Diy is a block-parallel library for implementing scalable algorithms
that can execute both in-core and out-of-core. The same program can be
executed with one or more threads per MPI process, seamlessly
combining distributed-memory message passing with shared-memory thread
parallelism. The abstraction enabling these capabilities is block
parallelism; blocks and their message queues are mapped onto
processing elements (MPI processes or threads) and are migrated
between memory and storage by the diy runtime. Complex communication
patterns, including neighbor exchange, merge reduction, swap
reduction, and all-to-all exchange, are possible in- and out-of-core
in diy.