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// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License in the LICENSE-APACHE file or at:
//     https://www.apache.org/licenses/LICENSE-2.0

//! Event handling: updates

#![allow(clippy::new_without_default)]

use std::sync::atomic::{AtomicU32, Ordering::Relaxed};

/// An update identifier
///
/// Used to identify the origin of an [`Event::Update`](crate::event::Event::Update).
#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
#[must_use]
pub struct UpdateId(u32);

impl UpdateId {
    /// Zero: used when a unique identifier isn't required
    pub const ZERO: UpdateId = UpdateId(0);

    /// Issue a new [`UpdateId`]
    ///
    /// A total of 2<sup>32</sup> - 1 update handles are available.
    /// Attempting to issue 2<sup>32</sup> handles will result in a panic.
    pub fn new() -> UpdateId {
        static COUNT: AtomicU32 = AtomicU32::new(0);

        loop {
            let c = COUNT.load(Relaxed);
            let h = c.wrapping_add(1);
            assert!(
                h != 0,
                "UpdateId::new: all available handles have been issued"
            );
            if COUNT.compare_exchange(c, h, Relaxed, Relaxed).is_ok() {
                break UpdateId(h);
            }
        }
    }
}