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// Copyright © SixtyFPS GmbH <info@slint.dev>
// SPDX-License-Identifier: MIT OR Apache-2.0
// cSpell: ignore pointee repr
//! implementation of vtable::Vrc
use super::*;
use portable_atomic::{AtomicU32, Ordering};
/// This trait is implemented by the [`#[vtable]`](macro@vtable) macro.
///
/// It is implemented if the macro has a "drop_in_place" function.
///
/// # Safety
///
/// The implementation of drop_in_place and dealloc must be correct
pub unsafe trait VTableMetaDropInPlace: VTableMeta {
/// # Safety
/// The target ptr argument needs to be pointing to a an instance of the VTable
/// after the call to this function, the memory is still there but no longer contains
/// a valid object.
unsafe fn drop_in_place(vtable: &Self::VTable, ptr: *mut u8) -> vrc::Layout;
/// # Safety
/// The target ptr must have been allocated by the same allocator as the
/// one which the vtable will delegate to.
unsafe fn dealloc(vtable: &Self::VTable, ptr: *mut u8, layout: vrc::Layout);
}
/// This is a marker type to be used in [`VRc`] and [`VWeak`] to mean that the
/// actual type is not known.
pub struct Dyn(());
/// Similar to [`core::alloc::Layout`], but `repr(C)`
#[repr(C)]
#[derive(Clone, Copy)]
pub struct Layout {
/// The size in bytes
pub size: usize,
/// The minimum alignment in bytes
pub align: usize,
}
impl From<core::alloc::Layout> for Layout {
fn from(layout: core::alloc::Layout) -> Self {
Self { size: layout.size(), align: layout.align() }
}
}
impl core::convert::TryFrom<Layout> for core::alloc::Layout {
type Error = core::alloc::LayoutError;
fn try_from(value: Layout) -> Result<Self, Self::Error> {
Self::from_size_align(value.size, value.align)
}
}
#[repr(C)]
struct VRcInner<'vt, VTable: VTableMeta, X> {
vtable: &'vt VTable::VTable,
/// The amount of VRc pointing to this object. When it reaches 0, the object will be dropped
strong_ref: AtomicU32,
/// The amount of VWeak +1. When it reaches 0, the memory will be deallocated.
/// The +1 is there such as all the VRc together hold a weak reference to the memory
weak_ref: AtomicU32,
/// offset to the data from the beginning of VRcInner. This is needed to cast a VRcInner<VT, X>
/// to VRcInner<VT, u8> as "dyn VRc" and then still be able to get the correct data pointer,
/// since the alignment of X may not be the same as u8.
data_offset: u16,
/// Actual data, or an instance of `Self::Layout` iff `strong_ref == 0`.
/// Can be seen as `union {data: X, layout: Layout}` (but that's not stable)
data: X,
}
impl<'vt, VTable: VTableMeta, X> VRcInner<'vt, VTable, X> {
unsafe fn data_ptr(s: *const Self) -> *const X {
(s as *const u8).add(*core::ptr::addr_of!((*s).data_offset) as usize) as *const X
}
fn as_ref(&self) -> &X {
let ptr = self as *const Self as *const u8;
unsafe { &*(ptr.add(self.data_offset as usize) as *const X) }
}
}
/// A reference counted pointer to an object matching the virtual table `T`
///
/// Similar to [`alloc::rc::Rc`] where the `VTable` type parameter is a VTable struct
/// annotated with [`#[vtable]`](macro@vtable), and the `X` type parameter is the actual instance.
/// When `X` is the [`Dyn`] type marker, this means that the X is not known and the only
/// thing that can be done is to get a [`VRef<VTable>`] through the [`Self::borrow()`] function.
///
/// Other differences with the [`alloc::rc::Rc`] types are:
/// - It does not allow to access mutable reference. (No `get_mut` or `make_mut`), meaning it is
/// safe to get a Pin reference with `borrow_pin`.
/// - It is safe to pass it across ffi boundaries.
#[repr(transparent)]
pub struct VRc<VTable: VTableMetaDropInPlace + 'static, X = Dyn> {
inner: NonNull<VRcInner<'static, VTable, X>>,
}
impl<VTable: VTableMetaDropInPlace + 'static, X> Drop for VRc<VTable, X> {
fn drop(&mut self) {
unsafe {
let inner = self.inner.as_ptr();
if (*inner).strong_ref.fetch_sub(1, Ordering::SeqCst) == 1 {
let data =
(inner as *mut u8).add(*core::ptr::addr_of!((*inner).data_offset) as usize);
let vtable = core::ptr::addr_of!((*inner).vtable);
let mut layout = VTable::drop_in_place(*vtable, data);
layout = core::alloc::Layout::new::<VRcInner<VTable, ()>>()
.extend(layout.try_into().unwrap())
.unwrap()
.0
.pad_to_align()
.into();
if (*core::ptr::addr_of!((*inner).weak_ref)).load(Ordering::SeqCst) > 1 {
// at this point we are sure that no other thread can access the data
// since we still hold a weak reference, so the other weak references
// in other thread won't start destroying the object.
*(VRcInner::data_ptr(self.inner.cast::<VRcInner<VTable, Layout>>().as_ptr())
as *mut Layout) = layout;
}
if (*core::ptr::addr_of!((*inner).weak_ref)).fetch_sub(1, Ordering::SeqCst) == 1 {
VTable::dealloc(*vtable, self.inner.cast().as_ptr(), layout);
}
}
}
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X> core::fmt::Debug for VRc<VTable, X> {
fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
f.debug_struct("VRc").field("inner", &self.inner).finish()
}
}
impl<VTable: VTableMetaDropInPlace, X: HasStaticVTable<VTable>> VRc<VTable, X> {
/// Create a new VRc from an instance of a type that can be associated with a VTable.
///
/// Will move the instance on the heap.
///
/// (the `HasStaticVTable` is implemented by the `“MyTrait”VTable_static!` macro generated by
/// the #[vtable] macro)
pub fn new(data: X) -> Self {
let layout = core::alloc::Layout::new::<VRcInner<VTable, X>>().pad_to_align();
// We must ensure the size is enough to hold a Layout when strong_count becomes 0
let layout_with_layout = core::alloc::Layout::new::<VRcInner<VTable, Layout>>();
let layout = core::alloc::Layout::from_size_align(
layout.size().max(layout_with_layout.size()),
layout.align().max(layout_with_layout.align()),
)
.unwrap();
let mem = unsafe { alloc::alloc::alloc(layout) as *mut VRcInner<VTable, X> };
let inner = NonNull::new(mem).unwrap();
assert!(!mem.is_null());
unsafe {
mem.write(VRcInner {
vtable: X::static_vtable(),
strong_ref: AtomicU32::new(1),
weak_ref: AtomicU32::new(1), // All the VRc together hold a weak_ref to the memory
data_offset: 0,
data,
});
(*mem).data_offset =
(&(*mem).data as *const _ as usize - mem as *const _ as usize) as u16;
VRc { inner }
}
}
/// Convert a VRc of a real instance to a VRc of a Dyn instance
pub fn into_dyn(this: Self) -> VRc<VTable, Dyn>
where
Self: 'static,
{
// Safety: they have the exact same representation: just a pointer to the same structure.
// no Drop will be called here, so no need to increment any ref count
unsafe { core::mem::transmute(this) }
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X: HasStaticVTable<VTable> + 'static> VRc<VTable, X> {
/// This function allows safely holding a reference to a field inside the VRc. In order to accomplish
/// that, you need to provide a mapping function `map_fn` in which you need to provide and return a
/// pinned reference to the object you would like to map. The returned `VRcMapped` allows obtaining
/// that pinned reference again using [`VRcMapped::as_pin_ref`].
pub fn map<MappedType: ?Sized>(
this: Self,
map_fn: impl for<'r> FnOnce(Pin<&'r X>) -> Pin<&'r MappedType>,
) -> VRcMapped<VTable, MappedType> {
VRcMapped {
parent_strong: Self::into_dyn(this.clone()),
object: map_fn(this.as_pin_ref()).get_ref(),
}
}
}
impl<VTable: VTableMetaDropInPlace + 'static> VRc<VTable, Dyn> {
/// This function allows safely holding a reference to a field inside the VRc. In order to accomplish
/// that, you need to provide a mapping function `map_fn` in which you need to provide and return a
/// pinned reference to the object you would like to map. The returned `VRcMapped` allows obtaining
/// that pinned reference again using [`VRcMapped::as_pin_ref`].
/// This works similar to [`VRc::map`] except that it works on a type-erased VRc.
pub fn map_dyn<MappedType: ?Sized>(
this: Self,
map_fn: impl for<'r> FnOnce(Pin<VRef<'r, VTable>>) -> Pin<&'r MappedType>,
) -> VRcMapped<VTable, MappedType> {
VRcMapped { parent_strong: this.clone(), object: map_fn(Self::borrow_pin(&this)).get_ref() }
}
}
impl<VTable: VTableMetaDropInPlace, X> VRc<VTable, X> {
/// Create a Pinned reference to the inner.
///
/// This is safe because we don't allow mutable reference to the inner
pub fn as_pin_ref(&self) -> Pin<&X> {
unsafe { Pin::new_unchecked(self) }
}
/// Gets a VRef pointing to this instance
pub fn borrow(this: &Self) -> VRef<'_, VTable> {
unsafe {
let inner = this.inner.cast::<VRcInner<VTable, u8>>();
VRef::from_raw(
NonNull::from(*::core::ptr::addr_of!((*inner.as_ptr()).vtable)),
NonNull::new_unchecked(VRcInner::data_ptr(inner.as_ptr()) as *mut u8),
)
}
}
/// Gets a `Pin<VRef>` pointing to this instance
///
/// This is safe because there is no way to access a mutable reference to the pointee.
/// (There is no `get_mut` or `make_mut`),
pub fn borrow_pin(this: &Self) -> Pin<VRef<VTable>> {
unsafe { Pin::new_unchecked(Self::borrow(this)) }
}
/// Construct a [`VWeak`] pointing to this instance.
pub fn downgrade(this: &Self) -> VWeak<VTable, X> {
let inner = unsafe { this.inner.as_ref() };
inner.weak_ref.fetch_add(1, Ordering::SeqCst);
VWeak { inner: Some(this.inner) }
}
/// Gets the number of strong (VRc) pointers to this allocation.
pub fn strong_count(this: &Self) -> usize {
unsafe { this.inner.as_ref().strong_ref.load(Ordering::SeqCst) as usize }
}
/// Returns true if the two VRc's point to the same allocation
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this.inner == other.inner
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X> Clone for VRc<VTable, X> {
fn clone(&self) -> Self {
let inner = unsafe { self.inner.as_ref() };
inner.strong_ref.fetch_add(1, Ordering::SeqCst);
Self { inner: self.inner }
}
}
impl<VTable: VTableMetaDropInPlace, X /*+ HasStaticVTable<VTable>*/> Deref for VRc<VTable, X> {
type Target = X;
fn deref(&self) -> &Self::Target {
let inner = unsafe { self.inner.as_ref() };
inner.as_ref()
}
}
// Safety: we use atomic reference count for the internal things
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X: Send + Sync> Send for VRc<VTable, X> {}
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X: Send + Sync> Sync for VRc<VTable, X> {}
/// Weak pointer for the [`VRc`] where `VTable` is a VTable struct, and
/// `X` is the type of the instance, or [`Dyn`] if it is not known
///
/// Similar to [`alloc::rc::Weak`].
///
/// Can be constructed with [`VRc::downgrade`] and use [`VWeak::upgrade`]
/// to re-create the original VRc.
#[repr(transparent)]
pub struct VWeak<VTable: VTableMetaDropInPlace + 'static, X = Dyn> {
inner: Option<NonNull<VRcInner<'static, VTable, X>>>,
}
impl<VTable: VTableMetaDropInPlace + 'static, X> Default for VWeak<VTable, X> {
fn default() -> Self {
Self { inner: None }
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X> Clone for VWeak<VTable, X> {
fn clone(&self) -> Self {
if let Some(inner) = self.inner {
let inner = unsafe { inner.as_ref() };
inner.weak_ref.fetch_add(1, Ordering::SeqCst);
}
VWeak { inner: self.inner }
}
}
impl<T: VTableMetaDropInPlace + 'static, X> Drop for VWeak<T, X> {
fn drop(&mut self) {
if let Some(i) = self.inner {
unsafe {
if (*core::ptr::addr_of!((*i.as_ptr()).weak_ref)).fetch_sub(1, Ordering::SeqCst)
== 1
{
// Safety: while allocating, we made sure that the size was big enough to
// hold a VRcInner<T, Layout>.
let vtable = &*core::ptr::addr_of!((*i.as_ptr()).vtable);
let layout = *(VRcInner::data_ptr(i.cast::<VRcInner<T, Layout>>().as_ptr()));
T::dealloc(vtable, i.cast().as_ptr(), layout);
}
}
}
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X> VWeak<VTable, X> {
/// Returns a new `VRc` if some other instance still holds a strong reference to this item.
/// Otherwise, returns None.
pub fn upgrade(&self) -> Option<VRc<VTable, X>> {
if let Some(i) = self.inner {
let inner = unsafe { i.as_ref() };
if inner.strong_ref.load(Ordering::SeqCst) == 0 {
None
} else {
inner.strong_ref.fetch_add(1, Ordering::SeqCst);
Some(VRc { inner: i })
}
} else {
None
}
}
/// Returns true if the two VWeak instances point to the same allocation
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
this.inner == other.inner
}
}
impl<VTable: VTableMetaDropInPlace + 'static, X: HasStaticVTable<VTable> + 'static>
VWeak<VTable, X>
{
/// Convert a VRc of a real instance to a VRc of a Dyn instance
pub fn into_dyn(self) -> VWeak<VTable, Dyn> {
// Safety: they have the exact same representation: just a pointer to the same structure.
// no Drop will be called here, so no need to increment any ref count
unsafe { core::mem::transmute(self) }
}
}
/// Safety: The data VRc manages is held by `VRcInner`, which maintains its address when the VRc
/// is moved.
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X> stable_deref_trait::StableDeref
for VRc<VTable, X>
{
}
/// Safety: The data VRc manages is held by `VRcInner`, and a clone of a VRc merely clones the pointer
/// *to* the `VRcInner`.
unsafe impl<VTable: VTableMetaDropInPlace + 'static, X> stable_deref_trait::CloneStableDeref
for VRc<VTable, X>
{
}
/// VRcMapped allows bundling a VRc of a type along with a reference to an object that's
/// reachable through the data the VRc owns and that satisfies the requirements of a Pin.
/// VRCMapped is constructed using [`VRc::map`] and, like VRc, has a weak counterpart, [`VWeakMapped`].
pub struct VRcMapped<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> {
parent_strong: VRc<VTable, Dyn>,
object: *const MappedType,
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> Clone
for VRcMapped<VTable, MappedType>
{
fn clone(&self) -> Self {
Self { parent_strong: self.parent_strong.clone(), object: self.object }
}
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> VRcMapped<VTable, MappedType> {
/// Returns a new [`VWeakMapped`] that points to this instance and can be upgraded back to
/// a [`Self`] as long as a `VRc`/`VMapped` exists.
pub fn downgrade(this: &Self) -> VWeakMapped<VTable, MappedType> {
VWeakMapped { parent_weak: VRc::downgrade(&this.parent_strong), object: this.object }
}
/// Create a Pinned reference to the mapped type.
///
/// This is safe because the map function returns a pinned reference.
pub fn as_pin_ref(&self) -> Pin<&MappedType> {
unsafe { Pin::new_unchecked(self) }
}
/// This function allows safely holding a reference to a field inside the `VRcMapped`. In order to accomplish
/// that, you need to provide a mapping function `map_fn` in which you need to provide and return a
/// pinned reference to the object you would like to map. The returned `VRcMapped` allows obtaining
/// that pinned reference again using [`VRcMapped::as_pin_ref`].
///
/// See also [`VRc::map`]
pub fn map<ReMappedType: ?Sized>(
this: Self,
map_fn: impl for<'r> FnOnce(Pin<&'r MappedType>) -> Pin<&'r ReMappedType>,
) -> VRcMapped<VTable, ReMappedType> {
VRcMapped {
parent_strong: this.parent_strong.clone(),
object: map_fn(this.as_pin_ref()).get_ref(),
}
}
/// Returns a strong reference to the object that the mapping originates
/// from.
pub fn origin(this: &Self) -> VRc<VTable> {
this.parent_strong.clone()
}
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> Deref
for VRcMapped<VTable, MappedType>
{
type Target = MappedType;
fn deref(&self) -> &Self::Target {
// Safety: self.object was mapped from self.parent_strong, which the VRc
// keeps alive *and* pinned.
unsafe { &*self.object }
}
}
/// VWeakMapped allows bundling a VWeak with a reference to an object that's reachable
/// from the object a successfully upgraded VWeak points to. VWeakMapped's API consists
/// only of the ability to create clones and to attempt upgrading back to a [`VRcMapped`].
pub struct VWeakMapped<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> {
parent_weak: VWeak<VTable, Dyn>,
object: *const MappedType,
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> VWeakMapped<VTable, MappedType> {
/// Returns a new `VRcMapped` if some other instance still holds a strong reference to the owned
/// object. Otherwise, returns None.
pub fn upgrade(&self) -> Option<VRcMapped<VTable, MappedType>> {
self.parent_weak
.upgrade()
.map(|parent| VRcMapped { parent_strong: parent, object: self.object })
}
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType: ?Sized> Clone
for VWeakMapped<VTable, MappedType>
{
fn clone(&self) -> Self {
Self { parent_weak: self.parent_weak.clone(), object: self.object }
}
}
impl<VTable: VTableMetaDropInPlace + 'static, MappedType> Default
for VWeakMapped<VTable, MappedType>
{
fn default() -> Self {
Self { parent_weak: VWeak::default(), object: core::ptr::null() }
}
}