1// std::mutex implementation -*- C++ -*-
2
3// Copyright (C) 2003-2026 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_mutex.h
26 * This is an internal header file, included by other library headers.
27 * Do not attempt to use it directly. @headername{mutex}
28 */
29
30#ifndef _GLIBCXX_MUTEX_H
31#define _GLIBCXX_MUTEX_H 1
32
33#ifdef _GLIBCXX_SYSHDR
34#pragma GCC system_header
35#endif
36
37#if __cplusplus < 201103L
38# include <bits/c++0x_warning.h>
39#else
40
41#include <errno.h> // EBUSY
42#include <bits/chrono.h>
43#include <bits/functexcept.h>
44#include <bits/gthr.h>
45
46namespace std _GLIBCXX_VISIBILITY(default)
47{
48_GLIBCXX_BEGIN_NAMESPACE_VERSION
49
50 /**
51 * @defgroup mutexes Mutexes
52 * @ingroup concurrency
53 *
54 * Classes for mutex support.
55 * @{
56 */
57
58#ifdef _GLIBCXX_HAS_GTHREADS
59 /// @cond undocumented
60
61 // Common base class for std::mutex and std::timed_mutex
62 class __mutex_base
63 {
64 protected:
65 typedef __gthread_mutex_t __native_type;
66
67#ifdef __GTHREAD_MUTEX_INIT
68 __native_type _M_mutex = __GTHREAD_MUTEX_INIT;
69
70 constexpr __mutex_base() noexcept = default;
71#else
72 __native_type _M_mutex;
73
74 __mutex_base() noexcept
75 {
76 // XXX EAGAIN, ENOMEM, EPERM, EBUSY(may), EINVAL(may)
77 __GTHREAD_MUTEX_INIT_FUNCTION(&_M_mutex);
78 }
79
80 ~__mutex_base() noexcept { __gthread_mutex_destroy(&_M_mutex); }
81#endif
82
83 __mutex_base(const __mutex_base&) = delete;
84 __mutex_base& operator=(const __mutex_base&) = delete;
85 };
86 /// @endcond
87
88 /** The standard mutex type.
89 *
90 * A simple, non-recursive, non-timed mutex.
91 *
92 * Do not call `lock()` and `unlock()` directly, use a scoped lock type
93 * such as `std::unique_lock`, `std::lock_guard`, or (since C++17)
94 * `std::scoped_lock`.
95 *
96 * @headerfile mutex
97 * @since C++11
98 */
99 class mutex : private __mutex_base
100 {
101 public:
102 typedef __native_type* native_handle_type;
103
104#ifdef __GTHREAD_MUTEX_INIT
105 constexpr
106#endif
107 mutex() noexcept = default;
108 ~mutex() = default;
109
110 mutex(const mutex&) = delete;
111 mutex& operator=(const mutex&) = delete;
112
113 void
114 lock()
115 {
116 int __e = __gthread_mutex_lock(mutex: &_M_mutex);
117
118 // EINVAL, EAGAIN, EBUSY, EINVAL, EDEADLK(may)
119 if (__e)
120 __throw_system_error(__e);
121 }
122
123 _GLIBCXX_NODISCARD
124 bool
125 try_lock() noexcept
126 {
127 // XXX EINVAL, EAGAIN, EBUSY
128 return !__gthread_mutex_trylock(mutex: &_M_mutex);
129 }
130
131 void
132 unlock()
133 {
134 // XXX EINVAL, EAGAIN, EPERM
135 __gthread_mutex_unlock(mutex: &_M_mutex);
136 }
137
138 native_handle_type
139 native_handle() noexcept
140 { return &_M_mutex; }
141 };
142
143 /// @cond undocumented
144
145 // Implementation details for std::condition_variable
146 class __condvar
147 {
148 using timespec = __gthread_time_t;
149
150 public:
151 __condvar() noexcept
152 {
153#ifndef __GTHREAD_COND_INIT
154 __GTHREAD_COND_INIT_FUNCTION(&_M_cond);
155#endif
156 }
157
158 ~__condvar()
159 {
160 int __e __attribute__((__unused__)) = __gthread_cond_destroy(cond: &_M_cond);
161 __glibcxx_assert(__e != EBUSY); // threads are still blocked
162 }
163
164 __condvar(const __condvar&) = delete;
165 __condvar& operator=(const __condvar&) = delete;
166
167 __gthread_cond_t* native_handle() noexcept { return &_M_cond; }
168
169 // Expects: Calling thread has locked __m.
170 void
171 wait(mutex& __m)
172 {
173 int __e __attribute__((__unused__))
174 = __gthread_cond_wait(cond: &_M_cond, mutex: __m.native_handle());
175 __glibcxx_assert(__e == 0);
176 }
177
178 void
179 wait_until(mutex& __m, timespec& __abs_time)
180 {
181 __gthread_cond_timedwait(cond: &_M_cond, mutex: __m.native_handle(), abs_timeout: &__abs_time);
182 }
183
184#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
185 void
186 wait_until(mutex& __m, clockid_t __clock, timespec& __abs_time)
187 {
188 pthread_cond_clockwait(cond: &_M_cond, mutex: __m.native_handle(), clock_id: __clock,
189 abstime: &__abs_time);
190 }
191#endif
192
193 void
194 notify_one() noexcept
195 {
196 int __e __attribute__((__unused__)) = __gthread_cond_signal(cond: &_M_cond);
197 __glibcxx_assert(__e == 0);
198 }
199
200 void
201 notify_all() noexcept
202 {
203 int __e __attribute__((__unused__)) = __gthread_cond_broadcast(cond: &_M_cond);
204 __glibcxx_assert(__e == 0);
205 }
206
207 protected:
208#ifdef __GTHREAD_COND_INIT
209 __gthread_cond_t _M_cond = __GTHREAD_COND_INIT;
210#else
211 __gthread_cond_t _M_cond;
212#endif
213 };
214
215namespace chrono
216{
217#pragma GCC diagnostic push
218#pragma GCC diagnostic ignored "-Wc++17-extensions"
219 // Convert a time_point to an absolute time represented as __gthread_time_t
220 // (which is typically just a typedef for struct timespec).
221 template<typename _Clock, typename _Dur>
222 [[__nodiscard__]] _GLIBCXX14_CONSTEXPR inline
223 __gthread_time_t
224 __to_timeout_gthread_time_t(const time_point<_Clock, _Dur>& __t)
225 {
226 auto __ts = chrono::__to_timeout_timespec(__t.time_since_epoch());
227 if constexpr (is_same<::timespec, __gthread_time_t>::value)
228 return __ts;
229 else if constexpr (is_convertible<::timespec, __gthread_time_t>::value)
230 return __ts;
231 else if constexpr (is_scalar<__gthread_time_t>::value) // Assume seconds:
232 return static_cast<__gthread_time_t>(__ts.tv_sec);
233 else // Assume this works and the members are in the correct order:
234 return __gthread_time_t{ __ts.tv_sec, __ts.tv_nsec };
235 }
236#pragma GCC diagnostic pop
237}
238 /// @endcond
239#endif // _GLIBCXX_HAS_GTHREADS
240
241 /// Do not acquire ownership of the mutex.
242 struct defer_lock_t { explicit defer_lock_t() = default; };
243
244 /// Try to acquire ownership of the mutex without blocking.
245 struct try_to_lock_t { explicit try_to_lock_t() = default; };
246
247 /// Assume the calling thread has already obtained mutex ownership
248 /// and manage it.
249 struct adopt_lock_t { explicit adopt_lock_t() = default; };
250
251 /// Tag used to prevent a scoped lock from acquiring ownership of a mutex.
252 _GLIBCXX17_INLINE constexpr defer_lock_t defer_lock { };
253
254 /// Tag used to prevent a scoped lock from blocking if a mutex is locked.
255 _GLIBCXX17_INLINE constexpr try_to_lock_t try_to_lock { };
256
257 /// Tag used to make a scoped lock take ownership of a locked mutex.
258 _GLIBCXX17_INLINE constexpr adopt_lock_t adopt_lock { };
259
260 /** @brief A simple scoped lock type.
261 *
262 * A lock_guard controls mutex ownership within a scope, releasing
263 * ownership in the destructor.
264 *
265 * @headerfile mutex
266 * @since C++11
267 */
268 template<typename _Mutex>
269 class lock_guard
270 {
271 public:
272 typedef _Mutex mutex_type;
273
274 [[__nodiscard__]]
275 explicit lock_guard(mutex_type& __m) : _M_device(__m)
276 { _M_device.lock(); }
277
278 [[__nodiscard__]]
279 lock_guard(mutex_type& __m, adopt_lock_t) noexcept : _M_device(__m)
280 { } // calling thread owns mutex
281
282 ~lock_guard()
283 { _M_device.unlock(); }
284
285 lock_guard(const lock_guard&) = delete;
286 lock_guard& operator=(const lock_guard&) = delete;
287
288 private:
289 mutex_type& _M_device;
290 };
291
292 /// @} group mutexes
293_GLIBCXX_END_NAMESPACE_VERSION
294} // namespace
295#endif // C++11
296#endif // _GLIBCXX_MUTEX_H
297