NAME¶

std::atomic_ref::wait - std::atomic_ref::wait

Synopsis¶

void wait( T old,
std::memory_order order = std::memory_order::seq_cst ) const
noexcept; (since C++20)
void wait( T 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 the value representation of this->load(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_ref'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.

The comparison is bitwise (similar to std::memcmp); no comparison operator is used.
Padding bits that never participate in an object's value representation are ignored.

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_notify_one notifies a thread blocked in atomic_wait
(C++20) (function template)
atomic_notify_all notifies all threads blocked in atomic_wait
(C++20) (function template)