Vendor things

third-party/vendor/triomphe/src/thin_arc.rs

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+use core::cmp::Ordering;
+use core::ffi::c_void;
+use core::fmt;
+use core::hash::{Hash, Hasher};
+use core::iter::{ExactSizeIterator, Iterator};
+use core::marker::PhantomData;
+use core::mem::ManuallyDrop;
+use core::ops::Deref;
+use core::ptr;
+use core::usize;
+
+use super::{Arc, ArcInner, HeaderSliceWithLength, HeaderWithLength};
+
+/// A "thin" `Arc` containing dynamically sized data
+///
+/// This is functionally equivalent to `Arc<(H, [T])>`
+///
+/// When you create an `Arc` containing a dynamically sized type
+/// like `HeaderSlice<H, [T]>`, the `Arc` is represented on the stack
+/// as a "fat pointer", where the length of the slice is stored
+/// alongside the `Arc`'s pointer. In some situations you may wish to
+/// have a thin pointer instead, perhaps for FFI compatibility
+/// or space efficiency.
+///
+/// Note that we use `[T; 0]` in order to have the right alignment for `T`.
+///
+/// `ThinArc` solves this by storing the length in the allocation itself,
+/// via `HeaderSliceWithLength`.
+#[repr(transparent)]
+pub struct ThinArc<H, T> {
+    ptr: ptr::NonNull<ArcInner<HeaderSliceWithLength<H, [T; 0]>>>,
+    phantom: PhantomData<(H, T)>,
+}
+
+unsafe impl<H: Sync + Send, T: Sync + Send> Send for ThinArc<H, T> {}
+unsafe impl<H: Sync + Send, T: Sync + Send> Sync for ThinArc<H, T> {}
+
+// Synthesize a fat pointer from a thin pointer.
+//
+// See the comment around the analogous operation in from_header_and_iter.
+#[inline]
+fn thin_to_thick<H, T>(
+    thin: *mut ArcInner<HeaderSliceWithLength<H, [T; 0]>>,
+) -> *mut ArcInner<HeaderSliceWithLength<H, [T]>> {
+    let len = unsafe { (*thin).data.header.length };
+    let fake_slice = ptr::slice_from_raw_parts_mut(thin as *mut T, len);
+
+    fake_slice as *mut ArcInner<HeaderSliceWithLength<H, [T]>>
+}
+
+impl<H, T> ThinArc<H, T> {
+    /// Temporarily converts |self| into a bonafide Arc and exposes it to the
+    /// provided callback. The refcount is not modified.
+    #[inline]
+    pub fn with_arc<F, U>(&self, f: F) -> U
+    where
+        F: FnOnce(&Arc<HeaderSliceWithLength<H, [T]>>) -> U,
+    {
+        // Synthesize transient Arc, which never touches the refcount of the ArcInner.
+        let transient = unsafe {
+            ManuallyDrop::new(Arc {
+                p: ptr::NonNull::new_unchecked(thin_to_thick(self.ptr.as_ptr())),
+                phantom: PhantomData,
+            })
+        };
+
+        // Expose the transient Arc to the callback, which may clone it if it wants
+        // and forward the result to the user
+        f(&transient)
+    }
+
+    /// Creates a `ThinArc` for a HeaderSlice using the given header struct and
+    /// iterator to generate the slice.
+    pub fn from_header_and_iter<I>(header: H, items: I) -> Self
+    where
+        I: Iterator<Item = T> + ExactSizeIterator,
+    {
+        let header = HeaderWithLength::new(header, items.len());
+        Arc::into_thin(Arc::from_header_and_iter(header, items))
+    }
+
+    /// Creates a `ThinArc` for a HeaderSlice using the given header struct and
+    /// a slice to copy.
+    pub fn from_header_and_slice(header: H, items: &[T]) -> Self
+    where
+        T: Copy,
+    {
+        let header = HeaderWithLength::new(header, items.len());
+        Arc::into_thin(Arc::from_header_and_slice(header, items))
+    }
+
+    /// Returns the address on the heap of the ThinArc itself -- not the T
+    /// within it -- for memory reporting.
+    #[inline]
+    pub fn ptr(&self) -> *const c_void {
+        self.ptr.as_ptr() as *const ArcInner<T> as *const c_void
+    }
+
+    /// Returns the address on the heap of the Arc itself -- not the T within it -- for memory
+    /// reporting.
+    #[inline]
+    pub fn heap_ptr(&self) -> *const c_void {
+        self.ptr()
+    }
+
+    /// # Safety
+    ///
+    /// Constructs an ThinArc from a raw pointer.
+    ///
+    /// The raw pointer must have been previously returned by a call to
+    /// ThinArc::into_raw.
+    ///
+    /// The user of from_raw has to make sure a specific value of T is only dropped once.
+    ///
+    /// This function is unsafe because improper use may lead to memory unsafety,
+    /// even if the returned ThinArc is never accessed.
+    #[inline]
+    pub unsafe fn from_raw(ptr: *const c_void) -> Self {
+        Self {
+            ptr: ptr::NonNull::new_unchecked(ptr as *mut c_void).cast(),
+            phantom: PhantomData,
+        }
+    }
+
+    /// Consume ThinArc and returned the wrapped pointer.
+    #[inline]
+    pub fn into_raw(self) -> *const c_void {
+        let this = ManuallyDrop::new(self);
+        this.ptr.cast().as_ptr()
+    }
+
+    /// Provides a raw pointer to the data.
+    /// The counts are not affected in any way and the ThinArc is not consumed.
+    /// The pointer is valid for as long as there are strong counts in the ThinArc.
+    #[inline]
+    pub fn as_ptr(&self) -> *const c_void {
+        self.ptr()
+    }
+}
+
+impl<H, T> Deref for ThinArc<H, T> {
+    type Target = HeaderSliceWithLength<H, [T]>;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        unsafe { &(*thin_to_thick(self.ptr.as_ptr())).data }
+    }
+}
+
+impl<H, T> Clone for ThinArc<H, T> {
+    #[inline]
+    fn clone(&self) -> Self {
+        ThinArc::with_arc(self, |a| {
+            // Safety: `a` isn't mutable thus the header length remains valid
+            unsafe { Arc::into_thin_unchecked(a.clone()) }
+        })
+    }
+}
+
+impl<H, T> Drop for ThinArc<H, T> {
+    #[inline]
+    fn drop(&mut self) {
+        let _ = Arc::from_thin(ThinArc {
+            ptr: self.ptr,
+            phantom: PhantomData,
+        });
+    }
+}
+
+impl<H, T> Arc<HeaderSliceWithLength<H, [T]>> {
+    /// Converts an `Arc` into a `ThinArc`. This consumes the `Arc`, so the refcount
+    /// is not modified.
+    ///
+    /// # Safety
+    /// Assumes that the header length matches the slice length.
+    #[inline]
+    unsafe fn into_thin_unchecked(a: Self) -> ThinArc<H, T> {
+        let a = ManuallyDrop::new(a);
+        debug_assert_eq!(
+            a.header.length,
+            a.slice.len(),
+            "Length needs to be correct for ThinArc to work"
+        );
+        let fat_ptr: *mut ArcInner<HeaderSliceWithLength<H, [T]>> = a.ptr();
+        let thin_ptr = fat_ptr as *mut [usize] as *mut usize;
+        ThinArc {
+            ptr: unsafe {
+                ptr::NonNull::new_unchecked(
+                    thin_ptr as *mut ArcInner<HeaderSliceWithLength<H, [T; 0]>>,
+                )
+            },
+            phantom: PhantomData,
+        }
+    }
+
+    /// Converts an `Arc` into a `ThinArc`. This consumes the `Arc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn into_thin(a: Self) -> ThinArc<H, T> {
+        assert_eq!(
+            a.header.length,
+            a.slice.len(),
+            "Length needs to be correct for ThinArc to work"
+        );
+        unsafe { Self::into_thin_unchecked(a) }
+    }
+
+    /// Converts a `ThinArc` into an `Arc`. This consumes the `ThinArc`, so the refcount
+    /// is not modified.
+    #[inline]
+    pub fn from_thin(a: ThinArc<H, T>) -> Self {
+        let a = ManuallyDrop::new(a);
+        let ptr = thin_to_thick(a.ptr.as_ptr());
+        unsafe {
+            Arc {
+                p: ptr::NonNull::new_unchecked(ptr),
+                phantom: PhantomData,
+            }
+        }
+    }
+}
+
+impl<H: PartialEq, T: PartialEq> PartialEq for ThinArc<H, T> {
+    #[inline]
+    fn eq(&self, other: &ThinArc<H, T>) -> bool {
+        ThinArc::with_arc(self, |a| ThinArc::with_arc(other, |b| *a == *b))
+    }
+}
+
+impl<H: Eq, T: Eq> Eq for ThinArc<H, T> {}
+
+impl<H: PartialOrd, T: PartialOrd> PartialOrd for ThinArc<H, T> {
+    #[inline]
+    fn partial_cmp(&self, other: &ThinArc<H, T>) -> Option<Ordering> {
+        ThinArc::with_arc(self, |a| ThinArc::with_arc(other, |b| a.partial_cmp(b)))
+    }
+}
+
+impl<H: Ord, T: Ord> Ord for ThinArc<H, T> {
+    #[inline]
+    fn cmp(&self, other: &ThinArc<H, T>) -> Ordering {
+        ThinArc::with_arc(self, |a| ThinArc::with_arc(other, |b| a.cmp(b)))
+    }
+}
+
+impl<H: Hash, T: Hash> Hash for ThinArc<H, T> {
+    fn hash<HSR: Hasher>(&self, state: &mut HSR) {
+        ThinArc::with_arc(self, |a| a.hash(state))
+    }
+}
+
+impl<H: fmt::Debug, T: fmt::Debug> fmt::Debug for ThinArc<H, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+impl<H, T> fmt::Pointer for ThinArc<H, T> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Pointer::fmt(&self.ptr(), f)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Arc, HeaderWithLength, ThinArc};
+    use alloc::vec;
+    use core::clone::Clone;
+    use core::ops::Drop;
+    use core::sync::atomic;
+    use core::sync::atomic::Ordering::{Acquire, SeqCst};
+
+    #[derive(PartialEq)]
+    struct Canary(*mut atomic::AtomicUsize);
+
+    impl Drop for Canary {
+        fn drop(&mut self) {
+            unsafe {
+                (*self.0).fetch_add(1, SeqCst);
+            }
+        }
+    }
+
+    #[test]
+    fn empty_thin() {
+        let header = HeaderWithLength::new(100u32, 0);
+        let x = Arc::from_header_and_iter(header, core::iter::empty::<i32>());
+        let y = Arc::into_thin(x.clone());
+        assert_eq!(y.header.header, 100);
+        assert!(y.slice.is_empty());
+        assert_eq!(x.header.header, 100);
+        assert!(x.slice.is_empty());
+    }
+
+    #[test]
+    fn thin_assert_padding() {
+        #[derive(Clone, Default)]
+        #[repr(C)]
+        struct Padded {
+            i: u16,
+        }
+
+        // The header will have more alignment than `Padded`
+        let header = HeaderWithLength::new(0i32, 2);
+        let items = vec![Padded { i: 0xdead }, Padded { i: 0xbeef }];
+        let a = ThinArc::from_header_and_iter(header, items.into_iter());
+        assert_eq!(a.slice.len(), 2);
+        assert_eq!(a.slice[0].i, 0xdead);
+        assert_eq!(a.slice[1].i, 0xbeef);
+    }
+
+    #[test]
+    #[allow(clippy::redundant_clone, clippy::eq_op)]
+    fn slices_and_thin() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            let x = Arc::into_thin(Arc::from_header_and_slice(header, &v));
+            let y = ThinArc::with_arc(&x, |q| q.clone());
+            let _ = y.clone();
+            let _ = x == x;
+            Arc::from_thin(x.clone());
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+
+    #[test]
+    #[allow(clippy::redundant_clone, clippy::eq_op)]
+    fn iter_and_thin() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            let x = Arc::into_thin(Arc::from_header_and_iter(header, v.into_iter()));
+            let y = ThinArc::with_arc(&x, |q| q.clone());
+            let _ = y.clone();
+            let _ = x == x;
+            Arc::from_thin(x.clone());
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+
+    #[test]
+    fn into_raw_and_from_raw() {
+        let mut canary = atomic::AtomicUsize::new(0);
+        let c = Canary(&mut canary as *mut atomic::AtomicUsize);
+        let v = vec![5, 6];
+        let header = HeaderWithLength::new(c, v.len());
+        {
+            type ThinArcCanary = ThinArc<Canary, u32>;
+            let x: ThinArcCanary = Arc::into_thin(Arc::from_header_and_iter(header, v.into_iter()));
+            let ptr = x.as_ptr();
+
+            assert_eq!(x.into_raw(), ptr);
+
+            let _x = unsafe { ThinArcCanary::from_raw(ptr) };
+        }
+        assert_eq!(canary.load(Acquire), 1);
+    }
+
+    #[test]
+    fn thin_eq_and_cmp() {
+        [
+            [("*", &b"AB"[..]), ("*", &b"ab"[..])],
+            [("*", &b"AB"[..]), ("*", &b"a"[..])],
+            [("*", &b"A"[..]), ("*", &b"ab"[..])],
+            [("A", &b"*"[..]), ("a", &b"*"[..])],
+            [("a", &b"*"[..]), ("A", &b"*"[..])],
+            [("AB", &b"*"[..]), ("a", &b"*"[..])],
+            [("A", &b"*"[..]), ("ab", &b"*"[..])],
+        ]
+        .iter()
+        .for_each(|[lt @ (lh, ls), rt @ (rh, rs)]| {
+            let l = ThinArc::from_header_and_slice(lh, ls);
+            let r = ThinArc::from_header_and_slice(rh, rs);
+
+            assert_eq!(l, l);
+            assert_eq!(r, r);
+
+            assert_ne!(l, r);
+            assert_ne!(r, l);
+
+            assert_eq!(l <= l, lt <= lt, "{lt:?} <= {lt:?}");
+            assert_eq!(l >= l, lt >= lt, "{lt:?} >= {lt:?}");
+
+            assert_eq!(l < l, lt < lt, "{lt:?} < {lt:?}");
+            assert_eq!(l > l, lt > lt, "{lt:?} > {lt:?}");
+
+            assert_eq!(r <= r, rt <= rt, "{rt:?} <= {rt:?}");
+            assert_eq!(r >= r, rt >= rt, "{rt:?} >= {rt:?}");
+
+            assert_eq!(r < r, rt < rt, "{rt:?} < {rt:?}");
+            assert_eq!(r > r, rt > rt, "{rt:?} > {rt:?}");
+
+            assert_eq!(l < r, lt < rt, "{lt:?} < {rt:?}");
+            assert_eq!(r > l, rt > lt, "{rt:?} > {lt:?}");
+        })
+    }
+
+    #[test]
+    fn thin_eq_and_partial_cmp() {
+        [
+            [(0.0, &[0.0, 0.0][..]), (1.0, &[0.0, 0.0][..])],
+            [(1.0, &[0.0, 0.0][..]), (0.0, &[0.0, 0.0][..])],
+            [(0.0, &[0.0][..]), (0.0, &[0.0, 0.0][..])],
+            [(0.0, &[0.0, 0.0][..]), (0.0, &[0.0][..])],
+            [(0.0, &[1.0, 2.0][..]), (0.0, &[10.0, 20.0][..])],
+        ]
+        .iter()
+        .for_each(|[lt @ (lh, ls), rt @ (rh, rs)]| {
+            let l = ThinArc::from_header_and_slice(lh, ls);
+            let r = ThinArc::from_header_and_slice(rh, rs);
+
+            assert_eq!(l, l);
+            assert_eq!(r, r);
+
+            assert_ne!(l, r);
+            assert_ne!(r, l);
+
+            assert_eq!(l <= l, lt <= lt, "{lt:?} <= {lt:?}");
+            assert_eq!(l >= l, lt >= lt, "{lt:?} >= {lt:?}");
+
+            assert_eq!(l < l, lt < lt, "{lt:?} < {lt:?}");
+            assert_eq!(l > l, lt > lt, "{lt:?} > {lt:?}");
+
+            assert_eq!(r <= r, rt <= rt, "{rt:?} <= {rt:?}");
+            assert_eq!(r >= r, rt >= rt, "{rt:?} >= {rt:?}");
+
+            assert_eq!(r < r, rt < rt, "{rt:?} < {rt:?}");
+            assert_eq!(r > r, rt > rt, "{rt:?} > {rt:?}");
+
+            assert_eq!(l < r, lt < rt, "{lt:?} < {rt:?}");
+            assert_eq!(r > l, rt > lt, "{rt:?} > {lt:?}");
+        })
+    }
+
+    #[allow(dead_code)]
+    const fn is_partial_ord<T: ?Sized + PartialOrd>() {}
+
+    #[allow(dead_code)]
+    const fn is_ord<T: ?Sized + Ord>() {}
+
+    // compile-time check that PartialOrd/Ord is correctly derived
+    const _: () = is_partial_ord::<ThinArc<f64, f64>>();
+    const _: () = is_partial_ord::<ThinArc<f64, u64>>();
+    const _: () = is_partial_ord::<ThinArc<u64, f64>>();
+    const _: () = is_ord::<ThinArc<u64, u64>>();
+}