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Eventually Linearizable Shared Objects
, 2010
"... 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 prop ..."
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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 are live 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.
Available and Stabilizing 2-3 Trees
, 2000
"... Transient faults corrupt the content and organization of data structures. A recovery technique dealing with such faults is stabilization, which guarantees, following some number of operations on the data structure, that content of the data structure is legitimate. Another notion of fault toleranc ..."
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Transient faults corrupt the content and organization of data structures. A recovery technique dealing with such faults is stabilization, which guarantees, following some number of operations on the data structure, that content of the data structure is legitimate. Another notion of fault tolerance is availability, which is the property that operations continue to be applied during the period of recovery after a fault, and successful updates are not lost while the data structure stabilizes to a legitimate state. The available, stabilizing 2-3 tree supports find, insert, and delete operations, each with O(lg n) complexity when the tree's state is legitimate and contains n items. For an illegitimate state, these operations have O(lg K) complexity where K is the maximum capacity of the tree. Within O(t) operations, the state of the tree is guaranteed to be legitimate, where t is the number of nodes accessible via some path from the tree's root at the initial state. This paper re...
Specifying Security Constraints with Relaxation Lattices
"... Large software systems used in practice typically exhibit more complex behavior than small well-understood programs. Often, such systems display degraded behavior as they react to changes in the environment. ..."
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Large software systems used in practice typically exhibit more complex behavior than small well-understood programs. Often, such systems display degraded behavior as they react to changes in the environment.
1 Graceful Degradation of Air Traffic Operations
, 801
"... Abstract — The introduction of new technologies and concepts of operation in the air transportation system is not possible, unless they can be proven not to adversely affect the system operation under not only nominal, but also degraded conditions. In extreme scenarios, degraded operations due to pa ..."
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Abstract — The introduction of new technologies and concepts of operation in the air transportation system is not possible, unless they can be proven not to adversely affect the system operation under not only nominal, but also degraded conditions. In extreme scenarios, degraded operations due to partial or complete technological failures should never endanger system safety. Many past system evolutions, whether ground-based or airborne, have been based on trial-and-error, and system safety was addressed only after a specific event yielded dramatic or neardramatic consequences. Future system evolutions, however, must leverage available computation, prior knowledge and abstract reasoning to anticipate all possible system degradations and prove that such degradations are graceful and safe. This paper is concerned with the graceful degradation of high-density, structured arrival traffic against partial or complete surveillance failures. It is shown that for equal performance requirements, some traffic configurations might be easier to handle than others, thereby offering a quantitative perspective on these traffic configurations’ ability to “gracefully degrade”. To support our work, we also introduce a new conflict resolution algorithm, aimed at solving conflicts involving many aircraft when aircraft position information is in the process of degrading. I.
A UAV Test and Development Environment Based on Dynamic System Reconfiguration
"... This paper describes ongoing research to develop a framework for implementing dynamically reconfiguring avionics and control systems for unmanned aerial vehicles (UAVs) and a test and development environment for experimental UAVs. The framework supports graceful degradation, where hardware and softw ..."
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This paper describes ongoing research to develop a framework for implementing dynamically reconfiguring avionics and control systems for unmanned aerial vehicles (UAVs) and a test and development environment for experimental UAVs. The framework supports graceful degradation, where hardware and software failures cause a reduction in the quality or capability of the control system but does not result in total system failure. The approach uses a graphical specification representing modular software interdependencies and a runtime system manager that reconfigures the system. The techniques are currently being
