, I have developed an association model for use with descriptor-based operations. This model, originally developed for the multi-word compare-and-swap algorithm, has been applied to the design of the vector and ring buffer algorithms. To unify these algorithms and techniques, I have released Tervel, a wait-free library of common algorithms and containers. This library includes a framework that simplifies and improves the design of non-blocking algorithms. I have reimplemented several algorithms using this framework and the resulting implementation exhibits less code duplication and fewer perceivable states. When reimplementing algorithms, I have adapted their Application Programming Interface (API) specification to remove ambiguity and non-deterministic behavior found when using a sequential API in a concurrent environment. To improve the performance of my algorithm implementations, I extended OVIS\u27s Lightweight Distributed Metric Service (LDMS)\u27s data collection and transport system to support performance monitoring using perf_event and PAPI libraries. These libraries have provided me with deeper insights into the behavior of my algorithms, and I was able to use these insights to improve the design and performance of my algorithms

Concurrent Non-blocking Skip List Using Multi-word Compare and Swap Operation

We present a non-blocking lock-free implementation of skip list data structure using multi word compare and swap (CASN) operation. This operation is designed to work on arbitrary number of memory locations as a single atomic step. We discuss the implementation details of CASN operation which only utilizes the single word compare and swap atomic primitive found in most of the contemporary multiprocessor systems. Using this operation, we first design lock-free algorithms to implement various operations on linked list data structure, then extend it to design skip lists. Skip list is a probabilistic data structure composed of linked lists stacked together forming different levels. It provides expected logarithmic time search like balanced search trees, but without requiring rebalancing. The fundamental operations on a skip list data structure require traversing and updating a number of memory locations. Due to this nature of the data structure, using a powerful atomic primitive like CASN in its implementation simplifies the design and makes the concurrent reasoning easier. In addition to fundamental operations, we present a variety of other operations on linked list and skip list data structures and provide examples to support the correctness of the proposed algorithms

Coûts de Synchronization dans les Programmes Parallèles et les Structures de Donnèes Simultanées

To use the computational power of modern computing machines, we have to deal with concurrent programs. Writing efficient concurrent programs is notoriously difficult, primarily due to the need of harnessing synchronization costs. In this thesis, we focus on synchronization costs in parallel programs and concurrent data structures.First, we present a novel granularity control technique for parallel programs designed for the dynamic multithreading environment. Then in the context of concurrent data structures, we consider the notion of concurrency-optimality and propose the first implementation of a concurrency-optimal binary search tree that, intuitively, accepts a concurrent schedule if and only if the schedule is correct. Also, we propose parallel combining, a technique that enables efficient implementations of concurrent data structures from their parallel batched counterparts. We validate the proposed techniques via experimental evaluations showing superior or comparable performance with respect to state-of-the-art algorithms.From a more formal perspective, we consider the phenomenon of helping in concurrent data structures. Intuitively, helping is observed when the order of some operation in a linearization is fixed by a step of another process. We show that no wait-free linearizable implementation of stack using read, write, compare&swap and fetch&add primitives can be help-free, correcting a mistake in an earlier proof by Censor-Hillel et al. Finally, we propose a simple way to analytically predict the throughput of data structures based on coarse-grained locking.Pour utiliser la puissance de calcul des ordinateurs modernes, nous devons écrire des programmes concurrents. L’écriture de programme concurrent efficace est notoirement difficile, principalement en raison de la nécessité de gérer les coûts de synchronization. Dans cette thèse, nous nous concentrons sur les coûts de synchronisation dans les programmes parallèles et les structures de données concurrentes.D’abord, nous présentons une nouvelle technique de contrôle de la granularité pour les programmes parallèles conçus pour un environnement de multi-threading dynamique. Ensuite, dans le contexte des structures de données concurrentes, nous considérons la notion d’optimalité de concurrence (concurrency-optimality) et proposons la première implémentation concurrence-optimal d’un arbre binaire de recherche qui, intuitivement, accepte un ordonnancement concurrent si et seulement si l’ordonnancement est correct. Nous proposons aussi la combinaison parallèle (parallel combining), une technique qui permet l’implémentation efficace des structures de données concurrences à partir de leur version parallèle par lots. Nous validons les techniques proposées par une évaluation expérimentale, qui montre des performances supérieures ou comparables à celles des algorithmes de l’état de l’art.Dans une perspective plus formelle, nous considérons le phénomène d’assistance (helping) dans des structures de données concurrentes. On observe un phénomène d’assistance quand l’ordre d’une opération d’un processus dans une trace linéarisée est fixée par une étape d’un autre processus. Nous montrons qu’aucune implémentation sans attente (wait-free) linéarisable d’une pile utilisant les primitives read, write, compare&swap et fetch&add ne peut être “sans assistance” (help-free), corrigeant une erreur dans une preuve antérieure de Censor-Hillel et al. Finalement, nous proposons une façon simple de prédire analytiquement le débit (throughput) des structures de données basées sur des verrous à gros grains

The Frame Game: An Examination Of How The Local Print Media Framed The Issue Of Pension And Health Care Costs In Detroit\u27s Municipal Bankruptcy

Scholars suggest understanding media theory and media sociology are instrumental when discussing the question of media power. Most of the empirical work done in this area has centered on the “objective-functionalist paradigm” (McQuail, 1985). The purpose of this study is to explore how two urban local print media outlets framed a group of stakeholders, the pensioners, and the broken promise of the pension and healthcare benefits, during Detroit’s municipal bankruptcy. I conducted a content analysis of Detroit News and Detroit Free Press news articles for the period from August 2013 to July 2014, focusing primarily on thirty (30) key dates during this one-year cycle. This paper contributes to the literature by utilizing the content analysis research strategy, identifying the words and/or phrases used to explain how print media constructs the space between people (the pensioners) and structure (the pension payments, healthcare benefits and municipal bankruptcy). The people of the City of Detroit was able to construct their views about the structure of the municipal bankruptcy based on the published articles by the two local media outlets The objective of my research was to examine the Detroit News and Detroit Free Press to understand if they supported the objective-functionalist paradigm or the subjective-functionalist paradigm. I collected 569 articles from the Detroit News and 833 from the Detroit Free Press. Of the two outlets, the Detroit Free Press produced a slightly higher percentage of articles, 12.2% (n=102), that focused specifically on the pensioners’ situation, compared to the Detroit News at 11.2% (n=64). I would speculate that this slight difference in percentage was attributed to the Detroit Free Press providing a broader coverage of the bankruptcy itself, and not just the pensioners (retirees) situation. The articles from my analysis suggested the Detroit Free Press followed an objective (content) functionalist paradigm and the Detroit News followed the subjective (content) functionalist paradigm. Although both media outlets remained close in their respective structures of reporting, it was clear that print media does follow a structure of media power as suggested by Entman (1993:52) and uses this power “to select some aspects of a perceived reality and make them more salient in communicating text, in such a way as to promote a particular problem definition, causal interpretation, moral evaluation, and/or treatment recommendation.” In other words, frames are used to focus attention on certain pieces of information about a particular item of interest and highlighting its significance, in essence, making it more meaningful to its audiences

The Advocate, December 14, 1972

https://red.mnstate.edu/advocate/1401/thumbnail.jp