Ethnonationalist Triads: Assessing the Influence of Kin Groups on Civil Wars

Although the case-based literature suggests that kin groups are prominent in ethnonationalist conflicts, quantitative studies of civil war onset have both overaggregated and underaggregated the role of ethnicity, by looking at civil war at the country level instead of among specific groups and by treating individual countries as closed units, ignoring groups' transnational links. In this article the authors integrate transnational links into a dyadic perspective on conflict between marginalized ethnic groups and governments. They argue that transnational links can increase the risk of conflict as transnational kin support can facilitate insurgencies and are difficult for governments to target or deter. The empirical analysis, using new geocoded data on ethnic groups on a transnational basis, indicates that the risk of conflict is high when large, excluded ethnic groups have transnational kin in neighboring countries, and it provides strong support for the authors' propositions on the importance of transnational ties in ethnonationalist conflict.</jats:p

Configurable Strategies for Work-stealing

Work-stealing systems are typically oblivious to the nature of the tasks they are scheduling. For instance, they do not know or take into account how long a task will take to execute or how many subtasks it will spawn. Moreover, the actual task execution order is typically determined by the underlying task storage data structure, and cannot be changed. There are thus possibilities for optimizing task parallel executions by providing information on specific tasks and their preferred execution order to the scheduling system. We introduce scheduling strategies to enable applications to dynamically provide hints to the task-scheduling system on the nature of specific tasks. Scheduling strategies can be used to independently control both local task execution order as well as steal order. In contrast to conventional scheduling policies that are normally global in scope, strategies allow the scheduler to apply optimizations on individual tasks. This flexibility greatly improves composability as it allows the scheduler to apply different, specific scheduling choices for different parts of applications simultaneously. We present a number of benchmarks that highlight diverse, beneficial effects that can be achieved with scheduling strategies. Some benchmarks (branch-and-bound, single-source shortest path) show that prioritization of tasks can reduce the total amount of work compared to standard work-stealing execution order. For other benchmarks (triangle strip generation) qualitatively better results can be achieved in shorter time. Other optimizations, such as dynamic merging of tasks or stealing of half the work, instead of half the tasks, are also shown to improve performance. Composability is demonstrated by examples that combine different strategies, both within the same kernel (prefix sum) as well as when scheduling multiple kernels (prefix sum and unbalanced tree search)

Data Structures for Task-based Priority Scheduling

Many task-parallel applications can benefit from attempting to execute tasks in a specific order, as for instance indicated by priorities associated with the tasks. We present three lock-free data structures for priority scheduling with different trade-offs on scalability and ordering guarantees. First we propose a basic extension to work-stealing that provides good scalability, but cannot provide any guarantees for task-ordering in-between threads. Next, we present a centralized priority data structure based on $k$-fifo queues, which provides strong (but still relaxed with regard to a sequential specification) guarantees. The parameter $k$ allows to dynamically configure the trade-off between scalability and the required ordering guarantee. Third, and finally, we combine both data structures into a hybrid, $k$-priority data structure, which provides scalability similar to the work-stealing based approach for larger $k$, while giving strong ordering guarantees for smaller $k$. We argue for using the hybrid data structure as the best compromise for generic, priority-based task-scheduling. We analyze the behavior and trade-offs of our data structures in the context of a simple parallelization of Dijkstra's single-source shortest path algorithm. Our theoretical analysis and simulations show that both the centralized and the hybrid $k$-priority based data structures can give strong guarantees on the useful work performed by the parallel Dijkstra algorithm. We support our results with experimental evidence on an 80-core Intel Xeon system

Remote-scope Promotion: Clarified, Rectified, and Verified

Modern accelerator programming frameworks, such as OpenCL, organise threads into work-groups. Remote-scope promotion (RSP) is a language extension recently proposed by AMD researchers that is designed to enable applications, for the first time, both to optimise for the common case of intra-work-group communication (using memory scopes to provide consistency only within a work-group) and to allow occasional inter-work-group communication (as required, for instance, to support the popular load-balancing idiom of work stealing). We present the first formal, axiomatic memory model of OpenCL extended with RSP. We have extended the Herd memory model simulator with support for OpenCL kernels that exploit RSP, and used it to discover bugs in several litmus tests and a work-stealing queue, that have been used previously in the study of RSP. We have also formalised the proposed GPU implementation of RSP. The formalisation process allowed us to identify bugs in the description of RSP that could result in well-synchronised programs experiencing memory inconsistencies. We present and prove sound a new implementation of RSP that incorporates bug fixes and requires less non-standard hardware than the original implementation. This work, a collaboration between academia and industry, clearly demonstrates how, when designing hardware support for a new concurrent language feature, the early application of formal tools and techniques can help to prevent errors, such as those we have found, from making it into silicon

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

Dynamics and Logics of Civil War

This article reviews the literature on civil war. We focus on the most recent period of scholarly activity, beginning in the early 2000s when the publication of prominent quantitative studies triggered a surge in the empirical research of civil war as a well-defined conceptual category. We identify three explanatory logics that have dominated much of this literature and that view civil wars as a consequence of greed, grievances, and opportunities, respectively. We evaluate the arguments and findings of these theoretical approaches with respect to each of the main phases of war: outbreak, wartime dynamics, conflict termination, and postwar recovery. The article concludes by identifying key challenges confronting future civil war research. In particular, we emphasize the continuing need to advance theories that bridge the main explanatory logics as well as the different phases of conflict. Researchers should also pay more attention to defining the appropriate spatiotemporal scope of their studies

The change of tide in political cooperation: a limited information model of European integration

European integration follows a puzzling stop-and-go pattern that traditional international reations theories cannot fully explain. The predominating paradigms only account for either the achievements or the setbacks of the integration process. An information based explanation makes it possible to move beyond structural accounts provided by realist and functionalist scholarship. Such an approach yields solid micro-level foundations of international bargaining and focuses on leaders' use of threats in negotiations about regional cooperation. Situations involving governments agreeing on the necessity of further integration, but disagreeing about its level, create room for strategic manipulation of information asymmetries. This type of uncertainty stems from the manipulator's information and control advantages concerning domestic costs. The analysis of different summit meetings demonstrates the empirical relevance of such maneuvers for the dynamics of European integratio

Nationalism and Bounded Integration: What It Would Take to Construct a European Demos

Nation-state; European identity; identity; minorities; democratization

Ulikhet, eksklusjon og borgerkrig [Inequality, Exclusion, and Civil War]

Much of the recent research on civil war treats explanations rooted in political and economic grievances with considerable suspicion and claims that there is little empirical evidence of any relationship between ethnicity or inequality and political violence. We argue that common indicators used in previous research fail to capture fundamental aspects of political exclusion and economic inequality that can motivate conflict. Through a statistical analysis of all civil wars since 1960, we show that our theoretically informed indicators of political discrimination and economic marginalization among ethnic groups are powerful predictors of civil war onset. Individual-based inequality indicators, in contrast, display only weak effects. This article in Norwegian is a revised and updated version of earlier work published in English