multithread_info.cc

// ---------------------------------------------------------------------
//
// Copyright (C) 2000 - 2019 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE.md at
// the top level directory of deal.II.
//
// ---------------------------------------------------------------------

#include <deal.II/base/multithread_info.h>
#include <deal.II/base/utilities.h>

#ifdef DEAL_II_HAVE_UNISTD_H
#  include <unistd.h>
#endif

#if (defined(__MACH__) && defined(__APPLE__)) || defined(__FreeBSD__)
#  include <sys/sysctl.h>
#  include <sys/types.h>
#endif

#include <algorithm>

#ifdef DEAL_II_WITH_THREADS
#  include <deal.II/base/thread_management.h>

#  include <tbb/task_scheduler_init.h>
#endif

DEAL_II_NAMESPACE_OPEN

#ifdef DEAL_II_WITH_THREADS

/* Detecting how many processors a given machine has is something that
   varies greatly between operating systems. For a few operating
   systems, we have figured out how to do that below, but some others
   are still missing. If you find a way to do this on your favorite
   system, please let us know.
 */


#  if defined(__linux__) || defined(__sun__) || defined(__osf__) || \
    defined(_AIX)

unsigned int
MultithreadInfo::get_n_cpus()
{
  return sysconf(_SC_NPROCESSORS_ONLN);
}

#  elif (defined(__MACH__) && defined(__APPLE__)) || defined(__FreeBSD__)
// This is only tested on a dual G5 2.5GHz running MacOSX 10.3.6
// and on an Intel Mac Book Pro.
// If it doesn't work please contact the mailinglist.
unsigned int
MultithreadInfo::get_n_cpus()
{
  int         mib[2];
  int         n_cpus;
  std::size_t len;

  mib[0] = CTL_HW;
  mib[1] = HW_NCPU;
  len    = sizeof(n_cpus);
  sysctl(mib, 2, &n_cpus, &len, nullptr, 0);

  return n_cpus;
}

#  else

// If you get n_cpus=1 although you are on a multi-processor machine,
// then this may have two reasons: either because the system macros,
// e.g.__linux__, __sgi__, etc. weren't defined by the compiler or the
// detection of processors is really not implemented for your specific
// system. In the first case you can add e.g. -D__sgi__ to your
// compiling flags, in the latter case you need to implement the
// get_n_cpus() function for your system.
//
// In both cases, this #else case is compiled, a fact that you can
// easily verify by uncommenting the following #error directive,
// recompiling and getting a compilation error right at that line.
// After definition of the system macro or the implementation of the
// new detection this #error message during compilation shouldn't
// occur any more.
//
// Please send all new implementations of detection of processors to
// the deal.II mailing list, such that it can be included into the
// next deal.II release.

//#error Detection of Processors not supported on this OS. Setting n_cpus=1 by
// default.

unsigned int
MultithreadInfo::get_n_cpus()
{
  return 1;
}

#  endif

unsigned int
MultithreadInfo::n_cores()
{
  return MultithreadInfo::n_cpus;
}


void
MultithreadInfo::set_thread_limit(const unsigned int max_threads)
{
  // set the maximal number of threads to the given value as specified
  n_max_threads = max_threads;

  // then also see if something was given in the environment
  {
    const char *penv = getenv("DEAL_II_NUM_THREADS");
    if (penv != nullptr)
      {
        unsigned int max_threads_env = numbers::invalid_unsigned_int;
        try
          {
            max_threads_env = Utilities::string_to_int(std::string(penv));
          }
        catch (...)
          {
            AssertThrow(
              false,
              ExcMessage(
                std::string(
                  "When specifying the <DEAL_II_NUM_THREADS> environment "
                  "variable, it needs to be something that can be interpreted "
                  "as an integer. The text you have in the environment "
                  "variable is <") +
                penv + ">"));
          }

        AssertThrow(max_threads_env > 0,
                    ExcMessage(
                      "When specifying the <DEAL_II_NUM_THREADS> environment "
                      "variable, it needs to be a positive number."));

        if (n_max_threads != numbers::invalid_unsigned_int)
          n_max_threads = std::min(n_max_threads, max_threads_env);
        else
          n_max_threads = max_threads_env;
      }
  }
  // Without restrictions from the user query TBB for the recommended number
  // of threads:
  if (n_max_threads == numbers::invalid_unsigned_int)
    n_max_threads = tbb::task_scheduler_init::default_num_threads();

  // Initialize the scheduler and destroy the old one before doing so
  static tbb::task_scheduler_init dummy(tbb::task_scheduler_init::deferred);
  if (dummy.is_active())
    dummy.terminate();
  dummy.initialize(n_max_threads);
}


unsigned int
MultithreadInfo::n_threads()
{
  Assert(n_max_threads != numbers::invalid_unsigned_int, ExcInternalError());
  return n_max_threads;
}


#else // not in MT mode

unsigned int
MultithreadInfo::get_n_cpus()
{
  return 1;
}

unsigned int
MultithreadInfo::n_cores()
{
  return 1;
}

unsigned int
MultithreadInfo::n_threads()
{
  return 1;
}

void
MultithreadInfo::set_thread_limit(const unsigned int)
{}

#endif


bool
MultithreadInfo::is_running_single_threaded()
{
  return n_threads() == 1;
}


std::size_t
MultithreadInfo::memory_consumption()
{
  // only simple data elements, so
  // use sizeof operator
  return sizeof(MultithreadInfo);
}


void
MultithreadInfo::initialize_multithreading()
{
  static bool done = false;
  if (done)
    return;

  MultithreadInfo::set_thread_limit(numbers::invalid_unsigned_int);
  done = true;
}



const unsigned int MultithreadInfo::n_cpus  = MultithreadInfo::get_n_cpus();
unsigned int MultithreadInfo::n_max_threads = numbers::invalid_unsigned_int;

namespace
{
  // Force the first call to set_thread_limit happen before any tasks in TBB are
  // used. This is necessary as tbb::task_scheduler_init has no effect if TBB
  // got automatically initialized (which happens the first time we use it).
  struct DoOnce
  {
    DoOnce()
    {
      MultithreadInfo::initialize_multithreading();
    }
  } do_once;
} // namespace

DEAL_II_NAMESPACE_CLOSE