chubbymaggie / agency

Execution primitives for C++

Agency

Agency is an experiment exploring how to marry bulk synchronous parallel programming with the components described in the Technical Specification for C++ Extensions for Parallelism. The programming model Agency embodies is intended to be suited to all parallel architectures and is particularly exploitable by wide architectures exposing fine-grained parallelism.

The bulk_invoke function creates groups of execution agents which all invoke a lambda en masse:

template<class Iterator, class T, class BinaryFunction>
T reduce(Iterator first, Iterator last, T init, BinaryFunction binary_op)
{
  using namespace agency;
  auto n = std::distance(first, last);

  // reduce partitions of data into partial sums
  auto partial_sums = bulk_invoke(par, [=](parallel_agent& g)
  {
    auto i = g.index();
    auto partition_size = (n + g.group_size() - 1) / g.group_size();

    auto partition_begin = first + partition_size * i;
    auto partition_end   = std::min(last, partition_begin + partition_size);

    return reduce(seq, partition_begin + 1, partition_end, *partition_begin, binary_op);
  });

  return reduce(seq, partial_sums.begin(), partial_sums.end(), init, binary_op);
}

Design Goals

The design of the library is intended to achieve the following goals:

• Deliver efficiency by exploiting structured concurrency and sharing

• Build upon the execution policy approach introduced by the Parallelism TS

• Interface to the underlying platform via executors

• Provide a mechanism for controlling the placement of work to be created

Building the Example Programs

Programs with filenames ending in the .cpp extension are compilable with a C++11 compiler, e.g.:

$ g++ -std=c++11 -I. -pthread example.cpp

or

$ clang -std=c++11 -I. -pthread -lstdc++ example.cpp

or

$ icc -std=c++11 -I. -pthread example.cpp

Programs with filenames ending in the .cu extension are compilable with the NVIDIA compiler, e.g.:

$ nvcc -std=c++11 -I. example.cu

These programs are known to compile with g++ v4.8, clang v3.5, nvcc v8.0, and icc 15.0.