Time-adaptive algorithms for synchronization

We consider concurrent systems in which there is an unknown upper bound on memory access time. Such a model is inherently different from asynchronous model where no such bound exists, and also from timing-based models where such a bound exists and is known a priori. The appeal of our model lies in the fact that while it abstracts from implementation details, it is a better approximation of real concurrent systems compared to the asynchronous model. Furthermore, it is stronger than the asynchronous model enabling us to design algorithms for problems that are unsolvable in the asynchronous model. Two basic synchronization problems, consensus and mutual exclusion, are investigated in a shared memory environment that supports atomic read/write registers. We show that \\Theta(\\Delta log \\Delta log log \\Delta ) is an upper and lower bound on the time complexity of consensus, where \\Delta is the (unknown) upper bound on memory access time. For the mutual exclusion problem, we design an effic...