k-Abortable Objects: Progress Under High Contention.

In this paper, we define k-abortable objects, the first kind of abortable objects [2, 7] that guarantee some degree of progress even under high contention. The definition is simple and natural: intuitively, an operation on a k-abortable object can abort only if k operations from distinct processes succeed during the execution of the aborted operation. We first show that k-abortable objects can easily implement k -lock-free objects, i.e., objects where at least k processes make progress [5], but in contrast to k-lock-free objects, k-abortable objects always return control. We then give an efficient universal construction for wait-free k-abortable objects shared by n processes that takes only O(k) steps per operation. We also give a (varOmega (log k))-steps lower bound for universal constructions of k-abortable objects shared by (n ge k) processes. Since every wait-free k-abortable object can implement its k-lock-free counterpart, our universal construction also provides a universal construction for k-lock-free objects.