1 // <stop_token> -*- C++ -*-
3 // Copyright (C) 2019-2024 Free Software Foundation, Inc.
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)
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.
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.
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/>.
25 /** @file include/stop_token
26 * This is a Standard C++ Library header.
29 #ifndef _GLIBCXX_STOP_TOKEN
30 #define _GLIBCXX_STOP_TOKEN
32 #include <bits/requires_hosted.h> // concurrency
34 #define __glibcxx_want_jthread
35 #include <bits/version.h>
37 #if __cplusplus > 201703L
40 #include <bits/std_thread.h>
44 namespace std _GLIBCXX_VISIBILITY(default)
46 _GLIBCXX_BEGIN_NAMESPACE_VERSION
48 /// Tag type indicating a stop_source should have no shared-stop-state.
49 struct nostopstate_t { explicit nostopstate_t() = default; };
50 inline constexpr nostopstate_t nostopstate{};
54 /// Allow testing whether a stop request has been made on a `stop_source`.
58 stop_token() noexcept = default;
60 stop_token(const stop_token&) noexcept = default;
61 stop_token(stop_token&&) noexcept = default;
63 ~stop_token() = default;
66 operator=(const stop_token&) noexcept = default;
69 operator=(stop_token&&) noexcept = default;
73 stop_possible() const noexcept
75 return static_cast<bool>(_M_state) && _M_state->_M_stop_possible();
80 stop_requested() const noexcept
82 return static_cast<bool>(_M_state) && _M_state->_M_stop_requested();
86 swap(stop_token& __rhs) noexcept
87 { _M_state.swap(__rhs._M_state); }
91 operator==(const stop_token& __a, const stop_token& __b)
92 { return __a._M_state == __b._M_state; }
95 swap(stop_token& __lhs, stop_token& __rhs) noexcept
96 { __lhs.swap(__rhs); }
99 friend class stop_source;
100 template<typename _Callback>
101 friend class stop_callback;
106 #if defined __i386__ || defined __x86_64__
107 __builtin_ia32_pause();
109 this_thread::yield();
112 #ifndef __glibcxx_semaphore
113 struct binary_semaphore
115 explicit binary_semaphore(int __d) : _M_counter(__d > 0) { }
117 void release() { _M_counter.fetch_add(1, memory_order::release); }
122 while (!_M_counter.compare_exchange_weak(__old, 0,
123 memory_order::acquire,
124 memory_order::relaxed))
131 atomic<int> _M_counter;
137 using __cb_type = void(_Stop_cb*) noexcept;
138 __cb_type* _M_callback;
139 _Stop_cb* _M_prev = nullptr;
140 _Stop_cb* _M_next = nullptr;
141 bool* _M_destroyed = nullptr;
142 binary_semaphore _M_done{0};
144 [[__gnu__::__nonnull__]]
146 _Stop_cb(__cb_type* __cb)
150 void _M_run() noexcept { _M_callback(this); }
155 using value_type = uint32_t;
156 static constexpr value_type _S_stop_requested_bit = 1;
157 static constexpr value_type _S_locked_bit = 2;
158 static constexpr value_type _S_ssrc_counter_inc = 4;
160 std::atomic<value_type> _M_owners{1};
161 std::atomic<value_type> _M_value{_S_ssrc_counter_inc};
162 _Stop_cb* _M_head = nullptr;
163 std::thread::id _M_requester;
165 _Stop_state_t() = default;
168 _M_stop_possible() noexcept
170 // true if a stop request has already been made or there are still
171 // stop_source objects that would allow one to be made.
172 return _M_value.load(memory_order::acquire) & ~_S_locked_bit;
176 _M_stop_requested() noexcept
178 return _M_value.load(memory_order::acquire) & _S_stop_requested_bit;
182 _M_add_owner() noexcept
184 _M_owners.fetch_add(1, memory_order::relaxed);
188 _M_release_ownership() noexcept
190 if (_M_owners.fetch_sub(1, memory_order::acq_rel) == 1)
195 _M_add_ssrc() noexcept
197 _M_value.fetch_add(_S_ssrc_counter_inc, memory_order::relaxed);
201 _M_sub_ssrc() noexcept
203 _M_value.fetch_sub(_S_ssrc_counter_inc, memory_order::release);
210 // Can use relaxed loads to get the current value.
211 // The successful call to _M_try_lock is an acquire operation.
212 auto __old = _M_value.load(memory_order::relaxed);
213 while (!_M_try_lock(__old, memory_order::relaxed))
217 // Precondition: calling thread holds the lock.
221 _M_value.fetch_sub(_S_locked_bit, memory_order::release);
225 _M_request_stop() noexcept
227 // obtain lock and set stop_requested bit
228 auto __old = _M_value.load(memory_order::acquire);
231 if (__old & _S_stop_requested_bit) // stop request already made
234 while (!_M_try_lock_and_stop(__old));
236 _M_requester = this_thread::get_id();
241 _Stop_cb* __cb = _M_head;
242 _M_head = _M_head->_M_next;
245 _M_head->_M_prev = nullptr;
251 // Allow other callbacks to be unregistered while __cb runs.
254 bool __destroyed = false;
255 __cb->_M_destroyed = &__destroyed;
262 __cb->_M_destroyed = nullptr;
264 // synchronize with destructor of stop_callback that owns *__cb
265 if (!__gnu_cxx::__is_single_threaded())
266 __cb->_M_done.release();
269 // Avoid relocking if we already know there are no more callbacks.
280 [[__gnu__::__nonnull__]]
282 _M_register_callback(_Stop_cb* __cb) noexcept
284 auto __old = _M_value.load(memory_order::acquire);
287 if (__old & _S_stop_requested_bit) // stop request already made
289 __cb->_M_run(); // run synchronously
293 if (__old < _S_ssrc_counter_inc) // no stop_source owns *this
294 // No need to register callback if no stop request can be made.
295 // Returning false also means the stop_callback does not share
296 // ownership of this state, but that's not observable.
299 while (!_M_try_lock(__old));
301 __cb->_M_next = _M_head;
304 _M_head->_M_prev = __cb;
311 // Called by ~stop_callback just before destroying *__cb.
312 [[__gnu__::__nonnull__]]
314 _M_remove_callback(_Stop_cb* __cb)
320 _M_head = _M_head->_M_next;
322 _M_head->_M_prev = nullptr;
326 else if (__cb->_M_prev)
328 __cb->_M_prev->_M_next = __cb->_M_next;
330 __cb->_M_next->_M_prev = __cb->_M_prev;
337 // Callback is not in the list, so must have been removed by a call to
340 // Despite appearances there is no data race on _M_requester. The only
341 // write to it happens before the callback is removed from the list,
342 // and removing it from the list happens before this read.
343 if (!(_M_requester == this_thread::get_id()))
345 // Synchronize with completion of callback.
346 __cb->_M_done.acquire();
347 // Safe for ~stop_callback to destroy *__cb now.
351 if (__cb->_M_destroyed)
352 *__cb->_M_destroyed = true;
355 // Try to obtain the lock.
356 // Returns true if the lock is acquired (with memory order acquire).
357 // Otherwise, sets __curval = _M_value.load(__failure) and returns false.
358 // Might fail spuriously, so must be called in a loop.
360 _M_try_lock(value_type& __curval,
361 memory_order __failure = memory_order::acquire) noexcept
363 return _M_do_try_lock(__curval, 0, memory_order::acquire, __failure);
366 // Try to obtain the lock to make a stop request.
367 // Returns true if the lock is acquired and the _S_stop_requested_bit is
368 // set (with memory order acq_rel so that other threads see the request).
369 // Otherwise, sets __curval = _M_value.load(memory_order::acquire) and
371 // Might fail spuriously, so must be called in a loop.
373 _M_try_lock_and_stop(value_type& __curval) noexcept
375 return _M_do_try_lock(__curval, _S_stop_requested_bit,
376 memory_order::acq_rel, memory_order::acquire);
380 _M_do_try_lock(value_type& __curval, value_type __newbits,
381 memory_order __success, memory_order __failure) noexcept
383 if (__curval & _S_locked_bit)
386 __curval = _M_value.load(__failure);
389 __newbits |= _S_locked_bit;
390 return _M_value.compare_exchange_weak(__curval, __curval | __newbits,
391 __success, __failure);
395 struct _Stop_state_ref
397 _Stop_state_ref() = default;
399 [[__gnu__::__access__(__none__, 2)]]
401 _Stop_state_ref(const stop_source&)
402 : _M_ptr(new _Stop_state_t())
405 _Stop_state_ref(const _Stop_state_ref& __other) noexcept
406 : _M_ptr(__other._M_ptr)
409 _M_ptr->_M_add_owner();
412 _Stop_state_ref(_Stop_state_ref&& __other) noexcept
413 : _M_ptr(__other._M_ptr)
415 __other._M_ptr = nullptr;
419 operator=(const _Stop_state_ref& __other) noexcept
421 if (auto __ptr = __other._M_ptr; __ptr != _M_ptr)
424 __ptr->_M_add_owner();
426 _M_ptr->_M_release_ownership();
433 operator=(_Stop_state_ref&& __other) noexcept
435 _Stop_state_ref(std::move(__other)).swap(*this);
442 _M_ptr->_M_release_ownership();
446 swap(_Stop_state_ref& __other) noexcept
447 { std::swap(_M_ptr, __other._M_ptr); }
449 explicit operator bool() const noexcept { return _M_ptr != nullptr; }
451 _Stop_state_t* operator->() const noexcept { return _M_ptr; }
453 #if __cpp_impl_three_way_comparison >= 201907L
455 operator==(const _Stop_state_ref&, const _Stop_state_ref&) = default;
458 operator==(const _Stop_state_ref& __lhs, const _Stop_state_ref& __rhs)
460 { return __lhs._M_ptr == __rhs._M_ptr; }
463 operator!=(const _Stop_state_ref& __lhs, const _Stop_state_ref& __rhs)
465 { return __lhs._M_ptr != __rhs._M_ptr; }
469 _Stop_state_t* _M_ptr = nullptr;
472 _Stop_state_ref _M_state;
475 stop_token(const _Stop_state_ref& __state) noexcept
480 /// A type that allows a stop request to be made.
484 stop_source() : _M_state(*this)
487 explicit stop_source(std::nostopstate_t) noexcept
490 stop_source(const stop_source& __other) noexcept
491 : _M_state(__other._M_state)
494 _M_state->_M_add_ssrc();
497 stop_source(stop_source&&) noexcept = default;
500 operator=(const stop_source& __other) noexcept
502 if (_M_state != __other._M_state)
504 stop_source __sink(std::move(*this));
505 _M_state = __other._M_state;
507 _M_state->_M_add_ssrc();
513 operator=(stop_source&&) noexcept = default;
518 _M_state->_M_sub_ssrc();
523 stop_possible() const noexcept
525 return static_cast<bool>(_M_state);
530 stop_requested() const noexcept
532 return static_cast<bool>(_M_state) && _M_state->_M_stop_requested();
536 request_stop() const noexcept
539 return _M_state->_M_request_stop();
545 get_token() const noexcept
547 return stop_token{_M_state};
551 swap(stop_source& __other) noexcept
553 _M_state.swap(__other._M_state);
558 operator==(const stop_source& __a, const stop_source& __b) noexcept
560 return __a._M_state == __b._M_state;
564 swap(stop_source& __lhs, stop_source& __rhs) noexcept
570 stop_token::_Stop_state_ref _M_state;
573 /// A wrapper for callbacks to be run when a stop request is made.
574 template<typename _Callback>
575 class [[nodiscard]] stop_callback
577 static_assert(is_nothrow_destructible_v<_Callback>);
578 static_assert(is_invocable_v<_Callback>);
581 using callback_type = _Callback;
583 template<typename _Cb,
584 enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
586 stop_callback(const stop_token& __token, _Cb&& __cb)
587 noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
588 : _M_cb(std::forward<_Cb>(__cb))
590 if (auto __state = __token._M_state)
592 if (__state->_M_register_callback(&_M_cb))
593 _M_state.swap(__state);
597 template<typename _Cb,
598 enable_if_t<is_constructible_v<_Callback, _Cb>, int> = 0>
600 stop_callback(stop_token&& __token, _Cb&& __cb)
601 noexcept(is_nothrow_constructible_v<_Callback, _Cb>)
602 : _M_cb(std::forward<_Cb>(__cb))
604 if (auto& __state = __token._M_state)
606 if (__state->_M_register_callback(&_M_cb))
607 _M_state.swap(__state);
615 _M_state->_M_remove_callback(&_M_cb);
619 stop_callback(const stop_callback&) = delete;
620 stop_callback& operator=(const stop_callback&) = delete;
621 stop_callback(stop_callback&&) = delete;
622 stop_callback& operator=(stop_callback&&) = delete;
625 struct _Cb_impl : stop_token::_Stop_cb
627 template<typename _Cb>
630 : _Stop_cb(&_S_execute),
631 _M_cb(std::forward<_Cb>(__cb))
636 [[__gnu__::__nonnull__]]
638 _S_execute(_Stop_cb* __that) noexcept
640 _Callback& __cb = static_cast<_Cb_impl*>(__that)->_M_cb;
641 std::forward<_Callback>(__cb)();
646 stop_token::_Stop_state_ref _M_state;
649 template<typename _Callback>
650 stop_callback(stop_token, _Callback) -> stop_callback<_Callback>;
652 _GLIBCXX_END_NAMESPACE_VERSION
654 #endif // __cplusplus > 201703L
655 #endif // _GLIBCXX_STOP_TOKEN