std::atomic_flag::wait

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

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

• Compare this->test(order) with that of old.
  • If those are equal, then blocks until *this is notified by notify_one() or notify_all()
  • Otherwise, returns.

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

If order is not std::memory_order_relaxed, std::memory_order_consume, std::memory_order_acquire or std::memory_order_seq_cst

Parameters

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

Notes

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

Due to the ABA problem, transient changes from old to another value and back to old

Example

This section is incomplete Reason: no example

See also

notify_one (C++20)	notifies at least one thread waiting on the atomic object (public member function)
notify_all (C++20)	notifies all threads blocked waiting on the atomic object (public member function)
atomic_flag_notify_one (C++20)	notifies a thread blocked in atomic_flag_wait (function)
atomic_flag_notify_all (C++20)	notifies all threads blocked in atomic_flag_wait (function)