Showing papers by "Rolf Fagerberg published in 1994"

Chromatic Priority Queues

Abstract: We investigate the problem of implementing a priority queue to be used in a parallel environment, where asynchronous processes have access to a shared memory. Chromatic trees are a generalization of red-black trees appropriate for applications in such an environment, and it turns out that an appropriate priority queue can be obtained via minor modifications of chromatic trees. As opposed to earlier proposals, our deletemin operation is worst-case constant time, and insert is carried out as a fast search and constant time update, followed by an amortized constant number of rebalancing operations, which can be performed later by other processes, one at a time. If a general delete is desired, it can be implemented as a fast search and constant time update, followed by an amortized constant number of rebalancing operations, which again can be performed later by other processes, one at time. The amortization results here extend the results previously obtained for chromatic search trees. Since our proposal differs from previous work in that the processes doing updates need not have an exclusive lock on the root at any point, the number of processes which can work on the structure at any one time is not limited by the height of the tree. In fact, parallelism of the order the size of the tree is possible. The results proven in this paper show that congestion is unlikely to be a problem with a chromatic priority queue. We also present some heuristics which can be used if one wishes to even further reduce the probability of any problem due to congestion. As always, when working in an asynchronous environment, a locking scheme is required. We have included one possible locking scheme, specifically tuned to this application.