NAME

std::atomic_flag::wait - std::atomic_flag::wait

Synopsis

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

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(), 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.

Parameters

old - the value to check the atomic_flag'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 another value and back to old
might be missed, and not unblock.

Example

This section is incomplete
Reason: no example

See also

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