bevy_ecs/world/
identifier.rs

1use crate::system::{ExclusiveSystemParam, SystemMeta};
2use crate::{
3    component::Tick,
4    storage::SparseSetIndex,
5    system::{ReadOnlySystemParam, SystemParam},
6    world::{FromWorld, World},
7};
8use std::sync::atomic::{AtomicUsize, Ordering};
9
10use super::unsafe_world_cell::UnsafeWorldCell;
11
12#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
13// We use usize here because that is the largest `Atomic` we want to require
14/// A unique identifier for a [`World`].
15///
16/// The trait [`FromWorld`] is implemented for this type, which returns the
17/// ID of the world passed to [`FromWorld::from_world`].
18// Note that this *is* used by external crates as well as for internal safety checks
19pub struct WorldId(usize);
20
21/// The next [`WorldId`].
22static MAX_WORLD_ID: AtomicUsize = AtomicUsize::new(0);
23
24impl WorldId {
25    /// Create a new, unique [`WorldId`]. Returns [`None`] if the supply of unique
26    /// [`WorldId`]s has been exhausted
27    ///
28    /// Please note that the [`WorldId`]s created from this method are unique across
29    /// time - if a given [`WorldId`] is [`Drop`]ped its value still cannot be reused
30    pub fn new() -> Option<Self> {
31        MAX_WORLD_ID
32            // We use `Relaxed` here since this atomic only needs to be consistent with itself
33            .fetch_update(Ordering::Relaxed, Ordering::Relaxed, |val| {
34                val.checked_add(1)
35            })
36            .map(WorldId)
37            .ok()
38    }
39}
40
41impl FromWorld for WorldId {
42    #[inline]
43    fn from_world(world: &mut World) -> Self {
44        world.id()
45    }
46}
47
48// SAFETY: No world data is accessed.
49unsafe impl ReadOnlySystemParam for WorldId {}
50
51// SAFETY: No world data is accessed.
52unsafe impl SystemParam for WorldId {
53    type State = ();
54
55    type Item<'world, 'state> = WorldId;
56
57    fn init_state(_: &mut World, _: &mut crate::system::SystemMeta) -> Self::State {}
58
59    unsafe fn get_param<'world, 'state>(
60        _: &'state mut Self::State,
61        _: &crate::system::SystemMeta,
62        world: UnsafeWorldCell<'world>,
63        _: Tick,
64    ) -> Self::Item<'world, 'state> {
65        world.id()
66    }
67}
68
69impl ExclusiveSystemParam for WorldId {
70    type State = WorldId;
71    type Item<'s> = WorldId;
72
73    fn init(world: &mut World, _system_meta: &mut SystemMeta) -> Self::State {
74        world.id()
75    }
76
77    fn get_param<'s>(state: &'s mut Self::State, _system_meta: &SystemMeta) -> Self::Item<'s> {
78        *state
79    }
80}
81
82impl SparseSetIndex for WorldId {
83    #[inline]
84    fn sparse_set_index(&self) -> usize {
85        self.0
86    }
87
88    #[inline]
89    fn get_sparse_set_index(value: usize) -> Self {
90        Self(value)
91    }
92}
93
94#[cfg(test)]
95mod tests {
96    use super::*;
97
98    #[test]
99    fn world_ids_unique() {
100        let ids = std::iter::repeat_with(WorldId::new)
101            .take(50)
102            .map(Option::unwrap)
103            .collect::<Vec<_>>();
104        for (i, &id1) in ids.iter().enumerate() {
105            // For the first element, i is 0 - so skip 1
106            for &id2 in ids.iter().skip(i + 1) {
107                assert_ne!(id1, id2, "WorldIds should not repeat");
108            }
109        }
110    }
111
112    #[test]
113    fn world_id_system_param() {
114        fn test_system(world_id: WorldId) -> WorldId {
115            world_id
116        }
117
118        let mut world = World::default();
119        let system_id = world.register_system(test_system);
120        let world_id = world.run_system(system_id).unwrap();
121        assert_eq!(world.id(), world_id);
122    }
123
124    #[test]
125    fn world_id_exclusive_system_param() {
126        fn test_system(_world: &mut World, world_id: WorldId) -> WorldId {
127            world_id
128        }
129
130        let mut world = World::default();
131        let system_id = world.register_system(test_system);
132        let world_id = world.run_system(system_id).unwrap();
133        assert_eq!(world.id(), world_id);
134    }
135
136    // We cannot use this test as-is, as it causes other tests to panic due to using the same atomic variable.
137    // #[test]
138    // #[should_panic]
139    // fn panic_on_overflow() {
140    //     MAX_WORLD_ID.store(usize::MAX - 50, Ordering::Relaxed);
141    //     std::iter::repeat_with(WorldId::new)
142    //         .take(500)
143    //         .for_each(|_| ());
144    // }
145}
bevy_ecs/world/identifier.rs

bevy_ecs/world/
identifier.rs
