libstdc++
thread
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1 // <thread> -*- C++ -*-
2 
3 // Copyright (C) 2008-2022 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /** @file include/thread
26  * This is a Standard C++ Library header.
27  */
28 
29 #ifndef _GLIBCXX_THREAD
30 #define _GLIBCXX_THREAD 1
31 
32 #pragma GCC system_header
33 
34 #if __cplusplus < 201103L
35 # include <bits/c++0x_warning.h>
36 #else
37 
38 #if __cplusplus > 201703L
39 # include <compare> // std::strong_ordering
40 # include <stop_token> // std::stop_source, std::stop_token, std::nostopstate
41 #endif
42 
43 #include <bits/std_thread.h> // std::thread, get_id, yield
44 #include <bits/this_thread_sleep.h> // std::this_thread::sleep_for, sleep_until
45 
46 namespace std _GLIBCXX_VISIBILITY(default)
47 {
48 _GLIBCXX_BEGIN_NAMESPACE_VERSION
49 
50  /**
51  * @defgroup threads Threads
52  * @ingroup concurrency
53  * @since C++11
54  *
55  * Classes for thread support.
56  * @{
57  */
58 
59  // std::thread is defined in <bits/std_thread.h>
60 
61  /// @relates std::thread::id @{
62 
63 #if __cpp_lib_three_way_comparison
64  inline strong_ordering
65  operator<=>(thread::id __x, thread::id __y) noexcept
66  { return __x._M_thread <=> __y._M_thread; }
67 #else
68  inline bool
69  operator!=(thread::id __x, thread::id __y) noexcept
70  { return !(__x == __y); }
71 
72  inline bool
73  operator<(thread::id __x, thread::id __y) noexcept
74  {
75  // Pthreads doesn't define any way to do this, so we just have to
76  // assume native_handle_type is LessThanComparable.
77  return __x._M_thread < __y._M_thread;
78  }
79 
80  inline bool
81  operator<=(thread::id __x, thread::id __y) noexcept
82  { return !(__y < __x); }
83 
84  inline bool
85  operator>(thread::id __x, thread::id __y) noexcept
86  { return __y < __x; }
87 
88  inline bool
89  operator>=(thread::id __x, thread::id __y) noexcept
90  { return !(__x < __y); }
91 #endif // __cpp_lib_three_way_comparison
92 
93  template<class _CharT, class _Traits>
94  inline basic_ostream<_CharT, _Traits>&
95  operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
96  {
97  if (__id == thread::id())
98  return __out << "thread::id of a non-executing thread";
99  else
100  return __out << __id._M_thread;
101  }
102  /// @}
103 
104 #ifdef __cpp_lib_jthread
105 
106  /// @cond undocumented
107 #ifndef __STRICT_ANSI__
108  template<typename _Callable, typename... _Args>
109  constexpr bool __pmf_expects_stop_token = false;
110 
111  template<typename _Callable, typename _Obj, typename... _Args>
112  constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...>
113  = __and_<is_member_function_pointer<remove_reference_t<_Callable>>,
114  is_invocable<_Callable, _Obj, stop_token, _Args...>>::value;
115 #endif
116  /// @endcond
117 
118  /** A thread with cancellation and automatic joining.
119  *
120  * Unlike `std::thread`, destroying a joinable `std::jthread` will not
121  * terminate the process. Instead, it will try to request its thread to
122  * stop, then will join it.
123  *
124  * A `std::jthread` has a `std::stop_source` member which will be passed
125  * as the first argument to the callable that runs in the new thread
126  * (as long as the callable will accept that argument). That can then
127  * be used to send a stop request that the new thread can test for.
128  *
129  * @headerfile thread
130  * @since C++20
131  */
132  class jthread
133  {
134  public:
135  using id = thread::id;
136  using native_handle_type = thread::native_handle_type;
137 
138  jthread() noexcept
139  : _M_stop_source{nostopstate}
140  { }
141 
142  template<typename _Callable, typename... _Args,
144  jthread>>>
145  explicit
146  jthread(_Callable&& __f, _Args&&... __args)
147  : _M_thread{_S_create(_M_stop_source, std::forward<_Callable>(__f),
148  std::forward<_Args>(__args)...)}
149  { }
150 
151  jthread(const jthread&) = delete;
152  jthread(jthread&&) noexcept = default;
153 
154  ~jthread()
155  {
156  if (joinable())
157  {
158  request_stop();
159  join();
160  }
161  }
162 
163  jthread&
164  operator=(const jthread&) = delete;
165 
166  jthread&
167  operator=(jthread&& __other) noexcept
168  {
169  std::jthread(std::move(__other)).swap(*this);
170  return *this;
171  }
172 
173  void
174  swap(jthread& __other) noexcept
175  {
176  std::swap(_M_stop_source, __other._M_stop_source);
177  std::swap(_M_thread, __other._M_thread);
178  }
179 
180  [[nodiscard]] bool
181  joinable() const noexcept
182  {
183  return _M_thread.joinable();
184  }
185 
186  void
187  join()
188  {
189  _M_thread.join();
190  }
191 
192  void
193  detach()
194  {
195  _M_thread.detach();
196  }
197 
198  [[nodiscard]] id
199  get_id() const noexcept
200  {
201  return _M_thread.get_id();
202  }
203 
204  [[nodiscard]] native_handle_type
205  native_handle()
206  {
207  return _M_thread.native_handle();
208  }
209 
210  [[nodiscard]] static unsigned
211  hardware_concurrency() noexcept
212  {
213  return thread::hardware_concurrency();
214  }
215 
216  [[nodiscard]] stop_source
217  get_stop_source() noexcept
218  {
219  return _M_stop_source;
220  }
221 
222  [[nodiscard]] stop_token
223  get_stop_token() const noexcept
224  {
225  return _M_stop_source.get_token();
226  }
227 
228  bool request_stop() noexcept
229  {
230  return _M_stop_source.request_stop();
231  }
232 
233  friend void swap(jthread& __lhs, jthread& __rhs) noexcept
234  {
235  __lhs.swap(__rhs);
236  }
237 
238  private:
239  template<typename _Callable, typename... _Args>
240  static thread
241  _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args)
242  {
243 #ifndef __STRICT_ANSI__
244  if constexpr (__pmf_expects_stop_token<_Callable, _Args...>)
245  return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...);
246  else
247 #endif
248  if constexpr(is_invocable_v<decay_t<_Callable>, stop_token,
249  decay_t<_Args>...>)
250  return thread{std::forward<_Callable>(__f), __ssrc.get_token(),
251  std::forward<_Args>(__args)...};
252  else
253  {
254  static_assert(is_invocable_v<decay_t<_Callable>,
255  decay_t<_Args>...>,
256  "std::jthread arguments must be invocable after"
257  " conversion to rvalues");
258  return thread{std::forward<_Callable>(__f),
259  std::forward<_Args>(__args)...};
260  }
261  }
262 
263 #ifndef __STRICT_ANSI__
264  template<typename _Callable, typename _Obj, typename... _Args>
265  static thread
266  _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj,
267  _Args&&... __args)
268  {
269  return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(),
270  std::forward<_Args>(__args)...};
271  }
272 #endif
273 
274  stop_source _M_stop_source;
275  thread _M_thread;
276  };
277 #endif // __cpp_lib_jthread
278 
279  /// @} group threads
280 
281 _GLIBCXX_END_NAMESPACE_VERSION
282 } // namespace
283 #endif // C++11
284 #endif // _GLIBCXX_THREAD
typename decay< _Tp >::type decay_t
Alias template for decay.
Definition: type_traits:2604
typename enable_if< _Cond, _Tp >::type enable_if_t
Alias template for enable_if.
Definition: type_traits:2608
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
void swap(any &__x, any &__y) noexcept
Exchange the states of two any objects.
Definition: any:429
ISO C++ entities toplevel namespace is std.
std::basic_ostream< _CharT, _Traits > & operator<<(std::basic_ostream< _CharT, _Traits > &__os, const bitset< _Nb > &__x)
Global I/O operators for bitsets.
Definition: bitset:1543
Allow testing whether a stop request has been made on a stop_source.
Definition: stop_token:53
A type that allows a stop request to be made.
Definition: stop_token:479
native_handle_type native_handle()
Definition: std_thread.h:211