HabaneroUPC++: a Compiler-free PGAS Library

The Partitioned Global Address Space (PGAS) programming models combine shared and distributed memory features, providing the basis for high performance and high productivity parallel programming environments. UPC++ [39] is a very recent PGAS implementation that takes a library-based approach and avoids the complexities associated with compiler transformations. However, this implementation does not support dynamic task parallelism and only relies on other threading models (e.g., OpenMP or pthreads) for exploiting parallelism within a PGAS place. In this paper, we introduce a compiler-free PGAS library called HabaneroUPC++, which supports a tighter integration of intra-place and inter-place parallelism than standard hybrid programming approaches. The library makes heavy use of C++11 lambda functions in its APIs. C++11 lambdas avoid the need for compiler support while still retaining the syntactic convenience of language-based approaches. The HabaneroUPC++ library implementation is based on a tight integration of the UPC++ library and the Habanero-C++ library, with new extensions to support the integration. The UPC++ library is used to provide PGAS communication and function shipping support using GASNet, and the Habanero-C++ library is used to provide support for intra-place work-stealing integrated with function shipping. We demonstrate the programmability and performance of our implementation using two benchmarks, scaled up to 6K cores. The insights developed in this paper promise to further enhance the usability and popularity of PGAS programming models.