TIMPI::detail Namespace Reference

Functions
void	empty_send_assertion (const Communicator &comm, processor_id_type empty_target_pid)
template<typename MapToContainers , typename SendFunctor , typename PossiblyReceiveFunctor , typename ActionFunctor >
void	push_parallel_nbx_helper (const Communicator &comm, MapToContainers &&data, const SendFunctor &send_functor, const PossiblyReceiveFunctor &possibly_receive_functor, const ActionFunctor &act_on_data)
template<typename MapToContainers , typename SendFunctor , typename ReceiveFunctor , typename ActionFunctor >
void	push_parallel_alltoall_helper (const Communicator &comm, MapToContainers &&data, const SendFunctor &send_functor, const ReceiveFunctor &receive_functor, const ActionFunctor &act_on_data)
template<typename MapToContainers , typename SendReceiveFunctor , typename ActionFunctor >
void	push_parallel_roundrobin_helper (const Communicator &comm, MapToContainers &&data, const SendReceiveFunctor &sendreceive_functor, const ActionFunctor &act_on_data)

Function Documentation

empty_send_assertion()

void TIMPI::detail::empty_send_assertion ( const Communicator &  comm, processor_id_type  empty_target_pid  )

inline

Definition at line 218 of file parallel_sync.h.

References TIMPI::Communicator::max(), and TIMPI::Communicator::rank().

Referenced by push_parallel_alltoall_helper(), push_parallel_nbx_helper(), and push_parallel_roundrobin_helper().

{
  bool someone_found_empty_send = (empty_target_pid != processor_id_type(-1));
  comm.max(someone_found_empty_send);
  std::stringstream err_msg;
  if (empty_target_pid != processor_id_type(-1))
    err_msg << " [" << comm.rank() << "] sent an empty to [" <<
      empty_target_pid << "]";
  timpi_assert_msg(!someone_found_empty_send,
                   "Some rank(s) sent empty data!" + err_msg.str());
}

push_parallel_alltoall_helper()

template<typename MapToContainers , typename SendFunctor , typename ReceiveFunctor , typename ActionFunctor >

void TIMPI::detail::push_parallel_alltoall_helper	(	const Communicator &	comm,
		MapToContainers &&	data,
		const SendFunctor &	send_functor,
		const ReceiveFunctor &	receive_functor,
		const ActionFunctor &	act_on_data
	)

Definition at line 449 of file parallel_sync.h.

References TIMPI::Communicator::alltoall(), TIMPI::any_source, empty_send_assertion(), TIMPI::Communicator::get_unique_tag(), TIMPI::Communicator::probe(), TIMPI::Communicator::rank(), and TIMPI::Communicator::size().

Referenced by TIMPI::push_parallel_packed_range(), and TIMPI::push_parallel_vector_data().

{
  typedef typename std::remove_reference<MapToContainers>::type::value_type::second_type
    container_type;

  // This function must be run on all processors at once
  timpi_parallel_only(comm);

  // This function implements a simpler asynchronous protocol than
  // NBX.  Every processor will know exactly how many receives to
  // post.

  processor_id_type num_procs = comm.size();

  // Don't give us empty vectors to send.  We'll yell at you (after
  // the sync is done, so all ranks get out of it and we can throw an
  // assertion failure everywhere) if we're debugging and we catch
  // one.
  //
  // But in opt mode we'll just skip empty vectors.
#ifndef NDEBUG
  processor_id_type empty_target_pid = processor_id_type(-1);
#endif

  // Number of vectors to send to each procesor
  std::vector<std::size_t> will_send_to(num_procs, 0);
  for (auto & datapair : data)
    {
      // In the case of data partitioned into more processors than we
      // have ranks, we "wrap around"
      processor_id_type dest_pid = datapair.first % num_procs;

      // But in opt mode we'll just try to stay consistent with what
      // we can do in the other backends
      if (datapair.second.empty())
        {
#ifndef NDEBUG
          empty_target_pid = dest_pid;
#endif
          continue;
        }

      will_send_to[dest_pid]++;
    }

  // Tell everyone about where everyone will send to
  comm.alltoall(will_send_to);

  // will_send_to now represents how many vectors we'll receive from
  // each processor; give it a better name.
  auto & will_receive_from = will_send_to;

  processor_id_type n_receives = 0;
  for (processor_id_type proc_id = 0; proc_id < num_procs; proc_id++)
    n_receives += will_receive_from[proc_id];

  // We'll grab a tag so we can overlap request sends and receives
  // without confusing one for the other
  MessageTag tag = comm.get_unique_tag();

  // The send requests
  std::list<Request> requests;

  // Post all of the non-empty sends, non-blocking
  for (auto & datapair : data)
    {
      processor_id_type destid = datapair.first % num_procs;
      auto & datum = datapair.second;

      if (datum.empty())
        continue;

      // Just act on data if the user requested a send-to-self
      if (destid == comm.rank())
        {
          act_on_data(destid, std::move(datum));
          n_receives--;
        }
      else
        {
          requests.emplace_back();
          send_functor(destid, datum, requests.back(), tag);
        }
    }

  // In serial we've now acted on all our data.
  if (num_procs == 1)
    return;

  // Post all of the receives.
  for (processor_id_type i = 0; i != n_receives; ++i)
    {
      Status stat(comm.probe(any_source, tag));
      const processor_id_type
        proc_id = cast_int<processor_id_type>(stat.source());

      container_type received_data;
      receive_functor(proc_id, received_data, tag);
      act_on_data(proc_id, std::move(received_data));
    }

  // Wait on all the sends to complete
  for (auto & req : requests)
    req.wait();

  // So, *did* we see any empty containers being sent?
#ifndef NDEBUG
  empty_send_assertion(comm, empty_target_pid);
#endif // NDEBUG
}

push_parallel_nbx_helper()

template<typename MapToContainers , typename SendFunctor , typename PossiblyReceiveFunctor , typename ActionFunctor >

void TIMPI::detail::push_parallel_nbx_helper	(	const Communicator &	comm,
		MapToContainers &&	data,
		const SendFunctor &	send_functor,
		const PossiblyReceiveFunctor &	possibly_receive_functor,
		const ActionFunctor &	act_on_data
	)

Definition at line 237 of file parallel_sync.h.

References TIMPI::any_source, empty_send_assertion(), TIMPI::Communicator::get_unique_tag(), TIMPI::Communicator::nonblocking_barrier(), TIMPI::Communicator::rank(), TIMPI::Communicator::send_mode(), TIMPI::Communicator::size(), TIMPI::Communicator::SYNCHRONOUS, TIMPI::Request::test(), and TIMPI::Request::wait().

Referenced by TIMPI::push_parallel_packed_range(), and TIMPI::push_parallel_vector_data().

{
  typedef typename std::remove_reference<MapToContainers>::type::value_type::second_type
    container_type;

  // This function must be run on all processors at once
  timpi_parallel_only(comm);

  // This function implements the "NBX" algorithm from
  // https://htor.inf.ethz.ch/publications/img/hoefler-dsde-protocols.pdf

  // We'll grab a tag so we can overlap request sends and receives
  // without confusing one for the other
  const auto tag = comm.get_unique_tag();

  // Save off the old send_mode so we can restore it after this
  const auto old_send_mode = comm.send_mode();

  // Set the sending to synchronous - this is so that we can know when
  // the sends are complete
  const_cast<Communicator &>(comm).send_mode(Communicator::SYNCHRONOUS);

  // The send requests
  std::list<Request> send_requests;

  const processor_id_type num_procs = comm.size();

  // Don't give us empty vectors to send.  We'll yell at you (after
  // the sync is done, so all ranks get out of it and we can throw an
  // assertion failure everywhere) if we're debugging and we catch
  // one.
  //
  // But in opt mode we'll just skip empty vectors.
#ifndef NDEBUG
  processor_id_type empty_target_pid = processor_id_type(-1);
#endif

  for (auto & datapair : data)
    {
      // In the case of data partitioned into more processors than we
      // have ranks, we "wrap around"
      processor_id_type dest_pid = datapair.first % num_procs;
      auto & datum = datapair.second;

      if (datum.empty())
        {
#ifndef NDEBUG
          empty_target_pid = dest_pid;
#endif
          continue;
        }

      // Just act on data if the user requested a send-to-self
      if (dest_pid == comm.rank())
        act_on_data(dest_pid, std::move(datum));
      else
        {
          send_requests.emplace_back();
          send_functor(dest_pid, datum, send_requests.back(), tag);
        }
    }

  // In serial we've now acted on all our data.
  if (num_procs == 1)
    return;

  // Whether or not the nonblocking barrier has started
  bool started_barrier = false;
  // Request for the nonblocking barrier
  Request barrier_request;

  struct IncomingInfo
  {
    unsigned int src_pid = any_source;
    Request request;
    container_type data;
  };

  // Storage for the incoming requests and data
  // The last entry in this list will _always_ be an invalid entry
  // that is available for use for processing the next incoming
  // request. That is, its size will always be >= 1
  std::list<IncomingInfo> incoming;
  incoming.emplace_back(); // add the first invalid entry for receives

  // Helper for checking and processing receives if there are any; we
  // need to check this in multiple places
  auto possibly_receive = [&incoming, &tag, &possibly_receive_functor]() {
    auto & next_incoming = incoming.back();
    timpi_assert_equal_to(next_incoming.src_pid, any_source);
    if (possibly_receive_functor(next_incoming.src_pid,
                                 next_incoming.data,
                                 next_incoming.request, tag))
      {
        timpi_assert(next_incoming.src_pid != any_source);

        // Insert another entry so that the next poll has something
        // to fill into if needed
        incoming.emplace_back();

        // We received something
        return true;
      }

      // We didn't receive anything
      return false;
  };

  // Keep looking for receives
  while (true)
    {
      timpi_assert(incoming.size() > 0);

      // Check if there is a message and start receiving it
      possibly_receive();

      // Work through the incoming requests and act on them if they're ready
      incoming.remove_if
        ([&act_on_data
#ifndef NDEBUG
          ,&incoming
#endif
          ](IncomingInfo & info)
          {
            // The last entry (marked by an invalid src pid) should be skipped;
            // it needs to remain in the list for potential filling in the next poll
            const bool is_invalid_entry = info.src_pid == any_source;
            timpi_assert_equal_to(is_invalid_entry, &info == &incoming.back());

            if (is_invalid_entry)
              return false;

            // If it's finished - let's act on it
            if (info.request.test())
              {
                // Do any post-wait work
                info.request.wait();

                // Act on the data
                act_on_data(info.src_pid, std::move(info.data));

                // This removes it from the list
                return true;
              }

              // Not finished yet
              return false;
            });

      // Remove any sends that have completed in user space
      send_requests.remove_if
        ([](Request & req)
         {
           if (req.test())
             {
               // Do Post-Wait work
               req.wait();
               return true;
             }

             // Not finished yet
             return false;
         });

      // If all of the sends are complete, we can start the barrier.
      // We strongly believe that the MPI standard guarantees
      // if a synchronous send is marked as completed, then there
      // is a corresponding user-posted request for said send.
      // Therefore, send_requests being empty is enough
      // to state that our sends are done and everyone that we have
      // sent data is expecting it. Double therefore, this condition
      // being satisified on all processors in addition to all
      // receive requests being complete is a sufficient stopping
      // criteria
      if (send_requests.empty() && !started_barrier)
        {
          started_barrier = true;
          comm.nonblocking_barrier(barrier_request);
        }

      // There is no data to act on (we reserve a single value in
      // \p incoming for filling within the next poll loop)
      if (incoming.size() == 1)
        // We've started the barrier
        if (started_barrier)
          // The barrier is complete (everyone is done)
          if (barrier_request.test())
            // Profit
            break;
    }

  // There better not be anything left at this point
  timpi_assert(!possibly_receive());

  // Reset the send mode
  const_cast<Communicator &>(comm).send_mode(old_send_mode);

  // So, *did* we see any empty containers being sent?
#ifndef NDEBUG
  empty_send_assertion(comm, empty_target_pid);
#endif // NDEBUG
}

push_parallel_roundrobin_helper()

template<typename MapToContainers , typename SendReceiveFunctor , typename ActionFunctor >

void TIMPI::detail::push_parallel_roundrobin_helper	(	const Communicator &	comm,
		MapToContainers &&	data,
		const SendReceiveFunctor &	sendreceive_functor,
		const ActionFunctor &	act_on_data
	)

Definition at line 568 of file parallel_sync.h.

References empty_send_assertion(), TIMPI::Communicator::get_unique_tag(), TIMPI::Communicator::max(), TIMPI::Communicator::rank(), and TIMPI::Communicator::size().

Referenced by TIMPI::push_parallel_packed_range(), and TIMPI::push_parallel_vector_data().

{
  typedef typename std::remove_reference<MapToContainers>::type::value_type::second_type
    container_type;

  // This function must be run on all processors at once
  timpi_parallel_only(comm);

  // This function implements the simplest protocol possible, fully
  // synchronous.  Every processor talks to every other.  Only use this for
  // debugging, and only when you're desperate.

  unsigned int num_procs = comm.size();

  // Don't give us empty vectors to send.  We'll yell at you (after
  // the sync is done, so all ranks get out of it and we can throw an
  // assertion failure everywhere) if we're debugging and we catch
  // one.
  //
  // But in opt mode we'll just skip empty vectors.
#ifndef NDEBUG
  processor_id_type empty_target_pid = processor_id_type(-1);
#endif

  // Do multiple exchanges if we have an oversized data map
  processor_id_type n_exchanges = 1;
  for (auto & datapair : data)
    {
      const unsigned int dest_pid = datapair.first;
      n_exchanges = std::max(n_exchanges, dest_pid/num_procs+1);

      if (datapair.second.empty())
        {
#ifndef NDEBUG
          empty_target_pid = dest_pid;
#endif
          continue;
        }
    }

  comm.max(n_exchanges);

  // We'll grab a tag so responses and queries won't be confused when
  // this is used within a pull
  auto tag = comm.get_unique_tag();

  // Do the send_receives, blocking
  for (processor_id_type e=0; e != n_exchanges; ++e)
    for (processor_id_type p=0; p != num_procs; ++p)
      {
        const processor_id_type procup =
          cast_int<processor_id_type>((comm.rank() + p) %
                                      num_procs);
        const processor_id_type procdown =
          cast_int<processor_id_type>((comm.rank() + num_procs - p) %
                                      num_procs);

        container_type empty_container;
        auto data_it = data.find(procup + e*num_procs);
        auto * const data_to_send =
          (data_it == data.end()) ?
          &empty_container : &data_it->second;

        container_type received_data;
        sendreceive_functor(procup, *data_to_send,
                            procdown, received_data, tag);

        // Empty containers aren't *real* data, they're an artifact of
        // doing send_receive with everyone.  Just skip them.
        if (!received_data.empty())
          act_on_data(procdown, std::move(received_data));
      }

  // So, *did* we see any empty containers being sent?
#ifndef NDEBUG
  empty_send_assertion(comm, empty_target_pid);
#endif // NDEBUG
}