std::atomic_flag_wait,std::atomic_flag_wait_explicit

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Atomic types
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atomic_flag (C++11)
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atomic_storeatomic_store_explicit (C++11)(C++11)
atomic_loadatomic_load_explicit (C++11)(C++11)
atomic_exchangeatomic_exchange_explicit (C++11)(C++11)
atomic_compare_exchange_weakatomic_compare_exchange_weak_explicitatomic_compare_exchange_strongatomic_compare_exchange_strong_explicit (C++11)(C++11)(C++11)(C++11)
atomic_fetch_addatomic_fetch_add_explicit (C++11)(C++11)
atomic_fetch_subatomic_fetch_sub_explicit (C++11)(C++11)
atomic_fetch_andatomic_fetch_and_explicit (C++11)(C++11)
atomic_fetch_oratomic_fetch_or_explicit (C++11)(C++11)
atomic_fetch_xoratomic_fetch_xor_explicit (C++11)(C++11)
atomic_fetch_maxatomic_fetch_max_explicit (C++26)(C++26)
atomic_fetch_minatomic_fetch_min_explicit (C++26)(C++26)
atomic_is_lock_free (C++11)
atomic_waitatomic_wait_explicit (C++20)(C++20)
atomic_notify_one (C++20)
atomic_notify_all (C++20)
Free functions for atomic flags
atomic_flag_test_and_setatomic_flag_test_and_set_explicit (C++11)(C++11)
atomic_flag_clearatomic_flag_clear_explicit (C++11)(C++11)
atomic_flag_testatomic_flag_test_explicit (C++20)(C++20)
atomic_flag_waitatomic_flag_wait_explicit (C++20)(C++20)
atomic_flag_notify_one (C++20)
atomic_flag_notify_all (C++20)

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Defined in header`<atomic>`
void atomic_flag_wait(const atomic_flag* object,bool old)noexcept;	(1)	(since C++20)
void atomic_flag_wait(constvolatile atomic_flag* object, bool old)noexcept;	(2)	(since C++20)
void atomic_flag_wait_explicit(const atomic_flag* object, bool old,std::memory_order order)noexcept;	(3)	(since C++20)
void atomic_flag_wait_explicit(constvolatile atomic_flag* object, bool old,std::memory_order order)noexcept;	(4)	(since C++20)

Performs atomic waiting operations.

Comparesobject->test(std::memory_order_seq_cst) orobject->test(order) withold, and if they are equal then blocks until*object is notified bystd::atomic_flag::notify_one() orstd::atomic_flag::notify_all() (or the thread is unblocked spuriously). This is repeated until the values compare unequal.

1,2) The memory synchronization order isstd::memory_order_seq_cst.

3,4) The memory synchronization order isorder.

Iforder is one ofstd::memory_order_release andstd::memory_order_acq_rel, the behavior is undefined.

These functions are guaranteed to return only if value has changed, even if underlying implementation unblocks spuriously.

[edit]Parameters

object	-	pointer to the atomic flag to check and wait on
old	-	the value to check the atomic flag no longer contains
order	-	the memory synchronization ordering

[edit]Return value

(none)

[edit]Notes

This form of change-detection is often more efficient than simple polling or pure spinlocks.

Due to theABA problem, transient changes fromold to another value and back toold might be missed, and not unblock.

[edit]Example

This section is incomplete
Reason: no example

[edit]See also

notify_one (C++20)	notifies at least one thread waiting on the atomic object (public member function of`std::atomic_flag`)[edit]
notify_all (C++20)	notifies all threads blocked waiting on the atomic object (public member function of`std::atomic_flag`)[edit]
atomic_flag_notify_one (C++20)	notifies a thread blocked in atomic_flag_wait (function)[edit]
atomic_flag_notify_all (C++20)	notifies all threads blocked in atomic_flag_wait (function)[edit]