libstdc++
atomic_timed_wait.h
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1// -*- C++ -*- header.
2
3// Copyright (C) 2020-2021 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_timed_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_TIMED_WAIT_H
31#define _GLIBCXX_ATOMIC_TIMED_WAIT_H 1
32
33#pragma GCC system_header
34
35#include <bits/atomic_wait.h>
36
37#if __cpp_lib_atomic_wait
40
41#include <chrono>
42
43#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
44#include <exception> // std::terminate
45#include <sys/time.h>
46#endif
47
48namespace std _GLIBCXX_VISIBILITY(default)
49{
50_GLIBCXX_BEGIN_NAMESPACE_VERSION
51
52 namespace __detail
53 {
54 using __wait_clock_t = chrono::steady_clock;
55
56 template<typename _Clock, typename _Dur>
57 __wait_clock_t::time_point
58 __to_wait_clock(const chrono::time_point<_Clock, _Dur>& __atime) noexcept
59 {
60 const typename _Clock::time_point __c_entry = _Clock::now();
61 const __wait_clock_t::time_point __w_entry = __wait_clock_t::now();
62 const auto __delta = __atime - __c_entry;
63 using __w_dur = typename __wait_clock_t::duration;
64 return __w_entry + chrono::ceil<__w_dur>(__delta);
65 }
66
67 template<typename _Dur>
68 __wait_clock_t::time_point
69 __to_wait_clock(const chrono::time_point<__wait_clock_t,
70 _Dur>& __atime) noexcept
71 {
72 using __w_dur = typename __wait_clock_t::duration;
73 return chrono::ceil<__w_dur>(__atime);
74 }
75
76#ifdef _GLIBCXX_HAVE_LINUX_FUTEX
77#define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
78 // returns true if wait ended before timeout
79 template<typename _Dur>
80 bool
81 __platform_wait_until_impl(const __platform_wait_t* __addr,
82 __platform_wait_t __old,
83 const chrono::time_point<__wait_clock_t, _Dur>&
84 __atime) noexcept
85 {
86 auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
87 auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
88
89 struct timespec __rt =
90 {
91 static_cast<std::time_t>(__s.time_since_epoch().count()),
92 static_cast<long>(__ns.count())
93 };
94
95 auto __e = syscall (SYS_futex, __addr,
96 static_cast<int>(__futex_wait_flags::
97 __wait_bitset_private),
98 __old, &__rt, nullptr,
99 static_cast<int>(__futex_wait_flags::
100 __bitset_match_any));
101
102 if (__e)
103 {
104 if (errno == ETIMEDOUT)
105 return false;
106 if (errno != EINTR && errno != EAGAIN)
107 __throw_system_error(errno);
108 }
109 return true;
110 }
111
112 // returns true if wait ended before timeout
113 template<typename _Clock, typename _Dur>
114 bool
115 __platform_wait_until(const __platform_wait_t* __addr, __platform_wait_t __old,
116 const chrono::time_point<_Clock, _Dur>& __atime)
117 {
118 if constexpr (is_same_v<__wait_clock_t, _Clock>)
119 {
120 return __platform_wait_until_impl(__addr, __old, __atime);
121 }
122 else
123 {
124 if (!__platform_wait_until_impl(__addr, __old,
125 __to_wait_clock(__atime)))
126 {
127 // We got a timeout when measured against __clock_t but
128 // we need to check against the caller-supplied clock
129 // to tell whether we should return a timeout.
130 if (_Clock::now() < __atime)
131 return true;
132 }
133 return false;
134 }
135 }
136#else
137// define _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT and implement __platform_wait_until()
138// if there is a more efficient primitive supported by the platform
139// (e.g. __ulock_wait())which is better than pthread_cond_clockwait
140#endif // ! PLATFORM_TIMED_WAIT
141
142#ifdef _GLIBCXX_HAS_GTHREADS
143 // Returns true if wait ended before timeout.
144 // _Clock must be either steady_clock or system_clock.
145 template<typename _Clock, typename _Dur>
146 bool
147 __cond_wait_until_impl(__condvar& __cv, mutex& __mx,
148 const chrono::time_point<_Clock, _Dur>& __atime)
149 {
150 static_assert(std::__is_one_of<_Clock, chrono::steady_clock,
151 chrono::system_clock>::value);
152
153 auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
154 auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
155
156 __gthread_time_t __ts =
157 {
158 static_cast<std::time_t>(__s.time_since_epoch().count()),
159 static_cast<long>(__ns.count())
160 };
161
162#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
163 if constexpr (is_same_v<chrono::steady_clock, _Clock>)
164 __cv.wait_until(__mx, CLOCK_MONOTONIC, __ts);
165 else
166#endif
167 __cv.wait_until(__mx, __ts);
168 return _Clock::now() < __atime;
169 }
170
171 // returns true if wait ended before timeout
172 template<typename _Clock, typename _Dur>
173 bool
174 __cond_wait_until(__condvar& __cv, mutex& __mx,
175 const chrono::time_point<_Clock, _Dur>& __atime)
176 {
177#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
178 if constexpr (is_same_v<_Clock, chrono::steady_clock>)
179 return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
180 else
181#endif
182 if constexpr (is_same_v<_Clock, chrono::system_clock>)
183 return __detail::__cond_wait_until_impl(__cv, __mx, __atime);
184 else
185 {
186 if (__cond_wait_until_impl(__cv, __mx,
187 __to_wait_clock(__atime)))
188 {
189 // We got a timeout when measured against __clock_t but
190 // we need to check against the caller-supplied clock
191 // to tell whether we should return a timeout.
192 if (_Clock::now() < __atime)
193 return true;
194 }
195 return false;
196 }
197 }
198#endif // _GLIBCXX_HAS_GTHREADS
199
200 struct __timed_waiter_pool : __waiter_pool_base
201 {
202 // returns true if wait ended before timeout
203 template<typename _Clock, typename _Dur>
204 bool
205 _M_do_wait_until(__platform_wait_t* __addr, __platform_wait_t __old,
206 const chrono::time_point<_Clock, _Dur>& __atime)
207 {
208#ifdef _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
209 return __platform_wait_until(__addr, __old, __atime);
210#else
211 __platform_wait_t __val;
212 __atomic_load(__addr, &__val, __ATOMIC_RELAXED);
213 if (__val == __old)
214 {
215 lock_guard<mutex> __l(_M_mtx);
216 return __cond_wait_until(_M_cv, _M_mtx, __atime);
217 }
218 else
219 return true;
220#endif // _GLIBCXX_HAVE_PLATFORM_TIMED_WAIT
221 }
222 };
223
224 struct __timed_backoff_spin_policy
225 {
226 __wait_clock_t::time_point _M_deadline;
227 __wait_clock_t::time_point _M_t0;
228
229 template<typename _Clock, typename _Dur>
230 __timed_backoff_spin_policy(chrono::time_point<_Clock, _Dur>
231 __deadline = _Clock::time_point::max(),
232 chrono::time_point<_Clock, _Dur>
233 __t0 = _Clock::now()) noexcept
234 : _M_deadline(__to_wait_clock(__deadline))
235 , _M_t0(__to_wait_clock(__t0))
236 { }
237
238 bool
239 operator()() const noexcept
240 {
241 using namespace literals::chrono_literals;
242 auto __now = __wait_clock_t::now();
243 if (_M_deadline <= __now)
244 return false;
245
246 // FIXME: this_thread::sleep_for not available #ifdef _GLIBCXX_NO_SLEEP
247
248 auto __elapsed = __now - _M_t0;
249 if (__elapsed > 128ms)
250 {
252 }
253 else if (__elapsed > 64us)
254 {
255 this_thread::sleep_for(__elapsed / 2);
256 }
257 else if (__elapsed > 4us)
258 {
259 __thread_yield();
260 }
261 else
262 return false;
263 return true;
264 }
265 };
266
267 template<typename _EntersWait>
268 struct __timed_waiter : __waiter_base<__timed_waiter_pool>
269 {
270 using __base_type = __waiter_base<__timed_waiter_pool>;
271
272 template<typename _Tp>
273 __timed_waiter(const _Tp* __addr) noexcept
274 : __base_type(__addr)
275 {
276 if constexpr (_EntersWait::value)
277 _M_w._M_enter_wait();
278 }
279
280 ~__timed_waiter()
281 {
282 if constexpr (_EntersWait::value)
283 _M_w._M_leave_wait();
284 }
285
286 // returns true if wait ended before timeout
287 template<typename _Tp, typename _ValFn,
288 typename _Clock, typename _Dur>
289 bool
290 _M_do_wait_until_v(_Tp __old, _ValFn __vfn,
291 const chrono::time_point<_Clock, _Dur>&
292 __atime) noexcept
293 {
294 __platform_wait_t __val;
295 if (_M_do_spin(__old, std::move(__vfn), __val,
296 __timed_backoff_spin_policy(__atime)))
297 return true;
298 return __base_type::_M_w._M_do_wait_until(__base_type::_M_addr, __val, __atime);
299 }
300
301 // returns true if wait ended before timeout
302 template<typename _Pred,
303 typename _Clock, typename _Dur>
304 bool
305 _M_do_wait_until(_Pred __pred, __platform_wait_t __val,
306 const chrono::time_point<_Clock, _Dur>&
307 __atime) noexcept
308 {
309 for (auto __now = _Clock::now(); __now < __atime;
310 __now = _Clock::now())
311 {
312 if (__base_type::_M_w._M_do_wait_until(
313 __base_type::_M_addr, __val, __atime)
314 && __pred())
315 return true;
316
317 if (__base_type::_M_do_spin(__pred, __val,
318 __timed_backoff_spin_policy(__atime, __now)))
319 return true;
320 }
321 return false;
322 }
323
324 // returns true if wait ended before timeout
325 template<typename _Pred,
326 typename _Clock, typename _Dur>
327 bool
328 _M_do_wait_until(_Pred __pred,
329 const chrono::time_point<_Clock, _Dur>&
330 __atime) noexcept
331 {
332 __platform_wait_t __val;
333 if (__base_type::_M_do_spin(__pred, __val,
334 __timed_backoff_spin_policy(__atime)))
335 return true;
336 return _M_do_wait_until(__pred, __val, __atime);
337 }
338
339 template<typename _Tp, typename _ValFn,
340 typename _Rep, typename _Period>
341 bool
342 _M_do_wait_for_v(_Tp __old, _ValFn __vfn,
343 const chrono::duration<_Rep, _Period>&
344 __rtime) noexcept
345 {
346 __platform_wait_t __val;
347 if (_M_do_spin_v(__old, std::move(__vfn), __val))
348 return true;
349
350 if (!__rtime.count())
351 return false; // no rtime supplied, and spin did not acquire
352
353 auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);
354
355 return __base_type::_M_w._M_do_wait_until(
356 __base_type::_M_addr,
357 __val,
358 chrono::steady_clock::now() + __reltime);
359 }
360
361 template<typename _Pred,
362 typename _Rep, typename _Period>
363 bool
364 _M_do_wait_for(_Pred __pred,
365 const chrono::duration<_Rep, _Period>& __rtime) noexcept
366 {
367 __platform_wait_t __val;
368 if (__base_type::_M_do_spin(__pred, __val))
369 return true;
370
371 if (!__rtime.count())
372 return false; // no rtime supplied, and spin did not acquire
373
374 auto __reltime = chrono::ceil<__wait_clock_t::duration>(__rtime);
375
376 return _M_do_wait_until(__pred, __val,
377 chrono::steady_clock::now() + __reltime);
378 }
379 };
380
381 using __enters_timed_wait = __timed_waiter<std::true_type>;
382 using __bare_timed_wait = __timed_waiter<std::false_type>;
383 } // namespace __detail
384
385 // returns true if wait ended before timeout
386 template<typename _Tp, typename _ValFn,
387 typename _Clock, typename _Dur>
388 bool
389 __atomic_wait_address_until_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
390 const chrono::time_point<_Clock, _Dur>&
391 __atime) noexcept
392 {
393 __detail::__enters_timed_wait __w{__addr};
394 return __w._M_do_wait_until_v(__old, __vfn, __atime);
395 }
396
397 template<typename _Tp, typename _Pred,
398 typename _Clock, typename _Dur>
399 bool
400 __atomic_wait_address_until(const _Tp* __addr, _Pred __pred,
401 const chrono::time_point<_Clock, _Dur>&
402 __atime) noexcept
403 {
404 __detail::__enters_timed_wait __w{__addr};
405 return __w._M_do_wait_until(__pred, __atime);
406 }
407
408 template<typename _Pred,
409 typename _Clock, typename _Dur>
410 bool
411 __atomic_wait_address_until_bare(const __detail::__platform_wait_t* __addr,
412 _Pred __pred,
413 const chrono::time_point<_Clock, _Dur>&
414 __atime) noexcept
415 {
416 __detail::__bare_timed_wait __w{__addr};
417 return __w._M_do_wait_until(__pred, __atime);
418 }
419
420 template<typename _Tp, typename _ValFn,
421 typename _Rep, typename _Period>
422 bool
423 __atomic_wait_address_for_v(const _Tp* __addr, _Tp&& __old, _ValFn&& __vfn,
424 const chrono::duration<_Rep, _Period>& __rtime) noexcept
425 {
426 __detail::__enters_timed_wait __w{__addr};
427 return __w._M_do_wait_for_v(__old, __vfn, __rtime);
428 }
429
430 template<typename _Tp, typename _Pred,
431 typename _Rep, typename _Period>
432 bool
433 __atomic_wait_address_for(const _Tp* __addr, _Pred __pred,
434 const chrono::duration<_Rep, _Period>& __rtime) noexcept
435 {
436
437 __detail::__enters_timed_wait __w{__addr};
438 return __w._M_do_wait_for(__pred, __rtime);
439 }
440
441 template<typename _Pred,
442 typename _Rep, typename _Period>
443 bool
444 __atomic_wait_address_for_bare(const __detail::__platform_wait_t* __addr,
445 _Pred __pred,
446 const chrono::duration<_Rep, _Period>& __rtime) noexcept
447 {
448 __detail::__bare_timed_wait __w{__addr};
449 return __w._M_do_wait_for(__pred, __rtime);
450 }
451_GLIBCXX_END_NAMESPACE_VERSION
452} // namespace std
453#endif // __cpp_lib_atomic_wait
454#endif // _GLIBCXX_ATOMIC_TIMED_WAIT_H
constexpr std::remove_reference< _Tp >::type && move(_Tp &&__t) noexcept
Convert a value to an rvalue.
Definition: move.h:104
ISO C++ entities toplevel namespace is std.
void sleep_for(const chrono::duration< _Rep, _Period > &__rtime)
this_thread::sleep_for