std::atomic_flag::wait

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Concurrency support library

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Atomic types
atomic (C++11)
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atomic_flag (C++11)
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atomic_loadatomic_load_explicit (C++11)(C++11)
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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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std::atomic_flag

Member functions
atomic_flag::atomic_flag
atomic_flag::operator=
atomic_flag::clear
atomic_flag::test_and_set
atomic_flag::test (C++20)
atomic_flag::wait (C++20)
atomic_flag::notify_one (C++20)
atomic_flag::notify_all (C++20)

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void wait(bool old,std::memory_order order= std::memory_order_seq_cst)constnoexcept;	(1)	(since C++20) (constexpr since C++26)
void wait(bool old, std::memory_order order= std::memory_order_seq_cst)constvolatilenoexcept;	(2)	(since C++20)

Performs atomic waiting operations. Behaves as if it repeatedly performs the following steps:

Comparethis->test(order) with that ofold.
- If those are equal, then blocks until*this is notified bynotify_one() ornotify_all(), or the thread is unblocked spuriously.
- Otherwise, returns.

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

Iforder is notstd::memory_order_relaxed,std::memory_order_consume,std::memory_order_acquire orstd::memory_order_seq_cst, the behavior is undefined.

[edit]Parameters

old	-	the value to check the`atomic_flag`'s object no longer contains
order	-	memory order constraints to enforce

[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)[edit]
notify_all (C++20)	notifies all threads blocked waiting on the atomic object (public member function)[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]