libstdc++: thread Source File

libstdc++

thread
Go to the documentation of this file.
1// <thread> -*- C++ -*-
2
3// Copyright (C) 2008-2026 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
58namespace 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
298 /// @cond undocumented
299 namespace __detail::__variant
300 {
301 template<typename> struct _Never_valueless_alt; // see <variant>
302
303 // Provide the strong exception-safety guarantee when emplacing a
304 // jthread into a variant.
305 template<>
306 struct _Never_valueless_alt<std::jthread>
307 : true_type
308 { };
309 } // namespace __detail::__variant
310 /// @endcond
311#endif // __cpp_lib_jthread
312
313#ifdef __cpp_lib_formatters // C++ >= 23
314 // We deviate from the standard, that does not put requirements
315 // on _CharT here.
316 template<__format::__char _CharT>
317 requires is_pointer_v<thread::native_handle_type>
318 || is_integral_v<thread::native_handle_type>
319 class formatter<thread::id, _CharT>
320 {
321 public:
322 constexpr typename basic_format_parse_context<_CharT>::iterator
323 parse(basic_format_parse_context<_CharT>& __pc)
324 {
325 __format::_Spec<_CharT> __spec{};
326 __spec._M_align = __format::_Align_right;
327 const auto __last = __pc.end();
328 auto __first = __pc.begin();
329
330 auto __finalize = [this, &__spec] {
331 _M_spec = __spec;
332 };
333
334 auto __finished = [&] {
335 if (__first == __last || *__first == '}')
336 {
337 __finalize();
338 return true;
339 }
340 return false;
341 };
342
343 if (__finished())
344 return __first;
345
346 __first = __spec._M_parse_fill_and_align(__first, __last);
347 if (__finished())
348 return __first;
349
350 __first = __spec._M_parse_width(__first, __last, __pc);
351 if (__finished())
352 return __first;
353
354 std::__throw_format_error("format error: invalid format-spec for "
355 "std::thread::id");
356 }
357
358 template<typename _Out>
359 typename basic_format_context<_Out, _CharT>::iterator
360 format(thread::id __id, basic_format_context<_Out, _CharT>& __fc) const
361 {
362
363 if (__id == thread::id())
364 {
365 const _CharT* __msg;
366 if constexpr (is_same_v<_CharT, char>)
367 __msg = "thread::id of a non-executing thread";
368 else
369 __msg = L"thread::id of a non-executing thread";
370
371 __format::__formatter_str<_CharT> __formatter(_M_spec);
372 return __formatter.format(__msg, __fc);
373 }
374
375 using _HandleFormatter
376 = __conditional_t<is_pointer_v<thread::native_handle_type>,
377 __format::__formatter_ptr<_CharT>,
378 __format::__formatter_int<_CharT>>;
379
380 _HandleFormatter __formatter(_M_spec);
381 return __formatter.format(__id._M_thread, __fc);
382 }
383
384 private:
385 __format::_Spec<_CharT> _M_spec;
386 };
387
388#if __glibcxx_print >= 202406L
389 template<>
390 inline constexpr bool
391 enable_nonlocking_formatter_optimization<thread::id> = true;
392#endif
393
394#endif // __cpp_lib_formatters
395
396 /// @} group threads
397
398_GLIBCXX_END_NAMESPACE_VERSION
399} // namespace
400#endif // C++11
401#endif // _GLIBCXX_THREAD
compare
format
stop_token
c++0x_warning.h
version.h
requires_hosted.h
std_thread.h
this_thread_sleep.h
std::true_type
__bool_constant< true > true_type
The type used as a compile-time boolean with true value.
Definition type_traits:119
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::forward
constexpr _Tp && forward(typename std::remove_reference< _Tp >::type &__t) noexcept
Forward an lvalue.
Definition move.h:72
std
ISO C++ entities toplevel namespace is std.
std::operator<<
std::basic_ostream< _CharT, _Traits > & operator<<(std::basic_ostream< _CharT, _Traits > &__os, const bitset< _Nb > &__x)
Global I/O operators for bitsets.
Definition bitset:1798
std::this_thread::get_id
thread::id get_id() noexcept
The unique identifier of the current thread.
Definition std_thread.h:361
std::basic_ostream
Template class basic_ostream.
Definition ostream.h:72
std::thread
Definition std_thread.h:85
std::thread::id
Definition std_thread.h:99