Transactional memory (TM) aims to bring the benefits of ACID transactions to the volatile world of program synchronization. Architectural trends are making software transactions more appealing, as more programmers struggle with the problems of locks as they exploit multi-core processors. This thesis applies TM, which until recently has been restricted to small benchmarks, to a large, real-life system: the Linux operating system kernel. I describe TxLinux, a version of Linux, which is the first OS to use transactional memory for synchronization. TxLinux runs on MetaTM, a simulator co-designed with TxLinux, which models an x86-based Hardware Transactional Memory (HTM) system. The TxLinux/MetaTM effort yields a characterization of real-life OS transactions, exposes previously unconsidered complications (including interaction with interrupts and stack memory) and allows sensitivity studies of various TM microarchitectural parameters. It also provides a flexible platform for future OS, TM and architecture research. Next, I examine ways to increase concurrency by investigating the factors that inhibit concurrency in existing TM models and systems. These include avoidable implementation limitations, overly restrictive serialization models, and inexpressive APIs. After examining the nature of each limitation, I propose a solution for each one. I postulate that the conventional wisdom that every transaction is "for itself" and primarily relates to other transactions by conflicting with them, is a pervasive misperception. This thesis aims to demonstrate that there are other ways of thinking about the relation of one transaction to another. I present three different transaction models to show how (i) co-existence, (ii) cooperation, and (iii) coordination, can each solve important problems facing TM programmers today. Co-existence of multiple transactions on the same processor is enabled using the suspended transactions model. This model, used by TxLinux, can reduce aborts and removes transaction length limitations imposed by interrupts. Cooperation of transactions that access the same data, using the dependence-aware transactions model, can transparently turn transaction aborts into commits. Drawing on serializability theory and notions of spheres of control (which predate ACID transactions), this model is able to accept more execution schedules than any existing TM design. Lastly, the coordination of multiple transactions in the coordinated sibling transactions model, provides programmers a simple and unified way of expressing intratransaction parallelism. This helps move transactions beyond being a drop-in replacement for locks (SLE-style) to instead helping programmers find more parallel work within their programs (both in speculative and non-speculative forms). All three models aim at increasing concurrency, while shifting complexity away from the programmer and into the TM system. I evaluate all three models, using either the MetaTM HTM, or one of the several software (STM) systems this thesis also develops. / text

Tyrimo objektas: e-agroverslo reiškinys. Tyrimo tikslas: išnagrinėti e-agroverslo reiškinį teoriniu ir praktiniu aspektu. Uždaviniai: 1. Atskleisti e-verslo ir e-agroverslo teorinius aspektus. 2. Išanalizuoti e-agroverslo reiškinį empiriniu tyrimų metodu t.y. atlikti apklausą ir nustatyti faktinę e-agroverslo padėtį Lietuvoje. 3. Išnagrinėti e-agroverslo reiškinį kiekvieno iš transakcijų modelių pagrindu ir pagrįsti internetinių technologijų taikymo transakcijose privalumus. Tyrimo metodai: analizuojant e-agroverslo reiškinį e-verslo transakcijų pagrindu buvo naudojami šie tyrimo metodai: mokslinės literatūros analizė ir sintezė, loginis apibendrinimas, anketinė apklausa ir sisteminė analizė. Tyrimo rezultatai: • pirmojoje darbo dalyje pateikta e-verslo samprata ir išanalizuota e-agroverslo koncepcija. • antrojoje darbo dalyje aptartas atliktas tyrimas t.y. išnagrinėti Kauno rajono gyventojų anketinės paklausos metu gauti duomenys. • trečioje dalyje išanalizuoti verslas-darbuotojui (B2E), verslas - vartotojui (B2C), vartotojas-verslui (C2B), verslas - verslui (B2B), verslas valdžios institucijoms (B2G) ir valdžios institucijos - verslui (G2B) transakcijų modelių taikymo e-agroversle ypatumai. Aptarta interneto prieigos stoka Lietuvos kaimo teritorijose bei įsigilinta į elektroninio marketingo diegimo e-agroverslo įmonėje perspektyvas. • šiuolaikinis e-agroverslas yra priverstas įgyvendinti naujas strategijas ir veikti žemės ūkiui naujoje - elektroninėje erdvėje, kuri... [toliau žr. visą tekstą] / Research object: the phenomenon of agribusiness. Research aim: to analyse e-agribusiness phenomenon theoretically and practically. Objectives: 1. To reveal theoretical aspects of e-business and e-agribusiness; 2. To perform empirical analysis of e-agribusiness, to execute survey in order to identify factual status of e-agribusiness in Lithuania. 3. To discuss the concept of e-agribusiness on the basis of all e-business transaction models and to substantiate the usage of internet technologies in the transactions. Research methods: analysis and synthesis of literature, logical generalization, survey and systemic analysis. Empirical study was based on logic and methodological setups of similar surveys. Research results: • Theoretical analysis of e-business and e-agribusiness concepts is performed in the first part of master thesis. • The overview and analysis of survey results are discussed on the second part of the thesis. • The implementation of e-business transaction models in e-agribusiness and overview of e-marketing strategies for e-business as well as the benefits of implementation of internet technologies are discussed on the third part of the thesis. • Nowadays e-agribusiness is obliged to implement new strategies and operate in new electronic network. Contrary to traditional agribusiness this network is very dynamic. Electronic data exchange and other forms of internet technology implementation in business transactions change the traditional - paper based -... [to full text]