polars_utils/
cell.rs

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1//! Copy pasted from std::cell::SyncUnsafeCell
2//! can be removed once the feature stabilizes.
3use std::cell::UnsafeCell;
4
5/// [`UnsafeCell`], but [`Sync`].
6///
7/// This is just an [`UnsafeCell`], except it implements [`Sync`]
8/// if `T` implements [`Sync`].
9///
10/// [`UnsafeCell`] doesn't implement [`Sync`], to prevent accidental misuse.
11/// You can use [`SyncUnsafeCell`] instead of [`UnsafeCell`] to allow it to be
12/// shared between threads, if that's intentional.
13/// Providing proper synchronization is still the task of the user,
14/// making this type just as unsafe to use.
15///
16/// See [`UnsafeCell`] for details.
17#[repr(transparent)]
18pub struct SyncUnsafeCell<T: ?Sized> {
19    value: UnsafeCell<T>,
20}
21
22unsafe impl<T: ?Sized + Sync> Sync for SyncUnsafeCell<T> {}
23
24impl<T> SyncUnsafeCell<T> {
25    /// Constructs a new instance of [`SyncUnsafeCell`] which will wrap the specified value.
26    #[inline]
27    pub fn new(value: T) -> Self {
28        Self {
29            value: UnsafeCell::new(value),
30        }
31    }
32
33    /// Unwraps the value.
34    #[inline]
35    pub fn into_inner(self) -> T {
36        self.value.into_inner()
37    }
38}
39
40impl<T: ?Sized> SyncUnsafeCell<T> {
41    /// Gets a mutable pointer to the wrapped value.
42    ///
43    /// This can be cast to a pointer of any kind.
44    /// Ensure that the access is unique (no active references, mutable or not)
45    /// when casting to `&mut T`, and ensure that there are no mutations
46    /// or mutable aliases going on when casting to `&T`
47    #[inline]
48    pub fn get(&self) -> *mut T {
49        self.value.get()
50    }
51
52    /// Returns a mutable reference to the underlying data.
53    ///
54    /// This call borrows the [`SyncUnsafeCell`] mutably (at compile-time) which
55    /// guarantees that we possess the only reference.
56    #[inline]
57    pub fn get_mut(&mut self) -> &mut T {
58        self.value.get_mut()
59    }
60
61    /// Gets a mutable pointer to the wrapped value.
62    ///
63    /// See [`UnsafeCell::get`] for details.
64    #[inline]
65    pub fn raw_get(this: *const Self) -> *mut T {
66        // We can just cast the pointer from `SyncUnsafeCell<T>` to `T` because
67        // of #[repr(transparent)] on both SyncUnsafeCell and UnsafeCell.
68        // See UnsafeCell::raw_get.
69        this as *const T as *mut T
70    }
71}
72
73impl<T: Default> Default for SyncUnsafeCell<T> {
74    /// Creates an `SyncUnsafeCell`, with the `Default` value for T.
75    fn default() -> SyncUnsafeCell<T> {
76        SyncUnsafeCell::new(Default::default())
77    }
78}
79
80impl<T> From<T> for SyncUnsafeCell<T> {
81    /// Creates a new [`SyncUnsafeCell<T>`] containing the given value.
82    fn from(t: T) -> SyncUnsafeCell<T> {
83        SyncUnsafeCell::new(t)
84    }
85}
polars_utils/cell.rs

polars_utils/
cell.rs
