No abstract

This paper shows for the first time that elimination, a scaling technique formerly applied only to counters and LIFO structures, can be applied to FIFO data structures, specifically, to linearizable FIFO queues. We show how to transform existing nonscalable FIFO queue implementations into scalable implementations using the elimination technique, while preserving lock-freedom and linearizablity.We apply our transformation to the FIFO queue algorithm of Michael and Scott, which is included in the Java TM Concurrency Package. Empirical evaluation on a state-ofthe-art CMT multiprocessor chip shows that by using elimination as a backoff technique for the Michael and Scott queue algorithm, we can achieve comparable performance at low loads, and improved scalability as load increases.

No abstract

A reaction of a distal dibromo diketocalix[4]arene with excess MeLi, followed by acid-catalyzed dehydration, yields a derivative with a pair of opposite exocyclic double bonds, and a pair of trans methyl groups at the bridges. A reaction of a tetrabromo calix[4]arene derivative with excess MeLi yields a calix[4]arene derivative with all methylene bridges monomethylated in all- cis fashion.

Lithiation of the calix[6]arene methyl ether 2 followed by reaction with O yields derivatives with two opposite methylene groups hydroxylated. Calix[6]arenes with two opposite bridges functionalized with alkoxy, azido, and m-xylyl groups were prepared via reaction of a dichlorocalix[6]arene derivative with nucleophiles.

Partial oxidation of the 1,3-alternate atropisomer of p-tert-butylcalix[4]arene tetraacetate with CrO3 afforded mainly a mixture of trioxo- and tetraoxo-calix[4]arene tetraacetate derivatives. The trioxotetrahydroxy derivative 6 was isolated from the mixture after hydrolysis of the crude product, followed by trituration with ethanol. Trioxocalix[4]arene adopts in the crystal a 1,2-alternate conformation. Acetylation or alkylation of the tetrahydroxytrioxocalix[4]arene 6 with acetic anhydride and 1-bromobutane, respectively, afforded exclusively a single atropisomer of the product, which in both cases were characterized as the 1,3-alternate form. Addition of MeLi to the tetramethyl and tetrabutyl ether of the trioxocalix[4]arenes followed by 3-fold elimination of water yielded calixarene derivatives possessing three exocyclic double bonds at the bridges. Reaction of the dioxotetramethoxy calix[4]arene 9b with MeLi followed by 2-fold elimination of water afforded calixarene 11 with a pair of distal exocyclic double bonds at the bridges. Both the tetramethyl ether derivatives 9b and 11 exist in solution as a mixture of the 1,2-alternate and 1,3-alternate conformers, but in the crystal both adopt a 1,2-alternate conformation.

We present the first lock-free implementation of an extensible hash table running on current architectures. It provides concurrent insert, delete, and search operations with an expected O(1) cost. It consists of very simple code, easily implementable using only load, store, and compare-and-swap operations. The new mathematical structure at the core of our algorithm is recursive split-ordering, a way of ordering elements in a linked list so that they can be repeatedly "split" using a single compare-and-swap operation. Empirical tests conducted on a large shared memory multiprocessor show that even in non-multiprogrammed environments, the new algorithm significantly outperforms the most efficient known lock-based algorithm at all concurrency levels, exhibiting up to four times higher throughput at peak load. The incremental nature of our algorithm makes it well suited for real-time applications, as it offers predictable performance without unexpected breaks for resizing.

No abstract