README.md

DIY is a block-parallel library

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.

Licensing

DIY is released as open source software under a BSD-style license.

Dependencies

DIY requires an MPI installation. We recommend MPICH.

Download, build, install

• You can clone this repository, or

• You can download the latest tarball.

DIY is a header-only library. It does not need to be built; you can simply include it in your project. The examples can be built using cmake from the top-level directory.

Development

Development happens in the DIY repo on Kitware's GitLab. Please submit merge requests there. Issues should be submitted in the GitHub repo.

Documentation

DIY project

Example

A simple DIY program, shown below, consists of the following components:

• structs called blocks,
• a diy object called the master,
• a set of callback functions performed on each block by master.foreach(),
• optionally, one or more message exchanges between the blocks by master.exchange(), and
• there may be other collectives and global reductions not shown below.

The callback functions (enqueue_local() and average() in the example below) receive the block pointer and a communication proxy for the message exchange between blocks. It is usual for the callback functions to enqueue or dequeue messages from the proxy, so that information can be received and sent during rounds of message exchange.

    // --- main program --- //

    struct Block { float local, average; };             // define your block structure

    Master master(world);                               // world = MPI_Comm
    ...                                                 // populate master with blocks
    master.foreach(&enqueue_local);                     // call enqueue_local() for each block
    master.exchange();                                  // exchange enqueued data between blocks
    master.foreach(&average);                           // call average() for each block

    // --- callback functions --- //

    // enqueue block data prior to exchanging it
    void enqueue_local(Block* b,                        // current block
                       const Proxy& cp)                 // communication proxy provides access to the neighbor blocks
    {
        for (size_t i = 0; i < cp.link()->size(); i++)  // for all neighbor blocks
            cp.enqueue(cp.link()->target(i), b->local); // enqueue the data to be sent to this neighbor
                                                        // block in the next exchange
    }

    // use the received data after exchanging it, in this case compute its average
    void average(Block* b,                              // current block
                 const Proxy& cp)                       // communication proxy provides access to the neighbor blocks
    {
        float x, average = 0;
        for (size_t i = 0; i < cp.link()->size(); i++)  // for all neighbor blocks
        {
            cp.dequeue(cp.link()->target(i).gid, x);    // dequeue the data received from this
                                                        // neighbor block in the last exchange
            average += x;
        }
        b->average = average / cp.link()->size();
    }