1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
use crate::archetype::ArchetypeComponentId;
use crate::change_detection::{MutUntyped, TicksMut};
use crate::component::{ComponentId, ComponentTicks, Components, Tick, TickCells};
use crate::storage::{blob_vec::BlobVec, SparseSet};
use bevy_ptr::{OwningPtr, Ptr, UnsafeCellDeref};
use std::{cell::UnsafeCell, mem::ManuallyDrop, thread::ThreadId};

/// The type-erased backing storage and metadata for a single resource within a [`World`].
///
/// If `SEND` is false, values of this type will panic if dropped from a different thread.
///
/// [`World`]: crate::world::World
pub struct ResourceData<const SEND: bool> {
    data: ManuallyDrop<BlobVec>,
    added_ticks: UnsafeCell<Tick>,
    changed_ticks: UnsafeCell<Tick>,
    type_name: String,
    id: ArchetypeComponentId,
    origin_thread_id: Option<ThreadId>,
}

impl<const SEND: bool> Drop for ResourceData<SEND> {
    fn drop(&mut self) {
        if self.is_present() {
            // If this thread is already panicking, panicking again will cause
            // the entire process to abort. In this case we choose to avoid
            // dropping or checking this altogether and just leak the column.
            if std::thread::panicking() {
                return;
            }
            self.validate_access();
        }
        // SAFETY: Drop is only called once upon dropping the ResourceData
        // and is inaccessible after this as the parent ResourceData has
        // been dropped. The validate_access call above will check that the
        // data is dropped on the thread it was inserted from.
        unsafe {
            ManuallyDrop::drop(&mut self.data);
        }
    }
}

impl<const SEND: bool> ResourceData<SEND> {
    /// The only row in the underlying `BlobVec`.
    const ROW: usize = 0;

    /// Validates the access to `!Send` resources is only done on the thread they were created from.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if called from a different thread than the one it was inserted from.
    #[inline]
    fn validate_access(&self) {
        if SEND {
            return;
        }
        if self.origin_thread_id != Some(std::thread::current().id()) {
            // Panic in tests, as testing for aborting is nearly impossible
            panic!(
                "Attempted to access or drop non-send resource {} from thread {:?} on a thread {:?}. This is not allowed. Aborting.",
                self.type_name,
                self.origin_thread_id,
                std::thread::current().id()
            );
        }
    }

    /// Returns true if the resource is populated.
    #[inline]
    pub fn is_present(&self) -> bool {
        !self.data.is_empty()
    }

    /// Gets the [`ArchetypeComponentId`] for the resource.
    #[inline]
    pub fn id(&self) -> ArchetypeComponentId {
        self.id
    }

    /// Returns a reference to the resource, if it exists.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not accessed from the
    /// original thread it was inserted from.
    #[inline]
    pub fn get_data(&self) -> Option<Ptr<'_>> {
        self.is_present().then(|| {
            self.validate_access();
            // SAFETY: We've already checked if a value is present, and there should only be one.
            unsafe { self.data.get_unchecked(Self::ROW) }
        })
    }

    /// Returns a reference to the resource's change ticks, if it exists.
    #[inline]
    pub fn get_ticks(&self) -> Option<ComponentTicks> {
        // SAFETY: This is being fetched through a read-only reference to Self, so no other mutable references
        // to the ticks can exist.
        unsafe {
            self.is_present().then(|| ComponentTicks {
                added: self.added_ticks.read(),
                changed: self.changed_ticks.read(),
            })
        }
    }

    /// Returns references to the resource and its change ticks, if it exists.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not accessed from the
    /// original thread it was inserted in.
    #[inline]
    pub(crate) fn get_with_ticks(&self) -> Option<(Ptr<'_>, TickCells<'_>)> {
        self.is_present().then(|| {
            self.validate_access();
            (
                // SAFETY: We've already checked if a value is present, and there should only be one.
                unsafe { self.data.get_unchecked(Self::ROW) },
                TickCells {
                    added: &self.added_ticks,
                    changed: &self.changed_ticks,
                },
            )
        })
    }

    /// Returns a mutable reference to the resource, if it exists.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not accessed from the
    /// original thread it was inserted in.
    pub(crate) fn get_mut(&mut self, last_run: Tick, this_run: Tick) -> Option<MutUntyped<'_>> {
        let (ptr, ticks) = self.get_with_ticks()?;
        Some(MutUntyped {
            // SAFETY: We have exclusive access to the underlying storage.
            value: unsafe { ptr.assert_unique() },
            // SAFETY: We have exclusive access to the underlying storage.
            ticks: unsafe { TicksMut::from_tick_cells(ticks, last_run, this_run) },
        })
    }

    /// Inserts a value into the resource. If a value is already present
    /// it will be replaced.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not replaced from
    /// the original thread it was inserted in.
    ///
    /// # Safety
    /// - `value` must be valid for the underlying type for the resource.
    #[inline]
    pub(crate) unsafe fn insert(&mut self, value: OwningPtr<'_>, change_tick: Tick) {
        if self.is_present() {
            self.validate_access();
            // SAFETY: The caller ensures that the provided value is valid for the underlying type and
            // is properly initialized. We've ensured that a value is already present and previously
            // initialized.
            unsafe {
                self.data.replace_unchecked(Self::ROW, value);
            }
        } else {
            if !SEND {
                self.origin_thread_id = Some(std::thread::current().id());
            }
            self.data.push(value);
            *self.added_ticks.deref_mut() = change_tick;
        }
        *self.changed_ticks.deref_mut() = change_tick;
    }

    /// Inserts a value into the resource with a pre-existing change tick. If a
    /// value is already present it will be replaced.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not replaced from
    /// the original thread it was inserted in.
    ///
    /// # Safety
    /// - `value` must be valid for the underlying type for the resource.
    #[inline]
    pub(crate) unsafe fn insert_with_ticks(
        &mut self,
        value: OwningPtr<'_>,
        change_ticks: ComponentTicks,
    ) {
        if self.is_present() {
            self.validate_access();
            // SAFETY: The caller ensures that the provided value is valid for the underlying type and
            // is properly initialized. We've ensured that a value is already present and previously
            // initialized.
            unsafe {
                self.data.replace_unchecked(Self::ROW, value);
            }
        } else {
            if !SEND {
                self.origin_thread_id = Some(std::thread::current().id());
            }
            self.data.push(value);
        }
        *self.added_ticks.deref_mut() = change_ticks.added;
        *self.changed_ticks.deref_mut() = change_ticks.changed;
    }

    /// Removes a value from the resource, if present.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not removed from the
    /// original thread it was inserted from.
    #[inline]
    #[must_use = "The returned pointer to the removed component should be used or dropped"]
    pub(crate) fn remove(&mut self) -> Option<(OwningPtr<'_>, ComponentTicks)> {
        if !self.is_present() {
            return None;
        }
        if !SEND {
            self.validate_access();
        }
        // SAFETY: We've already validated that the row is present.
        let res = unsafe { self.data.swap_remove_and_forget_unchecked(Self::ROW) };
        // SAFETY: This function is being called through an exclusive mutable reference to Self, which
        // makes it sound to read these ticks.
        unsafe {
            Some((
                res,
                ComponentTicks {
                    added: self.added_ticks.read(),
                    changed: self.changed_ticks.read(),
                },
            ))
        }
    }

    /// Removes a value from the resource, if present, and drops it.
    ///
    /// # Panics
    /// If `SEND` is false, this will panic if a value is present and is not
    /// accessed from the original thread it was inserted in.
    #[inline]
    pub(crate) fn remove_and_drop(&mut self) {
        if self.is_present() {
            self.validate_access();
            self.data.clear();
        }
    }

    pub(crate) fn check_change_ticks(&mut self, change_tick: Tick) {
        self.added_ticks.get_mut().check_tick(change_tick);
        self.changed_ticks.get_mut().check_tick(change_tick);
    }
}

/// The backing store for all [`Resource`]s stored in the [`World`].
///
/// [`Resource`]: crate::system::Resource
/// [`World`]: crate::world::World
#[derive(Default)]
pub struct Resources<const SEND: bool> {
    resources: SparseSet<ComponentId, ResourceData<SEND>>,
}

impl<const SEND: bool> Resources<SEND> {
    /// The total number of resources stored in the [`World`]
    ///
    /// [`World`]: crate::world::World
    #[inline]
    pub fn len(&self) -> usize {
        self.resources.len()
    }

    /// Iterate over all resources that have been initialized, i.e. given a [`ComponentId`]
    pub fn iter(&self) -> impl Iterator<Item = (ComponentId, &ResourceData<SEND>)> {
        self.resources.iter().map(|(id, data)| (*id, data))
    }

    /// Returns true if there are no resources stored in the [`World`],
    /// false otherwise.
    ///
    /// [`World`]: crate::world::World
    #[inline]
    pub fn is_empty(&self) -> bool {
        self.resources.is_empty()
    }

    /// Gets read-only access to a resource, if it exists.
    #[inline]
    pub fn get(&self, component_id: ComponentId) -> Option<&ResourceData<SEND>> {
        self.resources.get(component_id)
    }

    /// Clears all resources.
    #[inline]
    pub fn clear(&mut self) {
        self.resources.clear();
    }

    /// Gets mutable access to a resource, if it exists.
    #[inline]
    pub(crate) fn get_mut(&mut self, component_id: ComponentId) -> Option<&mut ResourceData<SEND>> {
        self.resources.get_mut(component_id)
    }

    /// Fetches or initializes a new resource and returns back its underlying column.
    ///
    /// # Panics
    /// Will panic if `component_id` is not valid for the provided `components`
    /// If `SEND` is true, this will panic if `component_id`'s `ComponentInfo` is not registered as being `Send` + `Sync`.
    pub(crate) fn initialize_with(
        &mut self,
        component_id: ComponentId,
        components: &Components,
        f: impl FnOnce() -> ArchetypeComponentId,
    ) -> &mut ResourceData<SEND> {
        self.resources.get_or_insert_with(component_id, || {
            let component_info = components.get_info(component_id).unwrap();
            if SEND {
                assert!(
                    component_info.is_send_and_sync(),
                    "Send + Sync resource {} initialized as non_send. It may have been inserted via World::insert_non_send_resource by accident. Try using World::insert_resource instead.",
                    component_info.name(),
                );
            }
            // SAFETY: component_info.drop() is valid for the types that will be inserted.
            let data = unsafe {
                BlobVec::new(
                    component_info.layout(),
                    component_info.drop(),
                    1
                )
            };
            ResourceData {
                data: ManuallyDrop::new(data),
                added_ticks: UnsafeCell::new(Tick::new(0)),
                changed_ticks: UnsafeCell::new(Tick::new(0)),
                type_name: String::from(component_info.name()),
                id: f(),
                origin_thread_id: None,
            }
        })
    }

    pub(crate) fn check_change_ticks(&mut self, change_tick: Tick) {
        for info in self.resources.values_mut() {
            info.check_change_ticks(change_tick);
        }
    }
}