Waiter

    const Waiter = struct {
        node: std.DoublyLinkedList.Node,
        address: usize,
        tid: ParkTid,
        /// `thread_status.cancelation` is `.parked` while the thread is waiting. The single thread
        /// which atomically updates it (to `.none` or `.canceling`) is responsible for:
        ///
        /// * Removing the `Waiter` from `Bucket.waiters`
        /// * Decrementing `Bucket.num_waiters`
        /// * Unparking the thread (*after* the above, so that the `Waiter` does not go out of scope
        ///   while it is still in the `Bucket`).
        thread_status: *std.atomic.Value(Thread.Status),
        unpark_flag: if (need_unpark_flag) *UnparkFlag else void,
    }