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