Section: New Results

Miscellaneous

• A. Charguéraud worked together with Umut Acar and Mike Rainey, as part of the ERC project DeepSea, on the developement of efficient data structures and algorithms targeting modern, shared memory multicore architectures. Two major results were obtained this year.

  The first result is a sequence data structure that provides amortized constant-time access at the two ends, and logarithmic time concatenation and splitting at arbitrary positions. These operations are essential for programming efficient computation in the fork-join model. Compared with prior work, this novel sequence data structure achieves excellent constant factors, allowing it to be used as a replacement for traditional, non-splittable sequence data structures. This data structure, called chunked sequence due to its use of chunks (fixed-capacity arrays), has been implemented both in C++ and in OCaml. It is described in a paper published at ESA [26] .

  Another result by A. Charguéraud and his co-authors is the development of fast and robust parallel graph traversal algorithms, more precisely for parallel BFS and parallel DFS. The new algorithms leverage the aforementioned sequence data structure for representing the set of edges remaining to be visited. In particular, it uses the split operation for balancing the edges among the several processors involved in the computation. Compared with prior work, these new algorithms are designed to be efficient not just for particular classes of graphs, but for all input graphs. This work has not yet been published, however it is described in details in a technical report [40] . Note that these two graph algorithms, which involve nontrivial use of concurrent data structures, will be very interesting targets for formal verification.