2 //===----------------------------------------------------------------------===//
4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
5 // See https://llvm.org/LICENSE.txt for license information.
6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
8 //===----------------------------------------------------------------------===//
10 #ifndef _LIBCPP_ATOMIC
11 #define _LIBCPP_ATOMIC
19 // feature test macro [version.syn]
21 #define __cpp_lib_atomic_is_always_lock_free
22 #define __cpp_lib_atomic_flag_test
23 #define __cpp_lib_atomic_lock_free_type_aliases
24 #define __cpp_lib_atomic_wait
26 // order and consistency
28 enum memory_order: unspecified // enum class in C++20
31 consume, // load-consume
32 acquire, // load-acquire
33 release, // store-release
34 acq_rel, // store-release load-acquire
35 seq_cst // store-release load-acquire
38 inline constexpr auto memory_order_relaxed = memory_order::relaxed;
39 inline constexpr auto memory_order_consume = memory_order::consume;
40 inline constexpr auto memory_order_acquire = memory_order::acquire;
41 inline constexpr auto memory_order_release = memory_order::release;
42 inline constexpr auto memory_order_acq_rel = memory_order::acq_rel;
43 inline constexpr auto memory_order_seq_cst = memory_order::seq_cst;
45 template <class T> T kill_dependency(T y) noexcept;
49 #define ATOMIC_BOOL_LOCK_FREE unspecified
50 #define ATOMIC_CHAR_LOCK_FREE unspecified
51 #define ATOMIC_CHAR8_T_LOCK_FREE unspecified // C++20
52 #define ATOMIC_CHAR16_T_LOCK_FREE unspecified
53 #define ATOMIC_CHAR32_T_LOCK_FREE unspecified
54 #define ATOMIC_WCHAR_T_LOCK_FREE unspecified
55 #define ATOMIC_SHORT_LOCK_FREE unspecified
56 #define ATOMIC_INT_LOCK_FREE unspecified
57 #define ATOMIC_LONG_LOCK_FREE unspecified
58 #define ATOMIC_LLONG_LOCK_FREE unspecified
59 #define ATOMIC_POINTER_LOCK_FREE unspecified
66 static constexpr bool is_always_lock_free;
67 bool is_lock_free() const volatile noexcept;
68 bool is_lock_free() const noexcept;
70 atomic() noexcept = default; // until C++20
71 constexpr atomic() noexcept(is_nothrow_default_constructible_v<T>); // since C++20
72 constexpr atomic(T desr) noexcept;
73 atomic(const atomic&) = delete;
74 atomic& operator=(const atomic&) = delete;
75 atomic& operator=(const atomic&) volatile = delete;
77 T load(memory_order m = memory_order_seq_cst) const volatile noexcept;
78 T load(memory_order m = memory_order_seq_cst) const noexcept;
79 operator T() const volatile noexcept;
80 operator T() const noexcept;
81 void store(T desr, memory_order m = memory_order_seq_cst) volatile noexcept;
82 void store(T desr, memory_order m = memory_order_seq_cst) noexcept;
83 T operator=(T) volatile noexcept;
84 T operator=(T) noexcept;
86 T exchange(T desr, memory_order m = memory_order_seq_cst) volatile noexcept;
87 T exchange(T desr, memory_order m = memory_order_seq_cst) noexcept;
88 bool compare_exchange_weak(T& expc, T desr,
89 memory_order s, memory_order f) volatile noexcept;
90 bool compare_exchange_weak(T& expc, T desr, memory_order s, memory_order f) noexcept;
91 bool compare_exchange_strong(T& expc, T desr,
92 memory_order s, memory_order f) volatile noexcept;
93 bool compare_exchange_strong(T& expc, T desr,
94 memory_order s, memory_order f) noexcept;
95 bool compare_exchange_weak(T& expc, T desr,
96 memory_order m = memory_order_seq_cst) volatile noexcept;
97 bool compare_exchange_weak(T& expc, T desr,
98 memory_order m = memory_order_seq_cst) noexcept;
99 bool compare_exchange_strong(T& expc, T desr,
100 memory_order m = memory_order_seq_cst) volatile noexcept;
101 bool compare_exchange_strong(T& expc, T desr,
102 memory_order m = memory_order_seq_cst) noexcept;
104 void wait(T, memory_order = memory_order::seq_cst) const volatile noexcept;
105 void wait(T, memory_order = memory_order::seq_cst) const noexcept;
106 void notify_one() volatile noexcept;
107 void notify_one() noexcept;
108 void notify_all() volatile noexcept;
109 void notify_all() noexcept;
113 struct atomic<integral>
115 using value_type = integral;
116 using difference_type = value_type;
118 static constexpr bool is_always_lock_free;
119 bool is_lock_free() const volatile noexcept;
120 bool is_lock_free() const noexcept;
122 atomic() noexcept = default;
123 constexpr atomic(integral desr) noexcept;
124 atomic(const atomic&) = delete;
125 atomic& operator=(const atomic&) = delete;
126 atomic& operator=(const atomic&) volatile = delete;
128 integral load(memory_order m = memory_order_seq_cst) const volatile noexcept;
129 integral load(memory_order m = memory_order_seq_cst) const noexcept;
130 operator integral() const volatile noexcept;
131 operator integral() const noexcept;
132 void store(integral desr, memory_order m = memory_order_seq_cst) volatile noexcept;
133 void store(integral desr, memory_order m = memory_order_seq_cst) noexcept;
134 integral operator=(integral desr) volatile noexcept;
135 integral operator=(integral desr) noexcept;
137 integral exchange(integral desr,
138 memory_order m = memory_order_seq_cst) volatile noexcept;
139 integral exchange(integral desr, memory_order m = memory_order_seq_cst) noexcept;
140 bool compare_exchange_weak(integral& expc, integral desr,
141 memory_order s, memory_order f) volatile noexcept;
142 bool compare_exchange_weak(integral& expc, integral desr,
143 memory_order s, memory_order f) noexcept;
144 bool compare_exchange_strong(integral& expc, integral desr,
145 memory_order s, memory_order f) volatile noexcept;
146 bool compare_exchange_strong(integral& expc, integral desr,
147 memory_order s, memory_order f) noexcept;
148 bool compare_exchange_weak(integral& expc, integral desr,
149 memory_order m = memory_order_seq_cst) volatile noexcept;
150 bool compare_exchange_weak(integral& expc, integral desr,
151 memory_order m = memory_order_seq_cst) noexcept;
152 bool compare_exchange_strong(integral& expc, integral desr,
153 memory_order m = memory_order_seq_cst) volatile noexcept;
154 bool compare_exchange_strong(integral& expc, integral desr,
155 memory_order m = memory_order_seq_cst) noexcept;
157 integral fetch_add(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
158 integral fetch_add(integral op, memory_order m = memory_order_seq_cst) noexcept;
159 integral fetch_sub(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
160 integral fetch_sub(integral op, memory_order m = memory_order_seq_cst) noexcept;
161 integral fetch_and(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
162 integral fetch_and(integral op, memory_order m = memory_order_seq_cst) noexcept;
163 integral fetch_or(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
164 integral fetch_or(integral op, memory_order m = memory_order_seq_cst) noexcept;
165 integral fetch_xor(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
166 integral fetch_xor(integral op, memory_order m = memory_order_seq_cst) noexcept;
168 integral operator++(int) volatile noexcept;
169 integral operator++(int) noexcept;
170 integral operator--(int) volatile noexcept;
171 integral operator--(int) noexcept;
172 integral operator++() volatile noexcept;
173 integral operator++() noexcept;
174 integral operator--() volatile noexcept;
175 integral operator--() noexcept;
176 integral operator+=(integral op) volatile noexcept;
177 integral operator+=(integral op) noexcept;
178 integral operator-=(integral op) volatile noexcept;
179 integral operator-=(integral op) noexcept;
180 integral operator&=(integral op) volatile noexcept;
181 integral operator&=(integral op) noexcept;
182 integral operator|=(integral op) volatile noexcept;
183 integral operator|=(integral op) noexcept;
184 integral operator^=(integral op) volatile noexcept;
185 integral operator^=(integral op) noexcept;
187 void wait(integral, memory_order = memory_order::seq_cst) const volatile noexcept;
188 void wait(integral, memory_order = memory_order::seq_cst) const noexcept;
189 void notify_one() volatile noexcept;
190 void notify_one() noexcept;
191 void notify_all() volatile noexcept;
192 void notify_all() noexcept;
198 using value_type = T*;
199 using difference_type = ptrdiff_t;
201 static constexpr bool is_always_lock_free;
202 bool is_lock_free() const volatile noexcept;
203 bool is_lock_free() const noexcept;
205 atomic() noexcept = default; // until C++20
206 constexpr atomic() noexcept; // since C++20
207 constexpr atomic(T* desr) noexcept;
208 atomic(const atomic&) = delete;
209 atomic& operator=(const atomic&) = delete;
210 atomic& operator=(const atomic&) volatile = delete;
212 T* load(memory_order m = memory_order_seq_cst) const volatile noexcept;
213 T* load(memory_order m = memory_order_seq_cst) const noexcept;
214 operator T*() const volatile noexcept;
215 operator T*() const noexcept;
216 void store(T* desr, memory_order m = memory_order_seq_cst) volatile noexcept;
217 void store(T* desr, memory_order m = memory_order_seq_cst) noexcept;
218 T* operator=(T*) volatile noexcept;
219 T* operator=(T*) noexcept;
221 T* exchange(T* desr, memory_order m = memory_order_seq_cst) volatile noexcept;
222 T* exchange(T* desr, memory_order m = memory_order_seq_cst) noexcept;
223 bool compare_exchange_weak(T*& expc, T* desr,
224 memory_order s, memory_order f) volatile noexcept;
225 bool compare_exchange_weak(T*& expc, T* desr,
226 memory_order s, memory_order f) noexcept;
227 bool compare_exchange_strong(T*& expc, T* desr,
228 memory_order s, memory_order f) volatile noexcept;
229 bool compare_exchange_strong(T*& expc, T* desr,
230 memory_order s, memory_order f) noexcept;
231 bool compare_exchange_weak(T*& expc, T* desr,
232 memory_order m = memory_order_seq_cst) volatile noexcept;
233 bool compare_exchange_weak(T*& expc, T* desr,
234 memory_order m = memory_order_seq_cst) noexcept;
235 bool compare_exchange_strong(T*& expc, T* desr,
236 memory_order m = memory_order_seq_cst) volatile noexcept;
237 bool compare_exchange_strong(T*& expc, T* desr,
238 memory_order m = memory_order_seq_cst) noexcept;
239 T* fetch_add(ptrdiff_t op, memory_order m = memory_order_seq_cst) volatile noexcept;
240 T* fetch_add(ptrdiff_t op, memory_order m = memory_order_seq_cst) noexcept;
241 T* fetch_sub(ptrdiff_t op, memory_order m = memory_order_seq_cst) volatile noexcept;
242 T* fetch_sub(ptrdiff_t op, memory_order m = memory_order_seq_cst) noexcept;
244 T* operator++(int) volatile noexcept;
245 T* operator++(int) noexcept;
246 T* operator--(int) volatile noexcept;
247 T* operator--(int) noexcept;
248 T* operator++() volatile noexcept;
249 T* operator++() noexcept;
250 T* operator--() volatile noexcept;
251 T* operator--() noexcept;
252 T* operator+=(ptrdiff_t op) volatile noexcept;
253 T* operator+=(ptrdiff_t op) noexcept;
254 T* operator-=(ptrdiff_t op) volatile noexcept;
255 T* operator-=(ptrdiff_t op) noexcept;
257 void wait(T*, memory_order = memory_order::seq_cst) const volatile noexcept;
258 void wait(T*, memory_order = memory_order::seq_cst) const noexcept;
259 void notify_one() volatile noexcept;
260 void notify_one() noexcept;
261 void notify_all() volatile noexcept;
262 void notify_all() noexcept;
266 // [atomics.nonmembers], non-member functions
268 bool atomic_is_lock_free(const volatile atomic<T>*) noexcept;
270 bool atomic_is_lock_free(const atomic<T>*) noexcept;
272 void atomic_store(volatile atomic<T>*, atomic<T>::value_type) noexcept;
274 void atomic_store(atomic<T>*, atomic<T>::value_type) noexcept;
276 void atomic_store_explicit(volatile atomic<T>*, atomic<T>::value_type,
277 memory_order) noexcept;
279 void atomic_store_explicit(atomic<T>*, atomic<T>::value_type,
280 memory_order) noexcept;
282 T atomic_load(const volatile atomic<T>*) noexcept;
284 T atomic_load(const atomic<T>*) noexcept;
286 T atomic_load_explicit(const volatile atomic<T>*, memory_order) noexcept;
288 T atomic_load_explicit(const atomic<T>*, memory_order) noexcept;
290 T atomic_exchange(volatile atomic<T>*, atomic<T>::value_type) noexcept;
292 T atomic_exchange(atomic<T>*, atomic<T>::value_type) noexcept;
294 T atomic_exchange_explicit(volatile atomic<T>*, atomic<T>::value_type,
295 memory_order) noexcept;
297 T atomic_exchange_explicit(atomic<T>*, atomic<T>::value_type,
298 memory_order) noexcept;
300 bool atomic_compare_exchange_weak(volatile atomic<T>*, atomic<T>::value_type*,
301 atomic<T>::value_type) noexcept;
303 bool atomic_compare_exchange_weak(atomic<T>*, atomic<T>::value_type*,
304 atomic<T>::value_type) noexcept;
306 bool atomic_compare_exchange_strong(volatile atomic<T>*, atomic<T>::value_type*,
307 atomic<T>::value_type) noexcept;
309 bool atomic_compare_exchange_strong(atomic<T>*, atomic<T>::value_type*,
310 atomic<T>::value_type) noexcept;
312 bool atomic_compare_exchange_weak_explicit(volatile atomic<T>*, atomic<T>::value_type*,
313 atomic<T>::value_type,
314 memory_order, memory_order) noexcept;
316 bool atomic_compare_exchange_weak_explicit(atomic<T>*, atomic<T>::value_type*,
317 atomic<T>::value_type,
318 memory_order, memory_order) noexcept;
320 bool atomic_compare_exchange_strong_explicit(volatile atomic<T>*, atomic<T>::value_type*,
321 atomic<T>::value_type,
322 memory_order, memory_order) noexcept;
324 bool atomic_compare_exchange_strong_explicit(atomic<T>*, atomic<T>::value_type*,
325 atomic<T>::value_type,
326 memory_order, memory_order) noexcept;
329 T atomic_fetch_add(volatile atomic<T>*, atomic<T>::difference_type) noexcept;
331 T atomic_fetch_add(atomic<T>*, atomic<T>::difference_type) noexcept;
333 T atomic_fetch_add_explicit(volatile atomic<T>*, atomic<T>::difference_type,
334 memory_order) noexcept;
336 T atomic_fetch_add_explicit(atomic<T>*, atomic<T>::difference_type,
337 memory_order) noexcept;
339 T atomic_fetch_sub(volatile atomic<T>*, atomic<T>::difference_type) noexcept;
341 T atomic_fetch_sub(atomic<T>*, atomic<T>::difference_type) noexcept;
343 T atomic_fetch_sub_explicit(volatile atomic<T>*, atomic<T>::difference_type,
344 memory_order) noexcept;
346 T atomic_fetch_sub_explicit(atomic<T>*, atomic<T>::difference_type,
347 memory_order) noexcept;
349 T atomic_fetch_and(volatile atomic<T>*, atomic<T>::value_type) noexcept;
351 T atomic_fetch_and(atomic<T>*, atomic<T>::value_type) noexcept;
353 T atomic_fetch_and_explicit(volatile atomic<T>*, atomic<T>::value_type,
354 memory_order) noexcept;
356 T atomic_fetch_and_explicit(atomic<T>*, atomic<T>::value_type,
357 memory_order) noexcept;
359 T atomic_fetch_or(volatile atomic<T>*, atomic<T>::value_type) noexcept;
361 T atomic_fetch_or(atomic<T>*, atomic<T>::value_type) noexcept;
363 T atomic_fetch_or_explicit(volatile atomic<T>*, atomic<T>::value_type,
364 memory_order) noexcept;
366 T atomic_fetch_or_explicit(atomic<T>*, atomic<T>::value_type,
367 memory_order) noexcept;
369 T atomic_fetch_xor(volatile atomic<T>*, atomic<T>::value_type) noexcept;
371 T atomic_fetch_xor(atomic<T>*, atomic<T>::value_type) noexcept;
373 T atomic_fetch_xor_explicit(volatile atomic<T>*, atomic<T>::value_type,
374 memory_order) noexcept;
376 T atomic_fetch_xor_explicit(atomic<T>*, atomic<T>::value_type,
377 memory_order) noexcept;
380 void atomic_wait(const volatile atomic<T>*, atomic<T>::value_type) noexcept;
382 void atomic_wait(const atomic<T>*, atomic<T>::value_type) noexcept;
384 void atomic_wait_explicit(const volatile atomic<T>*, atomic<T>::value_type,
385 memory_order) noexcept;
387 void atomic_wait_explicit(const atomic<T>*, atomic<T>::value_type,
388 memory_order) noexcept;
390 void atomic_notify_one(volatile atomic<T>*) noexcept;
392 void atomic_notify_one(atomic<T>*) noexcept;
394 void atomic_notify_all(volatile atomic<T>*) noexcept;
396 void atomic_notify_all(atomic<T>*) noexcept;
398 // Atomics for standard typedef types
400 typedef atomic<bool> atomic_bool;
401 typedef atomic<char> atomic_char;
402 typedef atomic<signed char> atomic_schar;
403 typedef atomic<unsigned char> atomic_uchar;
404 typedef atomic<short> atomic_short;
405 typedef atomic<unsigned short> atomic_ushort;
406 typedef atomic<int> atomic_int;
407 typedef atomic<unsigned int> atomic_uint;
408 typedef atomic<long> atomic_long;
409 typedef atomic<unsigned long> atomic_ulong;
410 typedef atomic<long long> atomic_llong;
411 typedef atomic<unsigned long long> atomic_ullong;
412 typedef atomic<char8_t> atomic_char8_t; // C++20
413 typedef atomic<char16_t> atomic_char16_t;
414 typedef atomic<char32_t> atomic_char32_t;
415 typedef atomic<wchar_t> atomic_wchar_t;
417 typedef atomic<int_least8_t> atomic_int_least8_t;
418 typedef atomic<uint_least8_t> atomic_uint_least8_t;
419 typedef atomic<int_least16_t> atomic_int_least16_t;
420 typedef atomic<uint_least16_t> atomic_uint_least16_t;
421 typedef atomic<int_least32_t> atomic_int_least32_t;
422 typedef atomic<uint_least32_t> atomic_uint_least32_t;
423 typedef atomic<int_least64_t> atomic_int_least64_t;
424 typedef atomic<uint_least64_t> atomic_uint_least64_t;
426 typedef atomic<int_fast8_t> atomic_int_fast8_t;
427 typedef atomic<uint_fast8_t> atomic_uint_fast8_t;
428 typedef atomic<int_fast16_t> atomic_int_fast16_t;
429 typedef atomic<uint_fast16_t> atomic_uint_fast16_t;
430 typedef atomic<int_fast32_t> atomic_int_fast32_t;
431 typedef atomic<uint_fast32_t> atomic_uint_fast32_t;
432 typedef atomic<int_fast64_t> atomic_int_fast64_t;
433 typedef atomic<uint_fast64_t> atomic_uint_fast64_t;
435 typedef atomic<int8_t> atomic_int8_t;
436 typedef atomic<uint8_t> atomic_uint8_t;
437 typedef atomic<int16_t> atomic_int16_t;
438 typedef atomic<uint16_t> atomic_uint16_t;
439 typedef atomic<int32_t> atomic_int32_t;
440 typedef atomic<uint32_t> atomic_uint32_t;
441 typedef atomic<int64_t> atomic_int64_t;
442 typedef atomic<uint64_t> atomic_uint64_t;
444 typedef atomic<intptr_t> atomic_intptr_t;
445 typedef atomic<uintptr_t> atomic_uintptr_t;
446 typedef atomic<size_t> atomic_size_t;
447 typedef atomic<ptrdiff_t> atomic_ptrdiff_t;
448 typedef atomic<intmax_t> atomic_intmax_t;
449 typedef atomic<uintmax_t> atomic_uintmax_t;
451 // flag type and operations
453 typedef struct atomic_flag
455 atomic_flag() noexcept = default; // until C++20
456 constexpr atomic_flag() noexcept; // since C++20
457 atomic_flag(const atomic_flag&) = delete;
458 atomic_flag& operator=(const atomic_flag&) = delete;
459 atomic_flag& operator=(const atomic_flag&) volatile = delete;
461 bool test(memory_order m = memory_order_seq_cst) volatile noexcept;
462 bool test(memory_order m = memory_order_seq_cst) noexcept;
463 bool test_and_set(memory_order m = memory_order_seq_cst) volatile noexcept;
464 bool test_and_set(memory_order m = memory_order_seq_cst) noexcept;
465 void clear(memory_order m = memory_order_seq_cst) volatile noexcept;
466 void clear(memory_order m = memory_order_seq_cst) noexcept;
468 void wait(bool, memory_order = memory_order::seq_cst) const volatile noexcept;
469 void wait(bool, memory_order = memory_order::seq_cst) const noexcept;
470 void notify_one() volatile noexcept;
471 void notify_one() noexcept;
472 void notify_all() volatile noexcept;
473 void notify_all() noexcept;
476 bool atomic_flag_test(volatile atomic_flag* obj) noexcept;
477 bool atomic_flag_test(atomic_flag* obj) noexcept;
478 bool atomic_flag_test_explicit(volatile atomic_flag* obj,
479 memory_order m) noexcept;
480 bool atomic_flag_test_explicit(atomic_flag* obj, memory_order m) noexcept;
481 bool atomic_flag_test_and_set(volatile atomic_flag* obj) noexcept;
482 bool atomic_flag_test_and_set(atomic_flag* obj) noexcept;
483 bool atomic_flag_test_and_set_explicit(volatile atomic_flag* obj,
484 memory_order m) noexcept;
485 bool atomic_flag_test_and_set_explicit(atomic_flag* obj, memory_order m) noexcept;
486 void atomic_flag_clear(volatile atomic_flag* obj) noexcept;
487 void atomic_flag_clear(atomic_flag* obj) noexcept;
488 void atomic_flag_clear_explicit(volatile atomic_flag* obj, memory_order m) noexcept;
489 void atomic_flag_clear_explicit(atomic_flag* obj, memory_order m) noexcept;
491 void atomic_wait(const volatile atomic_flag* obj, T old) noexcept;
492 void atomic_wait(const atomic_flag* obj, T old) noexcept;
493 void atomic_wait_explicit(const volatile atomic_flag* obj, T old, memory_order m) noexcept;
494 void atomic_wait_explicit(const atomic_flag* obj, T old, memory_order m) noexcept;
495 void atomic_one(volatile atomic_flag* obj) noexcept;
496 void atomic_one(atomic_flag* obj) noexcept;
497 void atomic_all(volatile atomic_flag* obj) noexcept;
498 void atomic_all(atomic_flag* obj) noexcept;
502 void atomic_thread_fence(memory_order m) noexcept;
503 void atomic_signal_fence(memory_order m) noexcept;
508 void atomic_init(volatile atomic<T>* obj, atomic<T>::value_type desr) noexcept;
511 void atomic_init(atomic<T>* obj, atomic<T>::value_type desr) noexcept;
513 #define ATOMIC_VAR_INIT(value) see below
515 #define ATOMIC_FLAG_INIT see below
521 #include <__assert> // all public C++ headers provide the assertion handler
522 #include <__atomic/aliases.h>
523 #include <__atomic/atomic.h>
524 #include <__atomic/atomic_base.h>
525 #include <__atomic/atomic_flag.h>
526 #include <__atomic/atomic_init.h>
527 #include <__atomic/atomic_lock_free.h>
528 #include <__atomic/atomic_sync.h>
529 #include <__atomic/check_memory_order.h>
530 #include <__atomic/contention_t.h>
531 #include <__atomic/cxx_atomic_impl.h>
532 #include <__atomic/fence.h>
533 #include <__atomic/is_always_lock_free.h>
534 #include <__atomic/kill_dependency.h>
535 #include <__atomic/memory_order.h>
539 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
540 # pragma GCC system_header
543 #ifdef _LIBCPP_HAS_NO_ATOMIC_HEADER
544 # error <atomic> is not implemented
547 #ifdef kill_dependency
548 # error <atomic> is incompatible with <stdatomic.h> before C++23. Please compile with -std=c++23.
551 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
555 # include <type_traits>
558 #endif // _LIBCPP_ATOMIC