libstdc++
thread
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1 // <thread> -*- C++ -*-
2 
3 // Copyright (C) 2008-2024 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 #include <bits/requires_hosted.h> // concurrency
35 
36 #if __cplusplus < 201103L
37 # include <bits/c++0x_warning.h>
38 #else
39 
40 #if __cplusplus > 201703L
41 # include <compare> // std::strong_ordering
42 # include <stop_token> // std::stop_source, std::stop_token, std::nostopstate
43 #endif
44 
45 #include <bits/std_thread.h> // std::thread, get_id, yield
46 #include <bits/this_thread_sleep.h> // std::this_thread::sleep_for, sleep_until
47 
48 #define __glibcxx_want_jthread
49 #define __glibcxx_want_formatters
50 #include <bits/version.h>
51 
52 #if __cpp_lib_formatters
53 # include <format>
54 #endif
55 
56 namespace std _GLIBCXX_VISIBILITY(default)
57 {
58 _GLIBCXX_BEGIN_NAMESPACE_VERSION
59 
60  /**
61  * @defgroup threads Threads
62  * @ingroup concurrency
63  * @since C++11
64  *
65  * Classes for thread support.
66  * @{
67  */
68 
69  // std::thread is defined in <bits/std_thread.h>
70 
71  /// @relates std::thread::id @{
72 
73 #if __cpp_lib_three_way_comparison
74  inline strong_ordering
75  operator<=>(thread::id __x, thread::id __y) noexcept
76  { return __x._M_thread <=> __y._M_thread; }
77 #else
78  inline bool
79  operator!=(thread::id __x, thread::id __y) noexcept
80  { return !(__x == __y); }
81 
82  inline bool
83  operator<(thread::id __x, thread::id __y) noexcept
84  {
85  // Pthreads doesn't define any way to do this, so we just have to
86  // assume native_handle_type is LessThanComparable.
87  return __x._M_thread < __y._M_thread;
88  }
89 
90  inline bool
91  operator<=(thread::id __x, thread::id __y) noexcept
92  { return !(__y < __x); }
93 
94  inline bool
95  operator>(thread::id __x, thread::id __y) noexcept
96  { return __y < __x; }
97 
98  inline bool
99  operator>=(thread::id __x, thread::id __y) noexcept
100  { return !(__x < __y); }
101 #endif // __cpp_lib_three_way_comparison
102 
103  template<class _CharT, class _Traits>
104  inline basic_ostream<_CharT, _Traits>&
105  operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
106  {
107  // Convert non-void pointers to const void* for formatted output.
108  using __output_type
109  = __conditional_t<is_pointer<thread::native_handle_type>::value,
110  const void*,
111  thread::native_handle_type>;
112 
113  if (__id == thread::id())
114  return __out << "thread::id of a non-executing thread";
115  else
116  return __out << static_cast<__output_type>(__id._M_thread);
117  }
118  /// @}
119 
120 #ifdef __cpp_lib_jthread // C++ >= 20
121 
122  /// @cond undocumented
123 #ifndef __STRICT_ANSI__
124  template<typename _Callable, typename... _Args>
125  constexpr bool __pmf_expects_stop_token = false;
126 
127  template<typename _Callable, typename _Obj, typename... _Args>
128  constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...>
129  = __and_<is_member_function_pointer<remove_reference_t<_Callable>>,
130  is_invocable<_Callable, _Obj, stop_token, _Args...>>::value;
131 #endif
132  /// @endcond
133 
134  /** A thread with cancellation and automatic joining.
135  *
136  * Unlike `std::thread`, destroying a joinable `std::jthread` will not
137  * terminate the process. Instead, it will try to request its thread to
138  * stop, then will join it.
139  *
140  * A `std::jthread` has a `std::stop_source` member which will be passed
141  * as the first argument to the callable that runs in the new thread
142  * (as long as the callable will accept that argument). That can then
143  * be used to send a stop request that the new thread can test for.
144  *
145  * @headerfile thread
146  * @since C++20
147  */
148  class jthread
149  {
150  public:
151  using id = thread::id;
152  using native_handle_type = thread::native_handle_type;
153 
154  jthread() noexcept
155  : _M_stop_source{nostopstate}
156  { }
157 
158  template<typename _Callable, typename... _Args,
159  typename = enable_if_t<!is_same_v<remove_cvref_t<_Callable>,
160  jthread>>>
161  explicit
162  jthread(_Callable&& __f, _Args&&... __args)
163  : _M_thread{_S_create(_M_stop_source, std::forward<_Callable>(__f),
164  std::forward<_Args>(__args)...)}
165  { }
166 
167  jthread(const jthread&) = delete;
168  jthread(jthread&&) noexcept = default;
169 
170  ~jthread()
171  {
172  if (joinable())
173  {
174  request_stop();
175  join();
176  }
177  }
178 
179  jthread&
180  operator=(const jthread&) = delete;
181 
182  jthread&
183  operator=(jthread&& __other) noexcept
184  {
185  std::jthread(std::move(__other)).swap(*this);
186  return *this;
187  }
188 
189  void
190  swap(jthread& __other) noexcept
191  {
192  std::swap(_M_stop_source, __other._M_stop_source);
193  std::swap(_M_thread, __other._M_thread);
194  }
195 
196  [[nodiscard]] bool
197  joinable() const noexcept
198  {
199  return _M_thread.joinable();
200  }
201 
202  void
203  join()
204  {
205  _M_thread.join();
206  }
207 
208  void
209  detach()
210  {
211  _M_thread.detach();
212  }
213 
214  [[nodiscard]] id
215  get_id() const noexcept
216  {
217  return _M_thread.get_id();
218  }
219 
220  [[nodiscard]] native_handle_type
221  native_handle()
222  {
223  return _M_thread.native_handle();
224  }
225 
226  [[nodiscard]] static unsigned
227  hardware_concurrency() noexcept
228  {
229  return thread::hardware_concurrency();
230  }
231 
232  [[nodiscard]] stop_source
233  get_stop_source() noexcept
234  {
235  return _M_stop_source;
236  }
237 
238  [[nodiscard]] stop_token
239  get_stop_token() const noexcept
240  {
241  return _M_stop_source.get_token();
242  }
243 
244  bool request_stop() noexcept
245  {
246  return _M_stop_source.request_stop();
247  }
248 
249  friend void swap(jthread& __lhs, jthread& __rhs) noexcept
250  {
251  __lhs.swap(__rhs);
252  }
253 
254  private:
255  template<typename _Callable, typename... _Args>
256  static thread
257  _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args)
258  {
259 #ifndef __STRICT_ANSI__
260  if constexpr (__pmf_expects_stop_token<_Callable, _Args...>)
261  return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...);
262  else
263 #endif
264  if constexpr(is_invocable_v<decay_t<_Callable>, stop_token,
265  decay_t<_Args>...>)
266  return thread{std::forward<_Callable>(__f), __ssrc.get_token(),
267  std::forward<_Args>(__args)...};
268  else
269  {
270  static_assert(is_invocable_v<decay_t<_Callable>,
271  decay_t<_Args>...>,
272  "std::jthread arguments must be invocable after"
273  " conversion to rvalues");
274  return thread{std::forward<_Callable>(__f),
275  std::forward<_Args>(__args)...};
276  }
277  }
278 
279 #ifndef __STRICT_ANSI__
280  template<typename _Callable, typename _Obj, typename... _Args>
281  static thread
282  _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj,
283  _Args&&... __args)
284  {
285  return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(),
286  std::forward<_Args>(__args)...};
287  }
288 #endif
289 
290  stop_source _M_stop_source;
291  thread _M_thread;
292  };
293 #endif // __cpp_lib_jthread
294 
295 #ifdef __cpp_lib_formatters // C++ >= 23
296  template<typename _CharT>
297  requires is_pointer_v<thread::native_handle_type>
298  || is_integral_v<thread::native_handle_type>
299  class formatter<thread::id, _CharT>
300  {
301  public:
302  constexpr typename basic_format_parse_context<_CharT>::iterator
303  parse(basic_format_parse_context<_CharT>& __pc)
304  {
305  __format::_Spec<_CharT> __spec{};
306  const auto __last = __pc.end();
307  auto __first = __pc.begin();
308 
309  auto __finalize = [this, &__spec] {
310  _M_spec = __spec;
311  };
312 
313  auto __finished = [&] {
314  if (__first == __last || *__first == '}')
315  {
316  __finalize();
317  return true;
318  }
319  return false;
320  };
321 
322  if (__finished())
323  return __first;
324 
325  __first = __spec._M_parse_fill_and_align(__first, __last);
326  if (__finished())
327  return __first;
328 
329  __first = __spec._M_parse_width(__first, __last, __pc);
330  if (__finished())
331  return __first;
332 
333  __throw_format_error("format error: invalid format-spec for "
334  "std::thread::id");
335  }
336 
337  template<typename _Out>
338  typename basic_format_context<_Out, _CharT>::iterator
339  format(thread::id __id, basic_format_context<_Out, _CharT>& __fc) const
340  {
341  basic_string_view<_CharT> __sv;
342  if constexpr (is_same_v<_CharT, char>)
343  __sv = "{}thread::id of a non-executing thread";
344  else
345  __sv = L"{}thread::id of a non-executing thread";
346  basic_string<_CharT> __str;
347  if (__id == thread::id())
348  __sv.remove_prefix(2);
349  else
350  {
351  using _FmtStr = __format::_Runtime_format_string<_CharT>;
352  // Convert non-void pointers to const void* for formatted output.
353  using __output_type
354  = __conditional_t<is_pointer_v<thread::native_handle_type>,
355  const void*,
356  thread::native_handle_type>;
357  auto __o = static_cast<__output_type>(__id._M_thread);
358  __sv = __str = std::format(_FmtStr(__sv.substr(0, 2)), __o);
359  }
360  return __format::__write_padded_as_spec(__sv, __sv.size(),
361  __fc, _M_spec,
362  __format::_Align_right);
363  }
364 
365  private:
366  __format::_Spec<_CharT> _M_spec;
367  };
368 #endif // __cpp_lib_formatters
369 
370  /// @} group threads
371 
372 _GLIBCXX_END_NAMESPACE_VERSION
373 } // namespace
374 #endif // C++11
375 #endif // _GLIBCXX_THREAD