 
Summary: TimeAdaptive Algorithms for Synchronization \Lambda
Rajeev Alur y Hagit Attiya z Gadi Taubenfeld x
Abstract
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 timingbased 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 investi
gated 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 consen
sus, where \Delta is the (unknown) upper bound on memory access time. For the mutual
exclusion problem, we design an efficient algorithm that takes advantage of the fact that
some upper bound on memory access time exists. The solutions for both problems are
even more efficient in the absence of contention, in which case their time complexity is
a constant.
