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Parallel BGL MPI BSP Process Group

Contents

Introduction

The MPI mpi_process_group is an implementation of the process group interface using the Message Passing Interface (MPI). It is the primary process group used in the Parallel BGL at this time.

Where Defined

Header <boost/graph/distributed/mpi_process_group.hpp>

Reference

namespace boost { namespace graph { namespace distributed {

class mpi_process_group
{
public:
  typedef boost::mpi::communicator communicator_type;

  // Process group constructors
  mpi_process_group(communicator_type comm = communicator_type());
  mpi_process_group(std::size_t num_headers, std::size_t buffer_size,
                    communicator_type comm = communicator_type());

  mpi_process_group();
  mpi_process_group(const mpi_process_group&, boost::parallel::attach_distributed_object);

  // Triggers
  template<typename Type, typename Handler>
    void trigger(int tag, const Handler& handler);

  template<typename Type, typename Handler>
    void trigger_with_reply(int tag, const Handler& handler);

  trigger_receive_context trigger_context() const;

  // Helper operations
  void poll();
  mpi_process_group base() const;
};

// Process query
int process_id(const mpi_process_group&);
int num_processes(const mpi_process_group&);

// Message transmission
template<typename T>
  void send(const mpi_process_group& pg, int dest, int tag, const T& value);

template<typename T>
  void receive(const mpi_process_group& pg, int source, int tag, T& value);

optional<std::pair<int, int> > probe(const mpi_process_group& pg);

// Synchronization
void synchronize(const mpi_process_group& pg);

// Out-of-band communication
template<typename T>
  void send_oob(const mpi_process_group& pg, int dest, int tag, const T& value);

template<typename T, typename U>
  void
  send_oob_with_reply(const mpi_process_group& pg, int dest, int
                      tag, const T& send_value, U& receive_value);

template<typename T>
  void receive_oob(const mpi_process_group& pg, int source, int tag, T& value);

} } }

Since the mpi_process_group is an implementation of the process group interface, we omit the description of most of the functions in the prototype. Two constructors need special mentioning:

mpi_process_group(communicator_type comm = communicator_type());

The constructor can take an optional MPI communicator. As default a communicator constructed from MPI_COMM_WORLD is used.

mpi_process_group(std::size_t num_headers, std::size_t buffer_size,
                  communicator_type comm = communicator_type());

For performance fine tuning the maximum number of headers in a message batch (num_headers) and the maximum combined size of batched messages (buffer_size) can be specified. The maximum message size of a batch is 16*num_headers+buffer_size. Sensible default values have been found by optimizing a typical application on a cluster with Ethernet network, and are num_header=64k and buffer_size=1MB, for a total maximum batches message size of 2MB.


Copyright (C) 2007 Douglas Gregor

Copyright (C) 2007 Matthias Troyer