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multithread_info.cc
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multithread_info.cc
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// ---------------------------------------------------------------------
//
// 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
# define TBB_SUPPRESS_DEPRECATED_MESSAGES 1
# include <tbb/task_scheduler_init.h>
# undef TBB_SUPPRESS_DEPRECATED_MESSAGES
#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