libstdc++
thread
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1 // <thread> -*- C++ -*-
2 
3 // Copyright (C) 2008-2025 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 #ifdef _GLIBCXX_SYSHDR
33 #pragma GCC system_header
34 #endif
35 
36 #include <bits/requires_hosted.h> // concurrency
37 
38 #if __cplusplus < 201103L
39 # include <bits/c++0x_warning.h>
40 #else
41 
42 #if __cplusplus > 201703L
43 # include <compare> // std::strong_ordering
44 # include <stop_token> // std::stop_source, std::stop_token, std::nostopstate
45 #endif
46 
47 #include <bits/std_thread.h> // std::thread, get_id, yield
48 #include <bits/this_thread_sleep.h> // std::this_thread::sleep_for, sleep_until
49 
50 #define __glibcxx_want_jthread
51 #define __glibcxx_want_formatters
52 #include <bits/version.h>
53 
54 #if __cpp_lib_formatters
55 # include <format>
56 #endif
57 
58 namespace std _GLIBCXX_VISIBILITY(default)
59 {
60 _GLIBCXX_BEGIN_NAMESPACE_VERSION
61 
62  /**
63  * @defgroup threads Threads
64  * @ingroup concurrency
65  * @since C++11
66  *
67  * Classes for thread support.
68  * @{
69  */
70 
71  // std::thread is defined in <bits/std_thread.h>
72 
73  /// @relates std::thread::id @{
74 
75 #if __cpp_lib_three_way_comparison
76  inline strong_ordering
77  operator<=>(thread::id __x, thread::id __y) noexcept
78  { return __x._M_thread <=> __y._M_thread; }
79 #else
80  inline bool
81  operator!=(thread::id __x, thread::id __y) noexcept
82  { return !(__x == __y); }
83 
84  inline bool
85  operator<(thread::id __x, thread::id __y) noexcept
86  {
87  // Pthreads doesn't define any way to do this, so we just have to
88  // assume native_handle_type is LessThanComparable.
89  return __x._M_thread < __y._M_thread;
90  }
91 
92  inline bool
93  operator<=(thread::id __x, thread::id __y) noexcept
94  { return !(__y < __x); }
95 
96  inline bool
97  operator>(thread::id __x, thread::id __y) noexcept
98  { return __y < __x; }
99 
100  inline bool
101  operator>=(thread::id __x, thread::id __y) noexcept
102  { return !(__x < __y); }
103 #endif // __cpp_lib_three_way_comparison
104 
105  template<class _CharT, class _Traits>
106  inline basic_ostream<_CharT, _Traits>&
107  operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
108  {
109  // Convert non-void pointers to const void* for formatted output.
110  using __output_type
111  = __conditional_t<is_pointer<thread::native_handle_type>::value,
112  const void*,
113  thread::native_handle_type>;
114 
115  if (__id == thread::id())
116  return __out << "thread::id of a non-executing thread";
117  else
118  return __out << static_cast<__output_type>(__id._M_thread);
119  }
120  /// @}
121 
122 #ifdef __cpp_lib_jthread // C++ >= 20
123 
124  /// @cond undocumented
125 #ifndef __STRICT_ANSI__
126  // As an extension we support invoking a pointer-to-member-function that
127  // expects a stop_token as the first argument. See PR libstdc++/100612.
128  template<typename _Callable, typename... _Args>
129  constexpr bool __pmf_expects_stop_token = false;
130 
131  template<typename _Callable, typename _Obj, typename... _Args>
132  requires is_member_function_pointer_v<remove_reference_t<_Callable>>
133  constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...>
134  = is_invocable_v<_Callable, _Obj, stop_token, _Args...>;
135 #endif
136  /// @endcond
137 
138  /** A thread with cancellation and automatic joining.
139  *
140  * Unlike `std::thread`, destroying a joinable `std::jthread` will not
141  * terminate the process. Instead, it will try to request its thread to
142  * stop, then will join it.
143  *
144  * A `std::jthread` has a `std::stop_source` member which will be passed
145  * as the first argument to the callable that runs in the new thread
146  * (as long as the callable will accept that argument). That can then
147  * be used to send a stop request that the new thread can test for.
148  *
149  * @headerfile thread
150  * @since C++20
151  */
152  class jthread
153  {
154  public:
155  using id = thread::id;
156  using native_handle_type = thread::native_handle_type;
157 
158  jthread() noexcept
159  : _M_stop_source{nostopstate}
160  { }
161 
162  template<typename _Callable, typename... _Args,
163  typename = enable_if_t<!is_same_v<remove_cvref_t<_Callable>,
164  jthread>>>
165  explicit
166  jthread(_Callable&& __f, _Args&&... __args)
167  : _M_thread{_S_create(_M_stop_source, std::forward<_Callable>(__f),
168  std::forward<_Args>(__args)...)}
169  { }
170 
171  jthread(const jthread&) = delete;
172  jthread(jthread&&) noexcept = default;
173 
174  ~jthread()
175  {
176  if (joinable())
177  {
178  request_stop();
179  join();
180  }
181  }
182 
183  jthread&
184  operator=(const jthread&) = delete;
185 
186  jthread&
187  operator=(jthread&& __other) noexcept
188  {
189  std::jthread(std::move(__other)).swap(*this);
190  return *this;
191  }
192 
193  void
194  swap(jthread& __other) noexcept
195  {
196  std::swap(_M_stop_source, __other._M_stop_source);
197  std::swap(_M_thread, __other._M_thread);
198  }
199 
200  [[nodiscard]] bool
201  joinable() const noexcept
202  {
203  return _M_thread.joinable();
204  }
205 
206  void
207  join()
208  {
209  _M_thread.join();
210  }
211 
212  void
213  detach()
214  {
215  _M_thread.detach();
216  }
217 
218  [[nodiscard]] id
219  get_id() const noexcept
220  {
221  return _M_thread.get_id();
222  }
223 
224  [[nodiscard]] native_handle_type
225  native_handle()
226  {
227  return _M_thread.native_handle();
228  }
229 
230  [[nodiscard]] static unsigned
231  hardware_concurrency() noexcept
232  {
233  return thread::hardware_concurrency();
234  }
235 
236  [[nodiscard]] stop_source
237  get_stop_source() noexcept
238  {
239  return _M_stop_source;
240  }
241 
242  [[nodiscard]] stop_token
243  get_stop_token() const noexcept
244  {
245  return _M_stop_source.get_token();
246  }
247 
248  bool request_stop() noexcept
249  {
250  return _M_stop_source.request_stop();
251  }
252 
253  friend void swap(jthread& __lhs, jthread& __rhs) noexcept
254  {
255  __lhs.swap(__rhs);
256  }
257 
258  private:
259  template<typename _Callable, typename... _Args>
260  static thread
261  _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args)
262  {
263 #ifndef __STRICT_ANSI__
264  if constexpr (__pmf_expects_stop_token<_Callable, _Args...>)
265  return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...);
266  else
267 #endif
268  if constexpr(is_invocable_v<decay_t<_Callable>, stop_token,
269  decay_t<_Args>...>)
270  return thread{std::forward<_Callable>(__f), __ssrc.get_token(),
271  std::forward<_Args>(__args)...};
272  else
273  {
274  static_assert(is_invocable_v<decay_t<_Callable>,
275  decay_t<_Args>...>,
276  "std::jthread arguments must be invocable after"
277  " conversion to rvalues");
278  return thread{std::forward<_Callable>(__f),
279  std::forward<_Args>(__args)...};
280  }
281  }
282 
283 #ifndef __STRICT_ANSI__
284  template<typename _Callable, typename _Obj, typename... _Args>
285  static thread
286  _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj,
287  _Args&&... __args)
288  {
289  return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(),
290  std::forward<_Args>(__args)...};
291  }
292 #endif
293 
294  stop_source _M_stop_source;
295  thread _M_thread;
296  };
297 #endif // __cpp_lib_jthread
298 
299 #ifdef __cpp_lib_formatters // C++ >= 23
300  template<typename _CharT>
301  requires is_pointer_v<thread::native_handle_type>
302  || is_integral_v<thread::native_handle_type>
303  class formatter<thread::id, _CharT>
304  {
305  public:
306  constexpr typename basic_format_parse_context<_CharT>::iterator
307  parse(basic_format_parse_context<_CharT>& __pc)
308  {
309  __format::_Spec<_CharT> __spec{};
310  const auto __last = __pc.end();
311  auto __first = __pc.begin();
312 
313  auto __finalize = [this, &__spec] {
314  _M_spec = __spec;
315  };
316 
317  auto __finished = [&] {
318  if (__first == __last || *__first == '}')
319  {
320  __finalize();
321  return true;
322  }
323  return false;
324  };
325 
326  if (__finished())
327  return __first;
328 
329  __first = __spec._M_parse_fill_and_align(__first, __last);
330  if (__finished())
331  return __first;
332 
333  __first = __spec._M_parse_width(__first, __last, __pc);
334  if (__finished())
335  return __first;
336 
337  __throw_format_error("format error: invalid format-spec for "
338  "std::thread::id");
339  }
340 
341  template<typename _Out>
342  typename basic_format_context<_Out, _CharT>::iterator
343  format(thread::id __id, basic_format_context<_Out, _CharT>& __fc) const
344  {
345  basic_string_view<_CharT> __sv;
346  if constexpr (is_same_v<_CharT, char>)
347  __sv = "{}thread::id of a non-executing thread";
348  else
349  __sv = L"{}thread::id of a non-executing thread";
350  basic_string<_CharT> __str;
351  if (__id == thread::id())
352  __sv.remove_prefix(2);
353  else
354  {
355  using _FmtStr = __format::_Runtime_format_string<_CharT>;
356  // Convert non-void pointers to const void* for formatted output.
357  using __output_type
358  = __conditional_t<is_pointer_v<thread::native_handle_type>,
359  const void*,
360  thread::native_handle_type>;
361  auto __o = static_cast<__output_type>(__id._M_thread);
362  __sv = __str = std::format(_FmtStr(__sv.substr(0, 2)), __o);
363  }
364  return __format::__write_padded_as_spec(__sv, __sv.size(),
365  __fc, _M_spec,
366  __format::_Align_right);
367  }
368 
369  private:
370  __format::_Spec<_CharT> _M_spec;
371  };
372 #endif // __cpp_lib_formatters
373 
374  /// @} group threads
375 
376 _GLIBCXX_END_NAMESPACE_VERSION
377 } // namespace
378 #endif // C++11
379 #endif // _GLIBCXX_THREAD