Reference documentation for deal.II version 9.5.0
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multithread_info.cc
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1// ---------------------------------------------------------------------
2//
3// Copyright (C) 2000 - 2023 by the deal.II authors
4//
5// This file is part of the deal.II library.
6//
7// The deal.II library is free software; you can use it, redistribute
8// it, and/or modify it under the terms of the GNU Lesser General
9// Public License as published by the Free Software Foundation; either
10// version 2.1 of the License, or (at your option) any later version.
11// The full text of the license can be found in the file LICENSE.md at
12// the top level directory of deal.II.
13//
14// ---------------------------------------------------------------------
15
18
19#include <algorithm>
20#include <cstdlib> // for std::getenv
21#include <mutex>
22#include <thread>
23
24#ifdef DEAL_II_WITH_TBB
25# ifdef DEAL_II_TBB_WITH_ONEAPI
26# include <tbb/global_control.h>
27# else
28# include <tbb/task_scheduler_init.h>
29# endif
30#endif
31
32
33#ifdef DEAL_II_WITH_TASKFLOW
34# include <taskflow/taskflow.hpp>
35#endif
36
38
39
40unsigned int
42{
43 // There is a slight semantic change between our n_cores() call and the
44 // std::thread alternative: in case of an error the latter one returns 0
45 // in contrast to a 1 that n_cores() used to do. For compatibility, let's
46 // translate to our numbering scheme:
47 const unsigned int n_cores = std::thread::hardware_concurrency();
48 return n_cores == 0 ? 1 : n_cores;
49}
50
51
52void
53MultithreadInfo::set_thread_limit(const unsigned int max_threads)
54{
55 // set the maximal number of threads to the given value as specified
56 n_max_threads = max_threads;
57
58 // then also see if something was given in the environment
59 {
60 if (const char *penv = std::getenv("DEAL_II_NUM_THREADS"))
61 {
62 unsigned int max_threads_env = numbers::invalid_unsigned_int;
63 try
64 {
65 max_threads_env = Utilities::string_to_int(std::string(penv));
66 }
67 catch (...)
68 {
70 false,
72 std::string(
73 "When specifying the <DEAL_II_NUM_THREADS> environment "
74 "variable, it needs to be something that can be interpreted "
75 "as an integer. The text you have in the environment "
76 "variable is <") +
77 penv + ">"));
78 }
79
80 AssertThrow(max_threads_env > 0,
82 "When specifying the <DEAL_II_NUM_THREADS> environment "
83 "variable, it needs to be a positive number."));
84
86 n_max_threads = std::min(n_max_threads, max_threads_env);
87 else
88 n_max_threads = max_threads_env;
89 }
90 }
91
92 // If we have not set the number of allowed threads yet, just default to
93 // the number of available cores
96
97#ifdef DEAL_II_WITH_TBB
98# ifdef DEAL_II_TBB_WITH_ONEAPI
99 // tbb::global_control is a class that affects the specified behavior of
100 // tbb during its lifetime. Thus, in order to set a global thread limit
101 // for tbb we have to maintain the object throughout the execution of the
102 // program. We do this by maintaining a static std::unique_ptr.
103 //
104 // A std::unique_ptr is a good choice here because tbb::global_control
105 // does not provide a mechanism to override its setting - we can only
106 // delete the old and replace it with a new one.
107 static std::unique_ptr<tbb::global_control> tbb_global_control;
108 tbb_global_control = std::make_unique<tbb::global_control>(
109 tbb::global_control::max_allowed_parallelism, n_max_threads);
110
111# else
112 // Initialize the scheduler and destroy the old one before doing so
113 static tbb::task_scheduler_init dummy(tbb::task_scheduler_init::deferred);
114 if (dummy.is_active())
115 dummy.terminate();
116 dummy.initialize(n_max_threads);
117# endif
118#endif
119
120#ifdef DEAL_II_WITH_TASKFLOW
121 executor = std::make_unique<tf::Executor>(n_max_threads);
122#endif
123}
124
125
126
127unsigned int
129{
131 return n_max_threads;
132}
133
134
135
136bool
138{
139 return n_threads() == 1;
140}
141
142
143
144std::size_t
146{
147 // only simple data elements, so use sizeof operator
148 return sizeof(MultithreadInfo);
149}
150
151
152
153void
155{
156 static std::once_flag is_initialized;
157 std::call_once(is_initialized, []() {
159 });
160}
161
162
163
164#ifdef DEAL_II_WITH_TASKFLOW
165tf::Executor &
167{
168 // This should not trigger in normal user code, because we initialize the
169 // Executor in the static DoOnce struct at the end of this file unless you
170 // ask for the Executor before this static object gets constructed.
171 Assert(
172 executor.get() != nullptr,
174 "Please initialize multithreading using MultithreadInfo::set_thread_limit() first."));
175 return *(executor.get());
176}
177
178std::unique_ptr<tf::Executor> MultithreadInfo::executor = nullptr;
179#endif
180
182
183namespace
184{
185 // Force the first call to set_thread_limit happen before any tasks in TBB are
186 // used. This is necessary as tbb::task_scheduler_init has no effect if TBB
187 // got automatically initialized (which happens the first time we use it).
188 struct DoOnce
189 {
190 DoOnce()
191 {
193 }
194 } do_once;
195} // namespace
196
static unsigned int n_max_threads
MultithreadInfo()=delete
static bool is_running_single_threaded()
static std::unique_ptr< tf::Executor > executor
static void initialize_multithreading()
static unsigned int n_cores()
static unsigned int n_threads()
static void set_thread_limit(const unsigned int max_threads=numbers::invalid_unsigned_int)
static std::size_t memory_consumption()
static tf::Executor & get_taskflow_executor()
#define DEAL_II_NAMESPACE_OPEN
Definition config.h:472
#define DEAL_II_NAMESPACE_CLOSE
Definition config.h:473
#define Assert(cond, exc)
static ::ExceptionBase & ExcInternalError()
static ::ExceptionBase & ExcMessage(std::string arg1)
#define AssertThrow(cond, exc)
int string_to_int(const std::string &s)
Definition utilities.cc:606
static const unsigned int invalid_unsigned_int
Definition types.h:213
::VectorizedArray< Number, width > min(const ::VectorizedArray< Number, width > &, const ::VectorizedArray< Number, width > &)