UNITY and Büchi automata

UNITY is a model for concurrent specifications with a complete logic for proving progress properties of the form ``$P$ leads to $Q$''. UNITY is generalized to U-specifications by giving more freedom to specify the steps that are to be taken infinitely often. In particular, these steps can correspond to non-total relations. The generalization keeps the logic sound and complete. The paper exploits the generalization in two ways. Firstly, the logic remains sound when the specification is extended with hypotheses of the form ``$F$ leads to $G$''. As the paper shows, this can make the logic incomplete. The generalization is used to show that the logic remains complete, if the added hypotheses ``$F$ leads to $G$'' satisfy ``$F$ unless $G$''. The main result extends the applicability and completeness of UNITY logic to proofs that a given concurrent program satisfies any given formula of LTL, linear temporal logic, without the next-operator which is omitted because it is sensitive to stuttering. For this purpose, the program, written as a UNITY program, is extended with a number of boolean variables. The proof method relies on implementing the LTL formula, i.e., restricting the specification in such a way that only those runs remain that satisfy the formula. This result is a variation of the classical construction of a B\"uchi automaton for a given LTL formula that accepts precisely those runs that satisfy the formula

Trylock, a case for temporal logic and eternity variables

An example is given of a software algorithm that implements its specification in linear time temporal logic (LTL), but not in branching time temporal logic (CTL). In LTL, a prophecy of future behaviour is needed to prove the simulation. Eternity variables are used for this purpose. The final phase of the proof is a refinement mapping in which two threads exchange roles. The example is a software implementation of trylock in a variation of the fast mutual exclusion algorithm of Lamport (1987). It has been used fruitfully for the construction of software algorithms for high performance mutual exclusion

MCSH, a lock with the standard interface

The MCS lock of Mellor-Crummey and Scott (1991), 23 pages. is a very efficient first-come first-served mutual-exclusion algorithm that uses the atomic hardware primitives fetch-and-store and compare-and-swap. However, it has the disadvantage that the calling thread must provide a pointer to an allocated record. This additional parameter violates the standard locking interface, which has only the lock as a parameter. Hence, it is impossible to switch to MCS without editing and recompiling an application that uses locks.This article provides a variation of MCS with the standard interface, which remains FCFS, called MCSH. One key ingredient is to stack allocate the necessary record in the acquire procedure of the lock, so its life-time only spans the delay to enter a critical section. A second key ingredient is communicating the allocated record between the acquire and release procedures through the lock to maintain the standard locking interface. Both of these practices are known to practitioners, but our solution combines them in a unique way. Furthermore, when these practices are used in prior papers, their correctness is often argued informally. The correctness of MCSH is verified rigorously with the proof assistant PVS, and experiments are run to compare its performance with MCS and similar locks

Congenital aortic stenosis in adults: rate of progression and predictors of clinical outcome: Reply

Dear Editor,We thank Dr. Ramaraj for his interest in our analysis on the progression of congenital aortic stenosis. Age should be regarded as an important risk factor for faster stenosis progression. The mechanism for faster progression is probably valve calcification occurring at an earlier age, promoted by the abnormal mechanical and shear stresses associated with a bicuspid aortic valve. Recent insights into the pathogenesis of calcification of the aortic valve suggest that this is an active, rather than a passive process, with features reminiscent of atherosclerosis. Inflammation, lipid infiltration, dystrophic calcification, ossification, and endothelial dysfunction have been observed in both diseases. [...

The Role of Uncoupling Protein 3 in Human Physiology

Obesity is simply understood as an imbalance between energy intake and expenditure in favor of weight accretion. However, the human biological interface between food consumption and energy dissipation results in broad individual differences in eating behavior, physical activity, and efficiency of fuel storage and metabolism. In particular, the basal metabolic rate, which accounts for the greatest portion of overall energy expenditure, can vary almost twofold among individuals. Classically, three major biochemical systems are believed to contribute to basal thermogenesis: futile cycles, Na+/K+ATPase activity, and mitochondrial proton leak. The latter is the most important quantitative contributor and can explain up to 50% of the basal metabolic rate (1). The molecular basis of mitochondrial proton leak is unclear, despite its importance in the understanding of energy balance and its potential as a therapeutic target for obesity treatment. The article by Hesselink and colleagues in this issue of the JCI (2) addresses whether uncoupling protein 3 contributes to mitochondrial proton leak in human skeletal muscle