Eventually linearizable shared objects Serafini, Marco; Dobre, Dan; Majuntke, Matthias ...
Proceedings of the 29th ACM SIGACT-SIGOPS symposium on Principles of distributed computing,
07/2010
Conference Proceeding
Linearizability is the strongest known consistency property of shared objects. In asynchronous message passing systems, Linearizability can be achieved with ◊S and a majority of correct processes. In ...this paper we introduce the notion of Eventual Linearizability, the strongest known consistency property that can be attained with ◊S and any number of crashes. We show that linearizable shared object implementations can be augmented to support weak operations, which need to be linearized only eventually. Unlike strong operations that require to be always linearized, weak operations terminate in worst case runs. However, there is a tradeoff between ensuring termination of weak and strong operations when processes have only access to ◊S. If weak operations terminate in the worst case, then we show that strong operations terminate only in the absence of concurrent weak operations. Finally, we show that an implementation based on P exists that guarantees termination of all operations.
Automated software verification of concurrent programs is challenging because of exponentially large state spaces with respect to the number of threads and number of events per thread. Verification ...techniques such as model checking need to explore a large number of possible executions that are possible under a non-deterministic scheduler. State space reduction techniques such as partial order reduction simplify the verification problem, however, the reduced state space may still be exponentially large and intractable. This paper discusses \emph{Iteratively Relaxed Scheduling}, a framework that uses scheduling constraints in order to simplify the verification problem and enable automated verification of programs which could not be handled with fully non-deterministic scheduling. Program executions are safe as long as the same scheduling constraints are enforced under which the program has been verified, e.g., by instrumenting a program with additional synchronization. As strict enforcement of scheduling constraints may induce a high execution time overhead, we present optimizations over a naive solution that reduce this overhead. Our evaluation of a prototype implementation on well-known benchmark programs shows the effect of scheduling constraints on the execution time overhead and how this overhead can be reduced by relaxing and choosing constraints.
Rows of cells which flank the parasegment boundary make up a signaling center within the epidermis of the Drosophila embryo. Signals emanating from these cells, encoded by hedgehog and wingless are ...shown to be required for all segment pattern dorsally. Hedgehog is known to pattern the three cell types which compose one half of the parasegment and wingless is shown here to pattern the fourth cell type which comprises the other half of the segment. A genetic screen for mutants which affect this pattern was performed and the mutant lines is shown to lose wg-dependent cell types and to produce extra rows of cell types normally patterned by hh. Double mutant analysis shows that hh represses lines activity. A genetic model for dorsal patterning is proposed. Lines is also shown to be essential for ventral pattern and to be implicated in ventral cell types which are patterned by the DER pathway. Finally, cloning of the dna which contains the lines gene is demonstrated and this is confirmed by rescue of lines mutants with a genomic construct.
Software model checking 4 is a useful and practical branch of verification for verifying the implementation of the system. The wide usability comes at a price of low time and space efficiency. In ...fact, model checking of even simple single-process programs can take several hours using state-of-the-art techniques 6. Verification complexity gets even worse for concurrent programs that simultaneously execute loosely coupled processes. Verification efficiency can be greatly improved by capturing the state of the program, a technique generally referred to as stateful model checking 2. Intuitively, state capture enables to detect that two states are identical and, therefore, to consider only a representative state for verification. Unfortunately, capturing the state in general software systems can be very hard, even if the entire state of the system resides in the (local) memory. As a result, certain verification approaches (commonly called stateless model checking) do not capture the system’s state at all 4. Stateful model checking is in principle possible for software, however, at a price of considerable overhead. Therefore, stateful model checking is efficient only if the achieved reduction of redundantly explored states compensate for the overhead.
This thesis deals with efficient formal verification of fault-tolerant distributed protocols. The main focus is on protocols that achieve fault-tolerance using replication in distributed systems. In ...addition, communication in the distributed system is abstracted using message-passing. However, most of the concepts and solutions discussed in the thesis apply beyond replication-based message-passing protocols.
The outcome of verification is two-fold: Either the verification proves that the system (protocol) satisfies its specification or it returns (or claims the existence) of a counterexample that witnesses that the system (protocol) violates the specification. Both the development and application of fault-tolerant message-passing protocols can benefit from verification. Firstly, these protocols can be complex conceptual designs and hard to implement due to (i) a rich variety of (even malicious) faults that should be tolerated by the protocol and (ii) the concurrency in the distributed system executing the protocol. Therefore, counterexamples returned by verification in the phase of development can help developers to get the conceptual protocol and its implementation right. Secondly, fault-tolerant messages-passing protocols specify strong guarantees such as atomic broadcast or diagnosis of malicious faults. Therefore, the verification of such protocols can avoid failures of highly available systems that build upon these protocols.
The complexity of verification strongly depends on the size and nature of the system. Therefore, verification should be efficient in terms of space, time, and human interaction (ranging from full automation to requiring intuitive human guidance). Due to (i) and (ii), the verification of fault-tolerant message-passing protocols faces with a large problem space. Hence, straightforward verification approaches are inefficient. The thesis enables efficient verification of fault-tolerant message-passing systems in several ways.
The input of verification is a model of the system. The model represents the system and can be of varying resolution, e.g., source code, binaries, or high-level executable pseudocode. The efficiency of verification can significantly differ for different models of the same system. In the first part of the thesis, models of fault-tolerant message-passing protocols are proposed to enable efficient verification.
The proposed models address different aspects of fault-tolerant message-passing protocols. These aspects include (A1) message traffic -- an equivalence is shown between different models of sending, delivering, and consuming messages, which allows to select the model that is most amenable to efficient verification; (A2) fault-model -- a surprisingly simple and sound model of the widely-applied crash fault assumption is proposed allowing efficient verification of systems with crash faults; (A3) symmetries -- an approach for finding symmetries in the model is introduced, which can be exploited by symmetry reduction; and (A4) partial orders -- an equivalent translation of models is proposed to improve on the efficiency of partial-order reduction. Symmetry and partial-order reductions are general tools for efficient verification whose efficiency strongly depends on the model in use.
The second part of the thesis improves on existing verification techniques to enhance their efficiency.
The first technique is partial-order reduction, whose performance is limited by the poor flexibility and usability, and high time overhead of existing implementations. A new implementation of partial-order reduction is presented, called LPOR, that improves on all these features at the same time. To demonstrate the features of LPOR, it is applied to general message-passing systems. Experiments with representative fault-tolerant message-passing protocols justify LPOR's improvements. In addition, LPOR is implemented as an open-source Java library. This implementation is applied in MP-Basset, a model checker for general message-passing systems developed in the context of this thesis.
The second verification technique is automated induction. The efficiency of induction is limited by its general incompleteness, i.e., induction might return spurious (wrong) counterexamples for systems that satisfy the specification. A solution against spurious counterexamples is using lemmas. However, the discovery of lemmas is, in general, hard to automate. The thesis proposes a classification of lemmas in fault-tolerant message-passing protocols to enable their automated discovery. An example protocol is verified using classified lemmas and machine-checked induction proofs. Finally, a new approach, called strengthened transitions, is proposed to combat spurious counterexamples. An application of strengthened transitions for general multi-process systems is also presented.
Salkaházi Sára 1944-ben a Szociális Testvérek Társaságának, Bokréta utcai Munkásnők Otthonát vezette. Az otthon mintegy 150 állandó lakója között a nyilas-hatalomátvételkor legalább 25-30-an iratok ...nélkül vagy hamis iratokkal bujkáltak. Salkaházi Sárát egy feljelentés nyomán a nyilasok 1944 december 27-én elhurcolták és másokkal együtt a Dunába lőtték.
Carcass characteristics were studied in 80 young Hungarian red deer in different ages (12, 15, 18 and 20 months of age). In all age group 10 male and 10 female were slaughtered. The dressed carcass ...weight in skin varied between 53.72 and 65.66% of live weight. The first class lean meat varied between 14.3 and 16.6% of live weight. The live weight, carcass weight increased with the age and differed also between sexes. The highest dressing percentages were found at 20 months of age in both sexes (♂: 65.7%, ♀: 62.5%). Mainly the hinds had higher loin, leg and shoulder proportions of carcass at 20 months of age than the stags. The carcass muscle, bone and fat content were measured by computer tomography. These traits were grown and their proportion changed with the age. The bone to muscle ratio gradually decreased with the age while the fat to muscle ratio increased after 15 months of age (♂: from 0.13 to 0.17, ♀: from 0.15 to 0.18). At 18 month of age the hinds had higher bone to muscle and fat to muscle ratio than the stags'. The fat percentage of carcasses increased with the age in both sexes (♂: from 8.01% to 11.04%, ♀: from 8.40% to 11.28%). The hinds had higher values than the stags but it was significant just at 20 months of age. From the meat quality attributes there were found differences between ages in the case of pH, lightness, drip loss, cooking loss and shear force. The highest pH was found at 12 months of age in both sexes. There were found 5% intermediate pH (6.2 < pH < 5.8) at 12 and 15 months of age, all of them were male. The highest lightness values were observed at 18 months of age in both sexes (♂: 13.47, ♀: 14.90). There were differences between sexes in pH at all ages, except 15 months of age, and at 18 months of age in redness and lightness. Based on our results, the optimal slaughtering time for Hungarian red deer is 20 months of age, because this is when the dressing percentage is the best for both sexes. Meat quality traits changed with age, and gender differences sexes were the most pronounced for these traits at 18 months of age.
Ruthenium complexes are developed as substitutes for platinum complexes to be used in the chemotherapy of hematological and gynecological malignancies, such as ovarian cancer. We synthesized and ...screened 14 ruthenium half-sandwich complexes with bidentate monosaccharide ligands in ovarian cancer cell models. Four complexes were cytostatic, but not cytotoxic on A2780 and ID8 cells. The IC50 values were in the low micromolar range (the best being 0.87 µM) and were similar to or lower than those of the clinically available platinum complexes. The active complexes were cytostatic in cell models of glioblastoma, breast cancer, and pancreatic adenocarcinoma, while they were not cytostatic on non-transformed human skin fibroblasts. The bioactive ruthenium complexes showed cooperative binding to yet unidentified cellular target(s), and their activity was dependent on reactive oxygen species production. Large hydrophobic protective groups on the hydroxyl groups of the sugar moiety were needed for biological activity. The cytostatic activity of the ruthenium complexes was dependent on reactive species production. Rucaparib, a PARP inhibitor, potentiated the effects of ruthenium complexes.
Platinum complexes are used in chemotherapy, primarily as antineoplastic agents. In this study, we assessed the cytotoxic and cytostatic properties of a set of osmium(II), ruthenium(II), iridium(III) ...and rhodium(III) half-sandwich-type complexes with bidentate monosaccharide ligands. We identified 5 compounds with moderate to negligible acute cytotoxicity but with potent long-term cytostatic activity. These structure-activity relationship studies revealed that: (1) osmium(II)
-cymene complexes were active in all models, while rhodium(III) and iridium(III) Cp* complexes proved largely inactive; (2) the biological effect was influenced by the nature of the central azole ring of the ligands-1,2,3-triazole was the most effective, followed by 1,3,4-oxadiazole, while the isomeric 1,2,4-oxadiazole abolished the cytostatic activity; (3) we found a correlation between the hydrophobic character of the complexes and their cytostatic activity: compounds with
-benzoyl protective groups on the carbohydrate moiety were active, compared to
-deprotected ones. The best compound, an osmium(II) complex, had an IC
value of 0.70 µM. Furthermore, the steepness of the inhibitory curve of the active complexes suggested cooperative binding; cooperative molecules were better inhibitors than non-cooperative ones. The cytostatic activity of the active complexes was abolished by a lipid-soluble antioxidant, vitamin E, suggesting that oxidative stress plays a major role in the biological activity of the complexes. The complexes were active on ovarian cancer, pancreatic adenocarcinoma, osteosarcoma and Hodgkin's lymphoma cells, but were inactive on primary, non-transformed human fibroblasts, indicating their applicability as potential anticancer agents.
PDF