void atomic_flag_wait( const atomic_flag* object, bool old ) noexcept;
(1) (since C++20)void atomic_flag_wait( const volatile atomic_flag* object,
bool old ) noexcept;
Performs atomic waiting operations.
Compares object->test(std::memory_order_seq_cst) or object->test(order) with old, and if they are equal then blocks until *object is notified by std::atomic_flag::notify_one() or std::atomic_flag::notify_all() (or the thread is unblocked spuriously). This is repeated until the values compare unequal.
3,4) The memory synchronization order is order.
These functions are guaranteed to return only if value has changed, even if underlying implementation unblocks spuriously.
[edit] Parameters object - pointer to the atomic flag to check and wait on old - the value to check the atomic flag no longer contains order - the memory synchronization ordering [edit] Return value(none)
[edit] NotesThis 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.
[edit] Example [edit] See also notifies at least one thread waiting on the atomic objectstd::atomic_flag) [edit] notifies all threads blocked waiting on the atomic object
std::atomic_flag) [edit] notifies a thread blocked in atomic_flag_wait
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