libstdc++: std_thread.h Source File

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std_thread.h
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1// std::thread declarations -*- 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 bits/std_thread.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{thread}
28 */
29
30#ifndef _GLIBCXX_THREAD_H
31#define _GLIBCXX_THREAD_H 1
32
33#ifdef _GLIBCXX_SYSHDR
34#pragma GCC system_header
35#endif
36
37#if __cplusplus >= 201103L
38#include <bits/c++config.h>
39
40#include <bits/iosfwd.h> // std::basic_ostream
41#include <tuple> // std::tuple
42#include <bits/functional_hash.h> // std::hash
43#include <bits/invoke.h> // std::__invoke
44#include <bits/refwrap.h> // not required, but helpful to users
45#include <bits/unique_ptr.h> // std::unique_ptr
46
47#ifdef _GLIBCXX_HAS_GTHREADS
48# include <bits/gthr.h>
49#else
50# include <errno.h>
51# include <bits/functexcept.h>
52#endif
53
54namespace std _GLIBCXX_VISIBILITY(default)
55{
56_GLIBCXX_BEGIN_NAMESPACE_VERSION
57
58#if __glibcxx_formatters
59 template<typename, typename> class formatter;
60#endif
61
62 /** @addtogroup threads
63 * @{
64 */
65
66 /** A std::thread represents a new thread of execution.
67 *
68 * The default constructor creates an object that does not own a thread.
69 * The `thread(F&&, Args&&...)` constructor invokes a callable in a new
70 * thread, and owns that new thread. A `std::thread` that owns a thread
71 * is *joinable*. Joining a thread waits for it to finish executing,
72 * which happens when the callable running in that thread returns.
73 *
74 * A `std::thread` cannot be copied, but can be moved. Moving a joinable
75 * object transfers ownership of its thread to another object.
76 *
77 * A joinable `std::thread` must be explicitly joined (or detached) before
78 * it is destroyed or assigned to. Attempting to destroy a joinable thread
79 * will terminate the whole process.
80 *
81 * @headerfile thread
82 * @since C++11
83 */
84 class thread
85 {
86 public:
87#ifdef _GLIBCXX_HAS_GTHREADS
88 using native_handle_type = __gthread_t;
89#else
90 using native_handle_type = int;
91#endif
92
93 /** A std::thread::id is a unique identifier for a thread.
94 *
95 * @headerfile thread
96 * @since C++11
97 */
98 class id
99 {
100 native_handle_type _M_thread;
101
102 public:
103 id() noexcept : _M_thread() { }
104
105 explicit
106 id(native_handle_type __id) : _M_thread(__id) { }
107
108 private:
109 friend class thread;
110 friend struct hash<id>;
111
112 friend bool
113 operator==(id __x, id __y) noexcept;
114
115#if __cpp_lib_three_way_comparison
116 friend strong_ordering
117 operator<=>(id __x, id __y) noexcept;
118#else
119 friend bool
120 operator<(id __x, id __y) noexcept;
121#endif
122
123 template<class _CharT, class _Traits>
124 friend basic_ostream<_CharT, _Traits>&
125 operator<<(basic_ostream<_CharT, _Traits>& __out, id __id);
126
127#if __glibcxx_formatters
128 friend formatter<id, char>;
129 friend formatter<id, wchar_t>;
130#endif
131 };
132
133 private:
134 id _M_id;
135
136 // _GLIBCXX_RESOLVE_LIB_DEFECTS
137 // 2097. packaged_task constructors should be constrained
138 // 3039. Unnecessary decay in thread and packaged_task
139 template<typename _Tp>
140 using __not_same = __not_<is_same<__remove_cvref_t<_Tp>, thread>>;
141
142 public:
143 thread() noexcept = default;
144
145#ifdef _GLIBCXX_HAS_GTHREADS
146 private:
147 // This adds to user code that creates std:thread objects (because
148 // it is called by the template ctor below) strong references to
149 // pthread_create and pthread_join, which ensures they are both
150 // linked in even during static linking. We can't depend on
151 // gthread calls to bring them in, because those may use weak
152 // references.
153 static void
154 _M_thread_deps_never_run() {
155#ifdef GTHR_ACTIVE_PROXY
156 reinterpret_cast<void (*)(void)>(&pthread_create)();
157 reinterpret_cast<void (*)(void)>(&pthread_join)();
158#endif
159 }
160
161 public:
162 template<typename _Callable, typename... _Args,
163 typename = _Require<__not_same<_Callable>>>
164 explicit
165 thread(_Callable&& __f, _Args&&... __args)
166 {
167 static_assert( __is_invocable<typename decay<_Callable>::type,
168 typename decay<_Args>::type...>::value,
169 "std::thread arguments must be invocable after conversion to rvalues"
170 );
171
172 using _Wrapper = _Call_wrapper<_Callable, _Args...>;
173 // Create a call wrapper with DECAY_COPY(__f) as its target object
174 // and DECAY_COPY(__args)... as its bound argument entities.
175 _M_start_thread(_State_ptr(new _State_impl<_Wrapper>(
176 std::forward<_Callable>(__f), std::forward<_Args>(__args)...)),
177 _M_thread_deps_never_run);
178 }
179#endif // _GLIBCXX_HAS_GTHREADS
180
181 ~thread()
182 {
183 if (joinable())
184 std::__terminate();
185 }
186
187 thread(const thread&) = delete;
188
189 thread(thread&& __t) noexcept
190 { swap(__t); }
191
192 thread& operator=(const thread&) = delete;
193
194 thread& operator=(thread&& __t) noexcept
195 {
196 if (joinable())
197 std::__terminate();
198 swap(__t);
199 return *this;
200 }
201
202 void
203 swap(thread& __t) noexcept
204 { std::swap(_M_id, __t._M_id); }
205
206 bool
207 joinable() const noexcept
208 { return !(_M_id == id()); }
209
210 void
211 join();
212
213 void
214 detach();
215
216 id
217 get_id() const noexcept
218 { return _M_id; }
219
220 /** @pre thread is joinable
221 */
222 native_handle_type
223 native_handle()
224 { return _M_id._M_thread; }
225
226 // Returns a value that hints at the number of hardware thread contexts.
227 static unsigned int
228 hardware_concurrency() noexcept;
229
230#ifdef _GLIBCXX_HAS_GTHREADS
231#ifndef _GLIBCXX_THREAD_IMPL
232 private:
233#endif
234 // Abstract base class for types that wrap arbitrary functors to be
235 // invoked in the new thread of execution.
236 struct _State
237 {
238 virtual ~_State();
239 virtual void _M_run() = 0;
240 };
241 using _State_ptr = unique_ptr<_State>;
242
243 private:
244 template<typename _Callable>
245 struct _State_impl : public _State
246 {
247 _Callable _M_func;
248
249 template<typename... _Args>
250 _State_impl(_Args&&... __args)
251 : _M_func(std::forward<_Args>(__args)...)
252 { }
253
254 void
255 _M_run() { _M_func(); }
256 };
257
258 void
259 _M_start_thread(_State_ptr, void (*)());
260
261#if _GLIBCXX_THREAD_ABI_COMPAT
262 public:
263 struct _Impl_base;
264 typedef shared_ptr<_Impl_base> __shared_base_type;
265 struct _Impl_base
266 {
267 __shared_base_type _M_this_ptr;
268 virtual ~_Impl_base() = default;
269 virtual void _M_run() = 0;
270 };
271
272 private:
273 void
274 _M_start_thread(__shared_base_type, void (*)());
275
276 void
277 _M_start_thread(__shared_base_type);
278#endif
279
280 private:
281 // A call wrapper that does INVOKE(forwarded tuple elements...)
282 template<typename _Tuple>
283 struct _Invoker
284 {
285 template<typename... _Args>
286 explicit
287 _Invoker(_Args&&... __args)
288 : _M_t(std::forward<_Args>(__args)...)
289 { }
290
291 _Tuple _M_t;
292
293 template<typename>
294 struct __result;
295 template<typename _Fn, typename... _Args>
296 struct __result<tuple<_Fn, _Args...>>
297 : __invoke_result<_Fn, _Args...>
298 { };
299
300 template<size_t... _Ind>
301 typename __result<_Tuple>::type
302 _M_invoke(_Index_tuple<_Ind...>)
303 { return std::__invoke(std::get<_Ind>(std::move(_M_t))...); }
304
305 typename __result<_Tuple>::type
306 operator()()
307 {
308 using _Indices
309 = typename _Build_index_tuple<tuple_size<_Tuple>::value>::__type;
310 return _M_invoke(_Indices());
311 }
312 };
313
314 public:
315 /// @cond undocumented
316 template<typename... _Tp>
317 using _Call_wrapper = _Invoker<tuple<typename decay<_Tp>::type...>>;
318 /// @endcond
319#endif // _GLIBCXX_HAS_GTHREADS
320 };
321
322#ifndef _GLIBCXX_HAS_GTHREADS
323 inline void thread::join() { std::__throw_system_error(EINVAL); }
324 inline void thread::detach() { std::__throw_system_error(EINVAL); }
325 inline unsigned int thread::hardware_concurrency() noexcept { return 0; }
326#endif
327
328 /// @relates std::thread
329 inline void
330 swap(thread& __x, thread& __y) noexcept
331 { __x.swap(__y); }
332
333 /// @relates std::thread::id
334 inline bool
335 operator==(thread::id __x, thread::id __y) noexcept
336 {
337 // pthread_equal is undefined if either thread ID is not valid, so we
338 // can't safely use __gthread_equal on default-constructed values (nor
339 // the non-zero value returned by this_thread::get_id() for
340 // single-threaded programs using GNU libc). Assume EqualityComparable.
341 return __x._M_thread == __y._M_thread;
342 }
343
344 // N.B. other comparison operators are defined in <thread>
345
346 // DR 889.
347 /// std::hash specialization for thread::id.
348 template<>
349 struct hash<thread::id>
350 : public __hash_base<size_t, thread::id>
351 {
352 size_t
353 operator()(const thread::id& __id) const noexcept
354 { return std::_Hash_impl::hash(__id._M_thread); }
355 };
356
357 namespace this_thread
358 {
359 /// The unique identifier of the current thread.
360 inline thread::id
361 get_id() noexcept
362 {
363#ifndef _GLIBCXX_HAS_GTHREADS
364 return thread::id(1);
365#elif defined _GLIBCXX_NATIVE_THREAD_ID
366 return thread::id(_GLIBCXX_NATIVE_THREAD_ID);
367#else
368 return thread::id(__gthread_self());
369#endif
370 }
371
372 /// Allow the implementation to schedule a different thread.
373 inline void
374 yield() noexcept
375 {
376#if defined _GLIBCXX_HAS_GTHREADS && defined _GLIBCXX_USE_SCHED_YIELD
377 __gthread_yield();
378#endif
379 }
380
381 } // namespace this_thread
382
383 /// @}
384
385_GLIBCXX_END_NAMESPACE_VERSION
386} // namespace
387#endif // C++11
388
389#endif // _GLIBCXX_THREAD_H
tuple
functexcept.h
functional_hash.h
invoke.h
refwrap.h
unique_ptr.h
c++config.h
std::move
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition move.h:138
std::__invoke
constexpr __invoke_result< _Callable, _Args... >::type __invoke(_Callable &&__fn, _Args &&... __args) noexcept(__is_nothrow_invocable< _Callable, _Args... >::value)
Invoke a callable object.
Definition invoke.h:92
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::this_thread
ISO C++ 2011 namespace for interacting with the current thread.
Definition std_thread.h:358
std::this_thread::yield
void yield() noexcept
Allow the implementation to schedule a different thread.
Definition std_thread.h:374
std::this_thread::get_id
thread::id get_id() noexcept
The unique identifier of the current thread.
Definition std_thread.h:361
std::hash
Primary class template hash.
Definition functional_hash.h:106
std::basic_ostream
Template class basic_ostream.
Definition ostream.h:72
std::thread
Definition std_thread.h:85
std::thread::native_handle
native_handle_type native_handle()
Definition std_thread.h:223
std::thread::id
Definition std_thread.h:99