628 research outputs found
Data refinement for true concurrency
The majority of modern systems exhibit sophisticated concurrent behaviour, where several system components modify and observe the system state with fine-grained atomicity. Many systems (e.g., multi-core processors, real-time controllers) also exhibit truly concurrent behaviour, where multiple events can occur simultaneously. This paper presents data refinement defined in terms of an interval-based framework, which includes high-level operators that capture non-deterministic expression evaluation. By modifying the type of an interval, our theory may be specialised to cover data refinement of both discrete and continuous systems. We present an interval-based encoding of forward simulation, then prove that our forward simulation rule is sound with respect to our data refinement definition. A number of rules for decomposing forward simulation proofs over both sequential and parallel composition are developed
Simplifying proofs of linearisability using layers of abstraction
Linearisability has become the standard correctness criterion for concurrent
data structures, ensuring that every history of invocations and responses of
concurrent operations has a matching sequential history. Existing proofs of
linearisability require one to identify so-called linearisation points within
the operations under consideration, which are atomic statements whose execution
causes the effect of an operation to be felt. However, identification of
linearisation points is a non-trivial task, requiring a high degree of
expertise. For sophisticated algorithms such as Heller et al's lazy set, it
even is possible for an operation to be linearised by the concurrent execution
of a statement outside the operation being verified. This paper proposes an
alternative method for verifying linearisability that does not require
identification of linearisation points. Instead, using an interval-based logic,
we show that every behaviour of each concrete operation over any interval is a
possible behaviour of a corresponding abstraction that executes with
coarse-grained atomicity. This approach is applied to Heller et al's lazy set
to show that verification of linearisability is possible without having to
consider linearisation points within the program code
Reasoning algebraically about refinement on TSO architectures
The Total Store Order memory model is widely implemented by modern multicore architectures such as x86, where local buffers are used for optimisation, allowing limited forms of instruction reordering. The presence of buffers and hardware-controlled buffer flushes increases the level of non-determinism from the level specified by a program, complicating the already difficult task of concurrent programming. This paper presents a new notion of refinement for weak memory models, based on the observation that pending writes to a process' local variables may be treated as if the effect of the update has already occurred in shared memory. We develop an interval-based model with algebraic rules for various programming constructs. In this framework, several decomposition rules for our new notion of refinement are developed. We apply our approach to verify the spinlock algorithm from the literature
Deriving real-time action systems with multiple time bands using algebraic reasoning
The verify-while-develop paradigm allows one to incrementally develop programs from their specifications using a series of calculations against the remaining proof obligations. This paper presents a derivation method for real-time systems with realistic constraints on their behaviour. We develop a high-level interval-based logic that provides flexibility in an implementation, yet allows algebraic reasoning over multiple granularities and sampling multiple sensors with delay. The semantics of an action system is given in terms of interval predicates and algebraic operators to unify the logics for an action system and its properties, which in turn simplifies the calculations and derivations
Convolution, Separation and Concurrency
A notion of convolution is presented in the context of formal power series
together with lifting constructions characterising algebras of such series,
which usually are quantales. A number of examples underpin the universality of
these constructions, the most prominent ones being separation logics, where
convolution is separating conjunction in an assertion quantale; interval
logics, where convolution is the chop operation; and stream interval functions,
where convolution is used for analysing the trajectories of dynamical or
real-time systems. A Hoare logic is constructed in a generic fashion on the
power series quantale, which applies to each of these examples. In many cases,
commutative notions of convolution have natural interpretations as concurrency
operations.Comment: 39 page
Cultural Politics of Community-Based Conservation in the Buffer Zone of Chitwan National Park, Nepal
The dissertation research examines the socio-economic and political effects of community-based conservation initiatives within the Bagmara buffer zone community forests of Chitwan National Park, Nepal. In particular, the study investigates the role of buffer zones creation in structuring the way rural property rights have been defined, negotiated, and contested, in reinforcing or reducing patterns of ethnic dominance and exclusion, and in influencing how cultural identities are constituted and renegotiated. Using a political ecology framework with a specific focus on theoretical concepts of environmentality and territorialization, I conducted 12 months ethnographic and quantitative survey field research in the buffer zone communities of Chitwan National Park. I focused on documenting socioeconomic conditions and livelihood practices, and interpreting the meanings of residents’ lived experiences. In addition, I critically examined state and non-state conservation and development practices to understand how they work to produce identities, livelihoods, and landscapes in the park’s buffer zone.
The ethnographic study documented diverse impacts of community-based conservation initiatives. One of the major effects is the distribution of costs and benefits, specifically elite capture of community forest and tourism benefits. Second is the existing conflict and potential conflict over the control of access, benefits, and territory based on social and cultural identities. Third is the reproduction of caste, ethnic, and class hierarchies. Fourth is the militarization of communities in and around the buffer zone and community forest. Fifth is the production of environmental and non-environmental subjects such as illegals and poachers. Finally, the sixth is the commodification of conservation spaces and subsequent ecological impacts. The research concludes that the discursive representation of humans and non-humans and the discourses and practices of economic development and biodiversity conservation produced and reproduced a number of negative social, political, and ecological consequences in the buffer zone of CNP. This dissertation concluded that the conservation and development practices are territorial projects to govern people and nature
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