wgpu_hal/noop/
buffer.rs

1use alloc::{sync::Arc, vec::Vec};
2use core::{cell::UnsafeCell, ops::Range, ptr};
3
4#[derive(Clone, Debug)]
5pub struct Buffer {
6    /// This data is potentially accessed mutably in arbitrary non-overlapping slices,
7    /// so we must store it in `UnsafeCell` to avoid making any too-strong no-aliasing claims.
8    storage: Arc<UnsafeCell<[u8]>>,
9
10    /// Size of the allocation.
11    ///
12    /// This is redundant with `storage.get().len()`, but that method is not
13    /// available until our MSRV is 1.79 or greater.
14    size: usize,
15}
16
17/// SAFETY:
18/// This shared mutable data will not be accessed in a way which causes data races;
19/// the obligation to do so is on the caller of the HAL API.
20/// For safe code, `wgpu-core` validation manages appropriate access.
21unsafe impl Send for Buffer {}
22unsafe impl Sync for Buffer {}
23
24impl Buffer {
25    pub(super) fn new(desc: &crate::BufferDescriptor) -> Result<Self, crate::DeviceError> {
26        let &crate::BufferDescriptor {
27            label: _,
28            size,
29            usage: _,
30            memory_flags: _,
31        } = desc;
32
33        let size = usize::try_from(size).map_err(|_| crate::DeviceError::OutOfMemory)?;
34
35        let mut vector: Vec<u8> = Vec::new();
36        vector
37            .try_reserve_exact(size)
38            .map_err(|_| crate::DeviceError::OutOfMemory)?;
39        vector.resize(size, 0);
40        let storage: Arc<[u8]> = Arc::from(vector);
41        debug_assert_eq!(storage.len(), size);
42
43        // SAFETY: `UnsafeCell<[u8]>` and `[u8]` have the same layout.
44        // This is just adding a wrapper type without changing any layout,
45        // because there is not currently a safe language/`std` way to accomplish this.
46        let storage: Arc<UnsafeCell<[u8]>> =
47            unsafe { Arc::from_raw(Arc::into_raw(storage) as *mut UnsafeCell<[u8]>) };
48
49        Ok(Buffer { storage, size })
50    }
51
52    /// Returns a pointer to the memory owned by this buffer within the given `range`.
53    ///
54    /// This may be used to create any number of simultaneous pointers;
55    /// aliasing is only a concern when actually reading, writing, or converting the pointer
56    /// to a reference.
57    pub(super) fn get_slice_ptr(&self, range: crate::MemoryRange) -> *mut [u8] {
58        let base_ptr = self.storage.get();
59        let range = range_to_usize(range, self.size);
60
61        // We must obtain a slice pointer without ever creating a slice reference
62        // that could alias with another slice.
63        ptr::slice_from_raw_parts_mut(
64            // SAFETY: `range_to_usize` bounds checks this addition.
65            unsafe { base_ptr.cast::<u8>().add(range.start) },
66            range.len(),
67        )
68    }
69}
70
71/// Convert a [`crate::MemoryRange`] to `Range<usize>` and bounds check it.
72fn range_to_usize(range: crate::MemoryRange, upper_bound: usize) -> Range<usize> {
73    // Note: these assertions should be impossible to trigger from safe code.
74    // We're doing them anyway since this entire backend is for testing
75    // (except for when it is an unused placeholder)
76    let start = usize::try_from(range.start).expect("range too large");
77    let end = usize::try_from(range.end).expect("range too large");
78    assert!(start <= end && end <= upper_bound, "range out of bounds");
79    start..end
80}
wgpu_hal/noop/buffer.rs

wgpu_hal/noop/
buffer.rs
