Distributed Systems on the .NET Framework Platform

S rozvojem internetové komunikace a s tím související dostupností stále většího množství služeb postavených na různých technologiích, představují distribuované systémy řešení, jak tyto síťově dostupné služby integrovat a poskytnout je uživatelům v ucelené podobě. K tomuto účelu lze využít platformu .NET Framework, která přináší prostředí určené pro vývoj aplikací ve vysoce distribuovaném prostředí internetu a intranetu. Tato dizertační práce se zabývá problematikou přístupu ke sdíleným prostředkům v rámci distribuovaných systémů využívající platformu .NET. První část práce je věnována popisu základních principů distribuovaných systémů a technik platformy .NET, kterých lze užít pro implementaci těchto principů. Pro účely zpracování požadavků nejen v distribuovaných systémech mající obvykle asynchronní charakter bylo navrhnuto a realizováno univerzální rozhraní pro popis asynchronních operací rozšiřující standardní techniky platformy .NET. V rámci řešení problematiky přístupu ke sdíleným prostředkům byl navržen model pro přístup ke sdíleným prostředkům vycházející z principů objektově orientovaného programování spolu se základním algoritmem pro zamezení stavu uváznutí při využívání prostředků více procesy (vlákny) současně. Tento rozšiřitelný model byl úspěšně implementován a jeho funkčnost ověřena na základních scénářích přístupu ke sdíleným zdrojům. Implementovaný model umožňuje po prvotní definici prostředků s těmito prostředky následně pracovat jako s každými jinými objekty, kdy synchronizační mechanismy probíhají transparentně na pozadí.With the expansion of the Internet communication and related availability of increasing number of services built on different technologies, distributed systems represent a solution to integrate these network services and provide them to users in a coherent form. The .NET Framework which provides an environment for application development in a highly distributed environment of Internet and intranet can be used to achieve this goal. This PhD thesis deals with access to shared resources in the context of distributed systems using the .NET platform. The first part of the work is devoted to describing the basic principles of distributed systems and .NET platform techniques, which can be used for implementation of the principles. For the purposes of request processing having asynchronous nature not only in distributed systems a universal interface for the description of asynchronous operations was designed and implemented. The interface extends standard asynchronous techniques on the .NET platform. In order to address the issue of access to shared resources model was designed based on the principles of object-oriented programming, along with basic algorithm to avoid deadlock in the case of use resources by multiple processes (threads) simultaneously. This extendable model has been successfully implemented and its functionality verified in basic scenarios of access to shared resources. After the definition of resources and their dependencies the implemented model allows working with resources as with any other objects on .NET platform. The synchronization processes proceed transparently in background.

The Human Race Vs. the Minorities : Racism, anti-racism, and intelligent non-humans in the world architecture of speculative fiction

This dissertation examines the intelligent non-humans of speculative fiction, interrogating their relationship to the social construct of “race.” It seeks to provide a framework for answering questions about whether a given fictional group is racial and the degree to which making claims about intelligent non-humans contributes to real-world inequality and oppression. To accomplish these goals, the dissertation examines the most popular works of speculative fiction from the twentieth century with supporting examples from elsewhere throughout the genre. It analyzes those works with a focus on their world architecture, defined here as the collection of all details about the world and the events therein that can be established by an appeal to the text. It compares the world architecture of each work to real-world ideological frameworks, showing how the works reflect and renegotiate contemporary ideologies in structuring their fictional worlds. The analysis proceeds from establishing the link between intelligent nonhuman creatures and “race” to exploring the ends to which texts deploy that link. This process begins in chapter three, which compares numerous fundamental traits of various non-humans to contemporary beliefs about human races. It further explores parallels between beliefs in racial hierarchies and the underlying logic of racial mixedness. It establishes that the texts define intelligent non-humans in terms strongly reminiscent of those used by contemporary racists to define human racial divisions. It further reinforces this claim by an appeal to features such as racial taxonomy and “new racism” to show that as racist beliefs have evolved over the century in the real world, the portrayal of intelligent non-humans in speculative fiction has evolved to match. Chapter four takes the pattern of representation established in chapter three and extends it, drawing on concepts from Whiteness studies. By exploring concepts such as normativity, enterprise, gendered relationships to light and dark, color coding by pigmentation, and reproductive anxieties, chapter four reveals further nuance to the hierarchies established in chapter three. In particular, it shows the hierarchies extending in muted form between genders and humans of different skin tones. Many of these uses of Whiteness come despite attempts by the same texts to work against them. The chapter takes initial steps in exploring the use of racialized non-humans by arguing that using Whiteness to rationalize the hierarchies of the fictional world reinforces its use in rationalizing real-world hierarchies. Chapter five finally explores the deployment of this racialization by considering the anti-racist strategies each work engages with. Each work involves itself with a variety of relativist, universalist, and practice-oriented anti-racist strategies. Each involvement shows the willingness of the works to negotiate these strategies and a critical awareness of those strategies’ strengths and shortcomings. At the same time, the works show a productive (“producerly”) complexity, and I discuss how each engagement leaves opportunities for selective (“guerilla”) readings. This openness ensures the ideological compatibility of the works with a wide audience by remaining open to interpretations across a broad range of the political spectrum. Ultimately, the dissertation establishes sufficient ground to answer final questions, such as whether a given work might be considered “racist” or “antiracist,” a question it tackles based on various foci and meanings. Any answer as to whether the works are “racist” regarding human beings must be highly qualified. However, there is an undeniable “yes” to whether they are “racist” regarding intelligent non-humans. Intelligent non-humans are constructed in racial terms, while humans mainly exist in a normative position relative to them. Among humans, differences appear regarding enterprise and participation in gendered Whiteness. Nonetheless, these are patterned rather than explicit, and no inherent differences are directly ascribed to humans based on skin tone, while some are openly denied. At the same time, each work is undeniably anti-racist, yet this anti-racism and racism coexist comfortably and without contradiction, as each work opposes certain features of or associated with racism while casually embracing more fundamental aspects. This complexity and openness to race is typical of popular speculative fiction and shows that race matters, even when it does not exist

Distributed Object Invocation in OBIWAN

The need for sharing is well-known in a large number of distributed collaborative applications. These applications are difficult to develop for an environment in which network connections are slow and not reliable. For this purpos

OBIWAN: Design and Implementation of a Middleware Platform

Programming distributed applications supporting data sharing is very hard. In most middleware platforms, programmers must deal with system-level issues for which they do not have the adequate knowledge, e.g., object replication, abusive resource consumption by mobile agents, and distributed garbage collection. As a result, programmers are diverted from their main task: the application logic. In addition, given that such system-level issues are extremely error-prone, programmers spend innumerous hours debugging. We designed, implemented, and evaluated a middleware platform called OBIWAN that releases the programmer from the above mentioned system-level issues. OBIWAN has the following distinctive characteristics: 1) allows the programmer to develop applications using either remote object invocation, object replication, or mobile agents, according to the specific needs of applications, 2) supports automatic object replication (e.g., incremental on-demand replication, transparent object faulting and serving, etc.), 3) supports distributed garbage collection of useless replicas, and 4) supports the specification and enforcement of history-based security policies well adapted to mobile agents needs (e.g., preventing abusive resource consumption)

Mobility and Wireless Support in OBIWAN

The need for sharing is well known in a large number of distributed collaborative applications in a mobile environment. For this purpose, we have been developing a platform called OBIWAN that: i) allows the application programmer to decide the mechanism by which objects should be invoked, remote method invocation or invocation on a local replica, ii) allows incremental (ondemand) replication of large object graphs, iii) provides hooks for the application programmer to implement a set of application specific properties such as transactional support or updates dissemination, iv) supports the migration of execution flows allowing the implementation of mobile agents, and v) supports the concept of a computing dynamic horizon in which resources in a broader sense (memory, disks, printers, internet access, data and even code) can be found in other neighbor devices and used accordingly