@inproceedings{4381, abstract = {Cloud computing aims to give users virtually unlimited pay-per-use computing resources without the burden of managing the underlying infrastructure. We claim that, in order to realize the full potential of cloud computing, the user must be presented with a pricing model that offers flexibility at the requirements level, such as a choice between different degrees of execution speed and the cloud provider must be presented with a programming model that offers flexibility at the execution level, such as a choice between different scheduling policies. In such a flexible framework, with each job, the user purchases a virtual computer with the desired speed and cost characteristics, and the cloud provider can optimize the utilization of resources across a stream of jobs from different users. We designed a flexible framework to test our hypothesis, which is called FlexPRICE (Flexible Provisioning of Resources in a Cloud Environment) and works as follows. A user presents a job to the cloud. The cloud finds different schedules to execute the job and presents a set of quotes to the user in terms of price and duration for the execution. The user then chooses a particular quote and the cloud is obliged to execute the job according to the chosen quote. FlexPRICE thus hides the complexity of the actual scheduling decisions from the user, but still provides enough flexibility to meet the users actual demands. We implemented FlexPRICE in a simulator called PRICES that allows us to experiment with our framework. We observe that FlexPRICE provides a wide range of execution options-from fast and expensive to slow and cheap-- for the whole spectrum of data-intensive and computation-intensive jobs. We also observe that the set of quotes computed by FlexPRICE do not vary as the number of simultaneous jobs increases.}, author = {Henzinger, Thomas A and Tomar, Anmol and Singh, Vasu and Wies, Thomas and Zufferey, Damien}, location = {Miami, USA}, pages = {83 -- 90}, publisher = {IEEE}, title = {{FlexPRICE: Flexible provisioning of resources in a cloud environment}}, doi = {10.1109/CLOUD.2010.71}, year = {2010}, } @inproceedings{4382, abstract = {Transactional memory (TM) has shown potential to simplify the task of writing concurrent programs. Inspired by classical work on databases, formal definitions of the semantics of TM executions have been proposed. Many of these definitions assumed that accesses to shared data are solely performed through transactions. In practice, due to legacy code and concurrency libraries, transactions in a TM have to share data with non-transactional operations. The semantics of such interaction, while widely discussed by practitioners, lacks a clear formal specification. Those interactions can vary, sometimes in subtle ways, between TM implementations and underlying memory models. We propose a correctness condition for TMs, parametrized opacity, to formally capture the now folklore notion of strong atomicity by stipulating the two following intuitive requirements: first, every transaction appears as if it is executed instantaneously with respect to other transactions and non-transactional operations, and second, non-transactional operations conform to the given underlying memory model. We investigate the inherent cost of implementing parametrized opacity. We first prove that parametrized opacity requires either instrumenting non-transactional operations (for most memory models) or writing to memory by transactions using potentially expensive read-modify-write instructions (such as compare-and-swap). Then, we show that for a class of practical relaxed memory models, parametrized opacity can indeed be implemented with constant-time instrumentation of non-transactional writes and no instrumentation of non-transactional reads. We show that, in practice, parametrizing the notion of correctness allows developing more efficient TM implementations.}, author = {Guerraoui, Rachid and Henzinger, Thomas A and Kapalka, Michal and Singh, Vasu}, location = {Santorini, Greece}, pages = {263 -- 272}, publisher = {ACM}, title = {{Transactions in the jungle}}, doi = {10.1145/1810479.1810529}, year = {2010}, } @inproceedings{4388, abstract = {GIST is a tool that (a) solves the qualitative analysis problem of turn-based probabilistic games with ω-regular objectives; and (b) synthesizes reasonable environment assumptions for synthesis of unrealizable specifications. Our tool provides the first and efficient implementations of several reduction-based techniques to solve turn-based probabilistic games, and uses the analysis of turn-based probabilistic games for synthesizing environment assumptions for unrealizable specifications.}, author = {Chatterjee, Krishnendu and Henzinger, Thomas A and Jobstmann, Barbara and Radhakrishna, Arjun}, location = {Edinburgh, UK}, pages = {665 -- 669}, publisher = {Springer}, title = {{GIST: A solver for probabilistic games}}, doi = {10.1007/978-3-642-14295-6_57}, volume = {6174}, year = {2010}, } @inproceedings{4389, abstract = {Digital components play a central role in the design of complex embedded systems. These components are interconnected with other, possibly analog, devices and the physical environment. This environment cannot be entirely captured and can provide inaccurate input data to the component. It is thus important for digital components to have a robust behavior, i.e. the presence of a small change in the input sequences should not result in a drastic change in the output sequences. In this paper, we study a notion of robustness for sequential circuits. However, since sequential circuits may have parts that are naturally discontinuous (e.g., digital controllers with switching behavior), we need a flexible framework that accommodates this fact and leaves discontinuous parts of the circuit out from the robustness analysis. As a consequence, we consider sequential circuits that have their input variables partitioned into two disjoint sets: control and disturbance variables. Our contributions are (1) a definition of robustness for sequential circuits as a form of continuity with respect to disturbance variables, (2) the characterization of the exact class of sequential circuits that are robust according to our definition, (3) an algorithm to decide whether a sequential circuit is robust or not.}, author = {Doyen, Laurent and Henzinger, Thomas A and Legay, Axel and Nickovic, Dejan}, pages = {77 -- 84}, publisher = {IEEE}, title = {{Robustness of sequential circuits}}, doi = {10.1109/ACSD.2010.26}, year = {2010}, } @inproceedings{4390, abstract = {Concurrent data structures with fine-grained synchronization are notoriously difficult to implement correctly. The difficulty of reasoning about these implementations does not stem from the number of variables or the program size, but rather from the large number of possible interleavings. These implementations are therefore prime candidates for model checking. We introduce an algorithm for verifying linearizability of singly-linked heap-based concurrent data structures. We consider a model consisting of an unbounded heap where each vertex stores an element from an unbounded data domain, with a restricted set of operations for testing and updating pointers and data elements. Our main result is that linearizability is decidable for programs that invoke a fixed number of methods, possibly in parallel. This decidable fragment covers many of the common implementation techniques — fine-grained locking, lazy synchronization, and lock-free synchronization. We also show how the technique can be used to verify optimistic implementations with the help of programmer annotations. We developed a verification tool CoLT and evaluated it on a representative sample of Java implementations of the concurrent set data structure. The tool verified linearizability of a number of implementations, found a known error in a lock-free implementation and proved that the corrected version is linearizable.}, author = {Cerny, Pavol and Radhakrishna, Arjun and Zufferey, Damien and Chaudhuri, Swarat and Alur, Rajeev}, location = {Edinburgh, UK}, pages = {465 -- 479}, publisher = {Springer}, title = {{Model checking of linearizability of concurrent list implementations}}, doi = {10.1007/978-3-642-14295-6_41}, volume = {6174}, year = {2010}, } @inbook{4392, abstract = {While a boolean notion of correctness is given by a preorder on systems and properties, a quantitative notion of correctness is defined by a distance function on systems and properties, where the distance between a system and a property provides a measure of “fit” or “desirability.” In this article, we explore several ways how the simulation preorder can be generalized to a distance function. This is done by equipping the classical simulation game between a system and a property with quantitative objectives. In particular, for systems that satisfy a property, a quantitative simulation game can measure the “robustness” of the satisfaction, that is, how much the system can deviate from its nominal behavior while still satisfying the property. For systems that violate a property, a quantitative simulation game can measure the “seriousness” of the violation, that is, how much the property has to be modified so that it is satisfied by the system. These distances can be computed in polynomial time, since the computation reduces to the value problem in limit average games with constant weights. Finally, we demonstrate how the robustness distance can be used to measure how many transmission errors are tolerated by error correcting codes. }, author = {Cerny, Pavol and Henzinger, Thomas A and Radhakrishna, Arjun}, booktitle = {Time For Verification: Essays in Memory of Amir Pnueli}, editor = {Manna, Zohar and Peled, Doron}, pages = {42 -- 60}, publisher = {Springer}, title = {{Quantitative Simulation Games}}, doi = {10.1007/978-3-642-13754-9_3}, volume = {6200}, year = {2010}, } @inproceedings{4393, abstract = {Boolean notions of correctness are formalized by preorders on systems. Quantitative measures of correctness can be formalized by real-valued distance functions between systems, where the distance between implementation and specification provides a measure of “fit” or “desirability.” We extend the simulation preorder to the quantitative setting, by making each player of a simulation game pay a certain price for her choices. We use the resulting games with quantitative objectives to define three different simulation distances. The correctness distance measures how much the specification must be changed in order to be satisfied by the implementation. The coverage distance measures how much the implementation restricts the degrees of freedom offered by the specification. The robustness distance measures how much a system can deviate from the implementation description without violating the specification. We consider these distances for safety as well as liveness specifications. The distances can be computed in polynomial time for safety specifications, and for liveness specifications given by weak fairness constraints. We show that the distance functions satisfy the triangle inequality, that the distance between two systems does not increase under parallel composition with a third system, and that the distance between two systems can be bounded from above and below by distances between abstractions of the two systems. These properties suggest that our simulation distances provide an appropriate basis for a quantitative theory of discrete systems. We also demonstrate how the robustness distance can be used to measure how many transmission errors are tolerated by error correcting codes.}, author = {Cerny, Pavol and Henzinger, Thomas A and Radhakrishna, Arjun}, location = {Paris, France}, pages = {235 -- 268}, publisher = {Schloss Dagstuhl - Leibniz-Zentrum für Informatik}, title = {{Simulation distances}}, doi = {10.1007/978-3-642-15375-4_18}, volume = {6269}, year = {2010}, } @inproceedings{4395, abstract = {The problem of locally transforming or translating programs without altering their semantics is central to the construction of correct compilers. For concurrent shared-memory programs this task is challenging because (1) concurrent threads can observe transformations that would be undetectable in a sequential program, and (2) contemporary multiprocessors commonly use relaxed memory models that complicate the reasoning. In this paper, we present a novel proof methodology for verifying that a local program transformation is sound with respect to a specific hardware memory model, in the sense that it is not observable in any context. The methodology is based on a structural induction and relies on a novel compositional denotational semantics for relaxed memory models that formalizes (1) the behaviors of program fragments as a set of traces, and (2) the effect of memory model relaxations as local trace rewrite operations. To apply this methodology in practice, we implemented a semi- automated tool called Traver and used it to verify/falsify several compiler transformations for a number of different hardware memory models.}, author = {Burckhardt, Sebastian and Musuvathi, Madanlal and Singh, Vasu}, editor = {Gupta, Rajiv}, location = {Pahos, Cyprus}, pages = {104 -- 123}, publisher = {Springer}, title = {{Verifying local transformations on relaxed memory models}}, doi = {10.1007/978-3-642-11970-5_7}, volume = {6011}, year = {2010}, } @inproceedings{4396, abstract = {Shape analysis is a promising technique to prove program properties about recursive data structures. The challenge is to automatically determine the data-structure type, and to supply the shape analysis with the necessary information about the data structure. We present a stepwise approach to the selection of instrumentation predicates for a TVLA-based shape analysis, which takes us a step closer towards the fully automatic verification of data structures. The approach uses two techniques to guide the refinement of shape abstractions: (1) during program exploration, an explicit heap analysis collects sample instances of the heap structures, which are used to identify the data structures that are manipulated by the program; and (2) during abstraction refinement along an infeasible error path, we consider different possible heap abstractions and choose the coarsest one that eliminates the infeasible path. We have implemented this combined approach for automatic shape refinement as an extension of the software model checker BLAST. Example programs from a data-structure library that manipulate doubly-linked lists and trees were successfully verified by our tool.}, author = {Beyer, Dirk and Henzinger, Thomas A and Théoduloz, Grégory and Zufferey, Damien}, editor = {Rosenblum, David and Taenzer, Gabriele}, location = {Paphos, Cyprus}, pages = {263 -- 277}, publisher = {Springer}, title = {{Shape refinement through explicit heap analysis}}, doi = {10.1007/978-3-642-12029-9_19}, volume = {6013}, year = {2010}, }