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 not std::memory_order_relaxed, std::memory_order_consume, std::memory_order_acquire or std::memory_order_seq_cst, the behavior is undefined.

Parameters

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

See also