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83a1beee TR |
1 | // -*- C++ -*- header. |
2 | ||
3 | // Copyright (C) 2020 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/atomic_wait.h | |
26 | * This is an internal header file, included by other library headers. | |
27 | * Do not attempt to use it directly. @headername{atomic} | |
28 | */ | |
29 | ||
30 | #ifndef _GLIBCXX_ATOMIC_WAIT_H | |
31 | #define _GLIBCXX_ATOMIC_WAIT_H 1 | |
32 | ||
33 | #pragma GCC system_header | |
34 | ||
35 | #include <bits/c++config.h> | |
183ae52b | 36 | #if defined _GLIBCXX_HAS_GTHREADS || _GLIBCXX_HAVE_LINUX_FUTEX |
83a1beee TR |
37 | #include <bits/functional_hash.h> |
38 | #include <bits/gthr.h> | |
39 | #include <bits/std_mutex.h> | |
40 | #include <bits/unique_lock.h> | |
41 | #include <ext/numeric_traits.h> | |
42 | ||
43 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX | |
44 | #include <climits> | |
45 | #include <unistd.h> | |
46 | #include <syscall.h> | |
47 | #endif | |
48 | ||
49 | ||
50 | // TODO get this from Autoconf | |
51 | #define _GLIBCXX_HAVE_LINUX_FUTEX_PRIVATE 1 | |
52 | ||
53 | namespace std _GLIBCXX_VISIBILITY(default) | |
54 | { | |
55 | _GLIBCXX_BEGIN_NAMESPACE_VERSION | |
56 | namespace __detail | |
57 | { | |
58 | using __platform_wait_t = int; | |
59 | ||
60 | constexpr auto __atomic_spin_count_1 = 16; | |
61 | constexpr auto __atomic_spin_count_2 = 12; | |
62 | ||
63 | inline constexpr | |
64 | auto __platform_wait_max_value = | |
65 | __gnu_cxx::__int_traits<__platform_wait_t>::__max; | |
66 | ||
67 | template<typename _Tp> | |
68 | inline constexpr bool __platform_wait_uses_type | |
69 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX | |
70 | = is_same_v<remove_cv_t<_Tp>, __platform_wait_t>; | |
71 | #else | |
72 | = false; | |
73 | #endif | |
74 | ||
75 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX | |
76 | enum class __futex_wait_flags : int | |
77 | { | |
78 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX_PRIVATE | |
79 | __private_flag = 128, | |
80 | #else | |
81 | __private_flag = 0, | |
82 | #endif | |
83 | __wait = 0, | |
84 | __wake = 1, | |
85 | __wait_bitset = 9, | |
86 | __wake_bitset = 10, | |
87 | __wait_private = __wait | __private_flag, | |
88 | __wake_private = __wake | __private_flag, | |
89 | __wait_bitset_private = __wait_bitset | __private_flag, | |
90 | __wake_bitset_private = __wake_bitset | __private_flag, | |
91 | __bitset_match_any = -1 | |
92 | }; | |
93 | ||
94 | template<typename _Tp> | |
95 | void | |
96 | __platform_wait(const _Tp* __addr, __platform_wait_t __val) noexcept | |
97 | { | |
98 | for(;;) | |
99 | { | |
100 | auto __e = syscall (SYS_futex, static_cast<const void*>(__addr), | |
101 | static_cast<int>(__futex_wait_flags::__wait_private), | |
102 | __val, nullptr); | |
a5ccfd04 | 103 | if (!__e || errno == EAGAIN) |
83a1beee | 104 | break; |
ad9cbcee | 105 | else if (errno != EINTR) |
83a1beee TR |
106 | __throw_system_error(__e); |
107 | } | |
108 | } | |
109 | ||
183ae52b | 110 | template<typename _Tp> |
83a1beee TR |
111 | void |
112 | __platform_notify(const _Tp* __addr, bool __all) noexcept | |
113 | { | |
114 | syscall (SYS_futex, static_cast<const void*>(__addr), | |
115 | static_cast<int>(__futex_wait_flags::__wake_private), | |
116 | __all ? INT_MAX : 1); | |
117 | } | |
118 | #endif | |
119 | ||
120 | struct __waiters | |
121 | { | |
122 | alignas(64) __platform_wait_t _M_ver = 0; | |
123 | alignas(64) __platform_wait_t _M_wait = 0; | |
124 | ||
125 | #ifndef _GLIBCXX_HAVE_LINUX_FUTEX | |
126 | using __lock_t = std::unique_lock<std::mutex>; | |
127 | mutable __lock_t::mutex_type _M_mtx; | |
128 | ||
129 | # ifdef __GTHREAD_COND_INIT | |
130 | mutable __gthread_cond_t _M_cv = __GTHREAD_COND_INIT; | |
131 | __waiters() noexcept = default; | |
132 | # else | |
133 | mutable __gthread_cond_t _M_cv; | |
134 | __waiters() noexcept | |
135 | { | |
a5ccfd04 | 136 | __GTHREAD_COND_INIT_FUNCTION(&_M_cv); |
83a1beee TR |
137 | } |
138 | # endif | |
139 | #endif | |
140 | ||
141 | __platform_wait_t | |
142 | _M_enter_wait() noexcept | |
143 | { | |
144 | __platform_wait_t __res; | |
145 | __atomic_load(&_M_ver, &__res, __ATOMIC_ACQUIRE); | |
146 | __atomic_fetch_add(&_M_wait, 1, __ATOMIC_ACQ_REL); | |
147 | return __res; | |
148 | } | |
149 | ||
150 | void | |
151 | _M_leave_wait() noexcept | |
152 | { | |
153 | __atomic_fetch_sub(&_M_wait, 1, __ATOMIC_ACQ_REL); | |
154 | } | |
155 | ||
156 | void | |
157 | _M_do_wait(__platform_wait_t __version) noexcept | |
158 | { | |
159 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX | |
160 | __platform_wait(&_M_ver, __version); | |
161 | #else | |
162 | __platform_wait_t __cur = 0; | |
163 | while (__cur <= __version) | |
164 | { | |
165 | __waiters::__lock_t __l(_M_mtx); | |
166 | auto __e = __gthread_cond_wait(&_M_cv, __l.mutex()->native_handle()); | |
167 | if (__e) | |
168 | __throw_system_error(__e); | |
169 | __platform_wait_t __last = __cur; | |
170 | __atomic_load(&_M_ver, &__cur, __ATOMIC_ACQUIRE); | |
171 | if (__cur < __last) | |
172 | break; // break the loop if version overflows | |
173 | } | |
174 | #endif | |
175 | } | |
176 | ||
177 | bool | |
178 | _M_waiting() const noexcept | |
183ae52b JW |
179 | { |
180 | __platform_wait_t __res; | |
181 | __atomic_load(&_M_wait, &__res, __ATOMIC_ACQUIRE); | |
182 | return __res; | |
183 | } | |
83a1beee TR |
184 | |
185 | void | |
186 | _M_notify(bool __all) noexcept | |
187 | { | |
188 | __atomic_fetch_add(&_M_ver, 1, __ATOMIC_ACQ_REL); | |
189 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX | |
190 | __platform_notify(&_M_ver, __all); | |
191 | #else | |
192 | auto __e = __gthread_cond_broadcast(&_M_cv); | |
193 | if (__e) | |
194 | __throw_system_error(__e); | |
195 | #endif | |
196 | } | |
197 | ||
198 | static __waiters& | |
199 | _S_for(const void* __t) | |
200 | { | |
201 | const unsigned char __mask = 0xf; | |
202 | static __waiters __w[__mask + 1]; | |
203 | ||
204 | auto __key = _Hash_impl::hash(__t) & __mask; | |
205 | return __w[__key]; | |
206 | } | |
207 | }; | |
208 | ||
209 | struct __waiter | |
210 | { | |
211 | __waiters& _M_w; | |
212 | __platform_wait_t _M_version; | |
213 | ||
214 | template<typename _Tp> | |
215 | __waiter(const _Tp* __addr) noexcept | |
216 | : _M_w(__waiters::_S_for(static_cast<const void*>(__addr))) | |
217 | , _M_version(_M_w._M_enter_wait()) | |
218 | { } | |
219 | ||
220 | ~__waiter() | |
221 | { _M_w._M_leave_wait(); } | |
222 | ||
223 | void _M_do_wait() noexcept | |
224 | { _M_w._M_do_wait(_M_version); } | |
225 | }; | |
226 | ||
0986d3bc | 227 | inline void |
83a1beee TR |
228 | __thread_relax() noexcept |
229 | { | |
230 | #if defined __i386__ || defined __x86_64__ | |
231 | __builtin_ia32_pause(); | |
232 | #elif defined _GLIBCXX_USE_SCHED_YIELD | |
233 | __gthread_yield(); | |
234 | #endif | |
235 | } | |
236 | ||
0986d3bc | 237 | inline void |
83a1beee | 238 | __thread_yield() noexcept |
0986d3bc | 239 | { |
83a1beee TR |
240 | #if defined _GLIBCXX_USE_SCHED_YIELD |
241 | __gthread_yield(); | |
242 | #endif | |
243 | } | |
244 | ||
245 | } // namespace __detail | |
246 | ||
247 | template<typename _Pred> | |
248 | bool | |
249 | __atomic_spin(_Pred& __pred) noexcept | |
250 | { | |
251 | for (auto __i = 0; __i < __detail::__atomic_spin_count_1; ++__i) | |
252 | { | |
253 | if (__pred()) | |
254 | return true; | |
255 | ||
256 | if (__i < __detail::__atomic_spin_count_2) | |
257 | __detail::__thread_relax(); | |
258 | else | |
259 | __detail::__thread_yield(); | |
260 | } | |
261 | return false; | |
262 | } | |
263 | ||
264 | template<typename _Tp, typename _Pred> | |
265 | void | |
266 | __atomic_wait(const _Tp* __addr, _Tp __old, _Pred __pred) noexcept | |
267 | { | |
268 | using namespace __detail; | |
269 | if (std::__atomic_spin(__pred)) | |
270 | return; | |
271 | ||
272 | __waiter __w(__addr); | |
273 | while (!__pred()) | |
274 | { | |
275 | if constexpr (__platform_wait_uses_type<_Tp>) | |
276 | { | |
277 | __platform_wait(__addr, __old); | |
278 | } | |
279 | else | |
280 | { | |
281 | // TODO support timed backoff when this can be moved into the lib | |
282 | __w._M_do_wait(); | |
283 | } | |
284 | } | |
285 | } | |
286 | ||
287 | template<typename _Tp> | |
288 | void | |
289 | __atomic_notify(const _Tp* __addr, bool __all) noexcept | |
290 | { | |
291 | using namespace __detail; | |
292 | auto& __w = __waiters::_S_for((void*)__addr); | |
293 | if (!__w._M_waiting()) | |
294 | return; | |
295 | ||
62d19588 | 296 | #ifdef _GLIBCXX_HAVE_LINUX_FUTEX |
83a1beee TR |
297 | if constexpr (__platform_wait_uses_type<_Tp>) |
298 | { | |
299 | __platform_notify((__platform_wait_t*)(void*) __addr, __all); | |
300 | } | |
301 | else | |
62d19588 | 302 | #endif |
83a1beee TR |
303 | { |
304 | __w._M_notify(__all); | |
305 | } | |
306 | } | |
307 | _GLIBCXX_END_NAMESPACE_VERSION | |
308 | } // namespace std | |
183ae52b JW |
309 | #endif // GTHREADS || LINUX_FUTEX |
310 | #endif // _GLIBCXX_ATOMIC_WAIT_H |