NAME¶

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

Synopsis¶

void wait( bool old, std::memory_order order =
std::memory_order::seq_cst ) const (1) (since C++20)
noexcept;
void wait( bool old, std::memory_order order =
std::memory_order::seq_cst ) const (2) (since C++20)
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.

If order is one of std::memory_order::release and std::memory_order::acq_rel, the
behavior is undefined.

Parameters¶

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

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)

Category:¶

* Todo no example