Template:cpp/atomic/atomic/wait

		(since C++20)
void wait( T old,            std::memory_order = std::memory_order::seq_cst ) const noexcept;
void wait( T old,            std::memory_order = std::memory_order::seq_cst ) const volatile noexcept;

Compares the value representation of the this->load(order) with that of old, and if those are bitwise equal then blocks until the one of this->load(order) changes or *this is notified by notify_one() or notify_all(). These functions are allowed to unblock spuriously, i.e. return due to reasons other than value change or notification.

Parameters

old	-	the value to check the 's object no longer contains
order	-	the memory synchronization ordering for this operation: must not be std::memory_order::release or std::memory_order::acq_rel

Return value

(none)

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 something else and back to old might be missed, and not unblock.

See also

notify_one (C++20)	notifies at least one thread waiting on the atomic object (public member function of Template:cpp/atomic//title)
notify_all (C++20)	notifies all threads blocked waiting on the atomic object (public member function of Template:cpp/atomic//title)
atomic_notify_one (C++20)	notifies a thread blocked in atomic_wait (function template)
atomic_notify_all (C++20)	notifies all threads blocked in atomic_wait (function template)