// SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2024 Google LLC. //! A linked list implementation. // May not be needed in Rust 1.87.0 (pending beta backport).#![allow(clippy::ptr_eq)] use crate::sync::ArcBorrow;use crate::types::Opaque;use core::iter::{DoubleEndedIterator, FusedIterator};use core::marker::PhantomData;use core::ptr;use pin_init::PinInit; mod impl_list_item_mod;pub use self::impl_list_item_mod::{ impl_has_list_links, impl_has_list_links_self_ptr, impl_list_item, HasListLinks, HasSelfPtr,}; mod arc;pub use self::arc::{impl_list_arc_safe, AtomicTracker, ListArc, ListArcSafe, TryNewListArc}; mod arc_field;pub use self::arc_field::{define_list_arc_field_getter, ListArcField}; /// A linked list.////// All elements in this linked list will be [`ListArc`] references to the value. Since a value can/// only have one `ListArc` (for each pair of prev/next pointers), this ensures that the same/// prev/next pointers are not used for several linked lists.////// # Invariants////// * If the list is empty, then `first` is null. Otherwise, `first` points at the `ListLinks`/// field of the first element in the list./// * All prev/next pointers in `ListLinks` fields of items in the list are valid and form a cycle./// * For every item in the list, the list owns the associated [`ListArc`] reference and has/// exclusive access to the `ListLinks` field.pub struct List<T: ?Sized + ListItem<ID>, const ID: u64 = 0> { first: *mut ListLinksFields, _ty: PhantomData<ListArc<T, ID>>,} // SAFETY: This is a container of `ListArc<T, ID>`, and access to the container allows the same// type of access to the `ListArc<T, ID>` elements.unsafe impl<T, const ID: u64> Send for List<T, ID>where ListArc<T, ID>: Send, T: ?Sized + ListItem<ID>,{}// SAFETY: This is a container of `ListArc<T, ID>`, and access to the container allows the same// type of access to the `ListArc<T, ID>` elements.unsafe impl<T, const ID: u64> Sync for List<T, ID>where ListArc<T, ID>: Sync, T: ?Sized + ListItem<ID>,{} /// Implemented by types where a [`ListArc<Self>`] can be inserted into a [`List`].////// # Safety////// Implementers must ensure that they provide the guarantees documented on methods provided by/// this trait.////// [`ListArc<Self>`]: ListArcpub unsafe trait ListItem<const ID: u64 = 0>: ListArcSafe<ID> { /// Views the [`ListLinks`] for this value. /// /// # Guarantees /// /// If there is a previous call to `prepare_to_insert` and there is no call to `post_remove` /// since the most recent such call, then this returns the same pointer as the one returned by /// the most recent call to `prepare_to_insert`. /// /// Otherwise, the returned pointer points at a read-only [`ListLinks`] with two null pointers. /// /// # Safety /// /// The provided pointer must point at a valid value. (It need not be in an `Arc`.) unsafe fn view_links(me: *const Self) -> *mut ListLinks<ID>; /// View the full value given its [`ListLinks`] field. /// /// Can only be used when the value is in a list. /// /// # Guarantees /// /// * Returns the same pointer as the one passed to the most recent call to `prepare_to_insert`. /// * The returned pointer is valid until the next call to `post_remove`. /// /// # Safety /// /// * The provided pointer must originate from the most recent call to `prepare_to_insert`, or /// from a call to `view_links` that happened after the most recent call to /// `prepare_to_insert`. /// * Since the most recent call to `prepare_to_insert`, the `post_remove` method must not have /// been called. unsafe fn view_value(me: *mut ListLinks<ID>) -> *const Self; /// This is called when an item is inserted into a [`List`]. /// /// # Guarantees /// /// The caller is granted exclusive access to the returned [`ListLinks`] until `post_remove` is /// called. /// /// # Safety /// /// * The provided pointer must point at a valid value in an [`Arc`]. /// * Calls to `prepare_to_insert` and `post_remove` on the same value must alternate. /// * The caller must own the [`ListArc`] for this value. /// * The caller must not give up ownership of the [`ListArc`] unless `post_remove` has been /// called after this call to `prepare_to_insert`. /// /// [`Arc`]: crate::sync::Arc unsafe fn prepare_to_insert(me: *const Self) -> *mut ListLinks<ID>; /// This undoes a previous call to `prepare_to_insert`. /// /// # Guarantees /// /// The returned pointer is the pointer that was originally passed to `prepare_to_insert`. /// /// # Safety /// /// The provided pointer must be the pointer returned by the most recent call to /// `prepare_to_insert`. unsafe fn post_remove(me: *mut ListLinks<ID>) -> *const Self;} #[repr(C)]#[derive(Copy, Clone)]struct ListLinksFields { next: *mut ListLinksFields, prev: *mut ListLinksFields,} /// The prev/next pointers for an item in a linked list.////// # Invariants////// The fields are null if and only if this item is not in a list.#[repr(transparent)]pub struct ListLinks<const ID: u64 = 0> { // This type is `!Unpin` for aliasing reasons as the pointers are part of an intrusive linked // list. inner: Opaque<ListLinksFields>,} // SAFETY: The only way to access/modify the pointers inside of `ListLinks<ID>` is via holding the// associated `ListArc<T, ID>`. Since that type correctly implements `Send`, it is impossible to// move this an instance of this type to a different thread if the pointees are `!Send`.unsafe impl<const ID: u64> Send for ListLinks<ID> {}// SAFETY: The type is opaque so immutable references to a ListLinks are useless. Therefore, it's// okay to have immutable access to a ListLinks from several threads at once.unsafe impl<const ID: u64> Sync for ListLinks<ID> {} impl<const ID: u64> ListLinks<ID> { /// Creates a new initializer for this type. pub fn new() -> impl PinInit<Self> { // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will // not be constructed in an `Arc` that already has a `ListArc`. ListLinks { inner: Opaque::new(ListLinksFields { prev: ptr::null_mut(), next: ptr::null_mut(), }), } } /// # Safety /// /// `me` must be dereferenceable. #[inline] unsafe fn fields(me: *mut Self) -> *mut ListLinksFields { // SAFETY: The caller promises that the pointer is valid. unsafe { Opaque::raw_get(ptr::addr_of!((*me).inner)) } } /// # Safety /// /// `me` must be dereferenceable. #[inline] unsafe fn from_fields(me: *mut ListLinksFields) -> *mut Self { me.cast() }} /// Similar to [`ListLinks`], but also contains a pointer to the full value.////// This type can be used instead of [`ListLinks`] to support lists with trait objects.#[repr(C)]pub struct ListLinksSelfPtr<T: ?Sized, const ID: u64 = 0> { /// The `ListLinks` field inside this value. /// /// This is public so that it can be used with `impl_has_list_links!`. pub inner: ListLinks<ID>, // UnsafeCell is not enough here because we use `Opaque::uninit` as a dummy value, and // `ptr::null()` doesn't work for `T: ?Sized`. self_ptr: Opaque<*const T>,} // SAFETY: The fields of a ListLinksSelfPtr can be moved across thread boundaries.unsafe impl<T: ?Sized + Send, const ID: u64> Send for ListLinksSelfPtr<T, ID> {}// SAFETY: The type is opaque so immutable references to a ListLinksSelfPtr are useless. Therefore,// it's okay to have immutable access to a ListLinks from several threads at once.//// Note that `inner` being a public field does not prevent this type from being opaque, since// `inner` is a opaque type.unsafe impl<T: ?Sized + Sync, const ID: u64> Sync for ListLinksSelfPtr<T, ID> {} impl<T: ?Sized, const ID: u64> ListLinksSelfPtr<T, ID> { /// The offset from the [`ListLinks`] to the self pointer field. pub const LIST_LINKS_SELF_PTR_OFFSET: usize = core::mem::offset_of!(Self, self_ptr); /// Creates a new initializer for this type. pub fn new() -> impl PinInit<Self> { // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will // not be constructed in an `Arc` that already has a `ListArc`. Self { inner: ListLinks { inner: Opaque::new(ListLinksFields { prev: ptr::null_mut(), next: ptr::null_mut(), }), }, self_ptr: Opaque::uninit(), } }} impl<T: ?Sized + ListItem<ID>, const ID: u64> List<T, ID> { /// Creates a new empty list. pub const fn new() -> Self { Self { first: ptr::null_mut(), _ty: PhantomData, } } /// Returns whether this list is empty. pub fn is_empty(&self) -> bool { self.first.is_null() } /// Inserts `item` before `next` in the cycle. /// /// Returns a pointer to the newly inserted element. Never changes `self.first` unless the list /// is empty. /// /// # Safety /// /// * `next` must be an element in this list or null. /// * if `next` is null, then the list must be empty. unsafe fn insert_inner( &mut self, item: ListArc<T, ID>, next: *mut ListLinksFields, ) -> *mut ListLinksFields { let raw_item = ListArc::into_raw(item); // SAFETY: // * We just got `raw_item` from a `ListArc`, so it's in an `Arc`. // * Since we have ownership of the `ListArc`, `post_remove` must have been called after // the most recent call to `prepare_to_insert`, if any. // * We own the `ListArc`. // * Removing items from this list is always done using `remove_internal_inner`, which // calls `post_remove` before giving up ownership. let list_links = unsafe { T::prepare_to_insert(raw_item) }; // SAFETY: We have not yet called `post_remove`, so `list_links` is still valid. let item = unsafe { ListLinks::fields(list_links) }; // Check if the list is empty. if next.is_null() { // SAFETY: The caller just gave us ownership of these fields. // INVARIANT: A linked list with one item should be cyclic. unsafe { (*item).next = item; (*item).prev = item; } self.first = item; } else { // SAFETY: By the type invariant, this pointer is valid or null. We just checked that // it's not null, so it must be valid. let prev = unsafe { (*next).prev }; // SAFETY: Pointers in a linked list are never dangling, and the caller just gave us // ownership of the fields on `item`. // INVARIANT: This correctly inserts `item` between `prev` and `next`. unsafe { (*item).next = next; (*item).prev = prev; (*prev).next = item; (*next).prev = item; } } item } /// Add the provided item to the back of the list. pub fn push_back(&mut self, item: ListArc<T, ID>) { // SAFETY: // * `self.first` is null or in the list. // * `self.first` is only null if the list is empty. unsafe { self.insert_inner(item, self.first) }; } /// Add the provided item to the front of the list. pub fn push_front(&mut self, item: ListArc<T, ID>) { // SAFETY: // * `self.first` is null or in the list. // * `self.first` is only null if the list is empty. let new_elem = unsafe { self.insert_inner(item, self.first) }; // INVARIANT: `new_elem` is in the list because we just inserted it. self.first = new_elem; } /// Removes the last item from this list. pub fn pop_back(&mut self) -> Option<ListArc<T, ID>> { if self.first.is_null() { return None; } // SAFETY: We just checked that the list is not empty. let last = unsafe { (*self.first).prev }; // SAFETY: The last item of this list is in this list. Some(unsafe { self.remove_internal(last) }) } /// Removes the first item from this list. pub fn pop_front(&mut self) -> Option<ListArc<T, ID>> { if self.first.is_null() { return None; } // SAFETY: The first item of this list is in this list. Some(unsafe { self.remove_internal(self.first) }) } /// Removes the provided item from this list and returns it. /// /// This returns `None` if the item is not in the list. (Note that by the safety requirements, /// this means that the item is not in any list.) /// /// # Safety /// /// `item` must not be in a different linked list (with the same id). pub unsafe fn remove(&mut self, item: &T) -> Option<ListArc<T, ID>> { // SAFETY: TODO. let mut item = unsafe { ListLinks::fields(T::view_links(item)) }; // SAFETY: The user provided a reference, and reference are never dangling. // // As for why this is not a data race, there are two cases: // // * If `item` is not in any list, then these fields are read-only and null. // * If `item` is in this list, then we have exclusive access to these fields since we // have a mutable reference to the list. // // In either case, there's no race. let ListLinksFields { next, prev } = unsafe { *item }; debug_assert_eq!(next.is_null(), prev.is_null()); if !next.is_null() { // This is really a no-op, but this ensures that `item` is a raw pointer that was // obtained without going through a pointer->reference->pointer conversion roundtrip. // This ensures that the list is valid under the more restrictive strict provenance // ruleset. // // SAFETY: We just checked that `next` is not null, and it's not dangling by the // list invariants. unsafe { debug_assert_eq!(item, (*next).prev); item = (*next).prev; } // SAFETY: We just checked that `item` is in a list, so the caller guarantees that it // is in this list. The pointers are in the right order. Some(unsafe { self.remove_internal_inner(item, next, prev) }) } else { None } } /// Removes the provided item from the list. /// /// # Safety /// /// `item` must point at an item in this list. unsafe fn remove_internal(&mut self, item: *mut ListLinksFields) -> ListArc<T, ID> { // SAFETY: The caller promises that this pointer is not dangling, and there's no data race // since we have a mutable reference to the list containing `item`. let ListLinksFields { next, prev } = unsafe { *item }; // SAFETY: The pointers are ok and in the right order. unsafe { self.remove_internal_inner(item, next, prev) } } /// Removes the provided item from the list. /// /// # Safety /// /// The `item` pointer must point at an item in this list, and we must have `(*item).next == /// next` and `(*item).prev == prev`. unsafe fn remove_internal_inner( &mut self, item: *mut ListLinksFields, next: *mut ListLinksFields, prev: *mut ListLinksFields, ) -> ListArc<T, ID> { // SAFETY: We have exclusive access to the pointers of items in the list, and the prev/next // pointers are always valid for items in a list. // // INVARIANT: There are three cases: // * If the list has at least three items, then after removing the item, `prev` and `next` // will be next to each other. // * If the list has two items, then the remaining item will point at itself. // * If the list has one item, then `next == prev == item`, so these writes have no // effect. The list remains unchanged and `item` is still in the list for now. unsafe { (*next).prev = prev; (*prev).next = next; } // SAFETY: We have exclusive access to items in the list. // INVARIANT: `item` is being removed, so the pointers should be null. unsafe { (*item).prev = ptr::null_mut(); (*item).next = ptr::null_mut(); } // INVARIANT: There are three cases: // * If `item` was not the first item, then `self.first` should remain unchanged. // * If `item` was the first item and there is another item, then we just updated // `prev->next` to `next`, which is the new first item, and setting `item->next` to null // did not modify `prev->next`. // * If `item` was the only item in the list, then `prev == item`, and we just set // `item->next` to null, so this correctly sets `first` to null now that the list is // empty. if self.first == item { // SAFETY: The `prev` pointer is the value that `item->prev` had when it was in this // list, so it must be valid. There is no race since `prev` is still in the list and we // still have exclusive access to the list. self.first = unsafe { (*prev).next }; } // SAFETY: `item` used to be in the list, so it is dereferenceable by the type invariants // of `List`. let list_links = unsafe { ListLinks::from_fields(item) }; // SAFETY: Any pointer in the list originates from a `prepare_to_insert` call. let raw_item = unsafe { T::post_remove(list_links) }; // SAFETY: The above call to `post_remove` guarantees that we can recreate the `ListArc`. unsafe { ListArc::from_raw(raw_item) } } /// Moves all items from `other` into `self`. /// /// The items of `other` are added to the back of `self`, so the last item of `other` becomes /// the last item of `self`. pub fn push_all_back(&mut self, other: &mut List<T, ID>) { // First, we insert the elements into `self`. At the end, we make `other` empty. if self.is_empty() { // INVARIANT: All of the elements in `other` become elements of `self`. self.first = other.first; } else if !other.is_empty() { let other_first = other.first; // SAFETY: The other list is not empty, so this pointer is valid. let other_last = unsafe { (*other_first).prev }; let self_first = self.first; // SAFETY: The self list is not empty, so this pointer is valid. let self_last = unsafe { (*self_first).prev }; // SAFETY: We have exclusive access to both lists, so we can update the pointers. // INVARIANT: This correctly sets the pointers to merge both lists. We do not need to // update `self.first` because the first element of `self` does not change. unsafe { (*self_first).prev = other_last; (*other_last).next = self_first; (*self_last).next = other_first; (*other_first).prev = self_last; } } // INVARIANT: The other list is now empty, so update its pointer. other.first = ptr::null_mut(); } /// Returns a cursor that points before the first element of the list. pub fn cursor_front(&mut self) -> Cursor<'_, T, ID> { // INVARIANT: `self.first` is in this list. Cursor { next: self.first, list: self, } } /// Returns a cursor that points after the last element in the list. pub fn cursor_back(&mut self) -> Cursor<'_, T, ID> { // INVARIANT: `next` is allowed to be null.Lines 1–500 of 977. Load more
// SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2024 Google LLC. //! A linked list implementation. // May not be needed in Rust 1.87.0 (pending beta backport). #![allow(clippy::ptr_eq)] use crate::sync::ArcBorrow; use crate::types::Opaque; use core::iter::{DoubleEndedIterator, FusedIterator}; use core::marker::PhantomData; use core::ptr; use pin_init::PinInit; mod impl_list_item_mod; pub use self::impl_list_item_mod::{ impl_has_list_links, impl_has_list_links_self_ptr, impl_list_item, HasListLinks, HasSelfPtr, }; mod arc; pub use self::arc::{impl_list_arc_safe, AtomicTracker, ListArc, ListArcSafe, TryNewListArc}; mod arc_field; pub use self::arc_field::{define_list_arc_field_getter, ListArcField}; /// A linked list. /// /// All elements in this linked list will be [`ListArc`] references to the value. Since a value can /// only have one `ListArc` (for each pair of prev/next pointers), this ensures that the same /// prev/next pointers are not used for several linked lists. /// /// # Invariants /// /// * If the list is empty, then `first` is null. Otherwise, `first` points at the `ListLinks` /// field of the first element in the list. /// * All prev/next pointers in `ListLinks` fields of items in the list are valid and form a cycle. /// * For every item in the list, the list owns the associated [`ListArc`] reference and has /// exclusive access to the `ListLinks` field. pub struct List<T: ?Sized + ListItem<ID>, const ID: u64 = 0> { first: *mut ListLinksFields, _ty: PhantomData<ListArc<T, ID>>, } // SAFETY: This is a container of `ListArc<T, ID>`, and access to the container allows the same // type of access to the `ListArc<T, ID>` elements. unsafe impl<T, const ID: u64> Send for List<T, ID> where ListArc<T, ID>: Send, T: ?Sized + ListItem<ID>, { } // SAFETY: This is a container of `ListArc<T, ID>`, and access to the container allows the same // type of access to the `ListArc<T, ID>` elements. unsafe impl<T, const ID: u64> Sync for List<T, ID> where ListArc<T, ID>: Sync, T: ?Sized + ListItem<ID>, { } /// Implemented by types where a [`ListArc<Self>`] can be inserted into a [`List`]. /// /// # Safety /// /// Implementers must ensure that they provide the guarantees documented on methods provided by /// this trait. /// /// [`ListArc<Self>`]: ListArc pub unsafe trait ListItem<const ID: u64 = 0>: ListArcSafe<ID> { /// Views the [`ListLinks`] for this value. /// /// # Guarantees /// /// If there is a previous call to `prepare_to_insert` and there is no call to `post_remove` /// since the most recent such call, then this returns the same pointer as the one returned by /// the most recent call to `prepare_to_insert`. /// /// Otherwise, the returned pointer points at a read-only [`ListLinks`] with two null pointers. /// /// # Safety /// /// The provided pointer must point at a valid value. (It need not be in an `Arc`.) unsafe fn view_links(me: *const Self) -> *mut ListLinks<ID>; /// View the full value given its [`ListLinks`] field. /// /// Can only be used when the value is in a list. /// /// # Guarantees /// /// * Returns the same pointer as the one passed to the most recent call to `prepare_to_insert`. /// * The returned pointer is valid until the next call to `post_remove`. /// /// # Safety /// /// * The provided pointer must originate from the most recent call to `prepare_to_insert`, or /// from a call to `view_links` that happened after the most recent call to /// `prepare_to_insert`. /// * Since the most recent call to `prepare_to_insert`, the `post_remove` method must not have /// been called. unsafe fn view_value(me: *mut ListLinks<ID>) -> *const Self; /// This is called when an item is inserted into a [`List`]. /// /// # Guarantees /// /// The caller is granted exclusive access to the returned [`ListLinks`] until `post_remove` is /// called. /// /// # Safety /// /// * The provided pointer must point at a valid value in an [`Arc`]. /// * Calls to `prepare_to_insert` and `post_remove` on the same value must alternate. /// * The caller must own the [`ListArc`] for this value. /// * The caller must not give up ownership of the [`ListArc`] unless `post_remove` has been /// called after this call to `prepare_to_insert`. /// /// [`Arc`]: crate::sync::Arc unsafe fn prepare_to_insert(me: *const Self) -> *mut ListLinks<ID>; /// This undoes a previous call to `prepare_to_insert`. /// /// # Guarantees /// /// The returned pointer is the pointer that was originally passed to `prepare_to_insert`. /// /// # Safety /// /// The provided pointer must be the pointer returned by the most recent call to /// `prepare_to_insert`. unsafe fn post_remove(me: *mut ListLinks<ID>) -> *const Self; } #[repr(C)] #[derive(Copy, Clone)] struct ListLinksFields { next: *mut ListLinksFields, prev: *mut ListLinksFields, } /// The prev/next pointers for an item in a linked list. /// /// # Invariants /// /// The fields are null if and only if this item is not in a list. #[repr(transparent)] pub struct ListLinks<const ID: u64 = 0> { // This type is `!Unpin` for aliasing reasons as the pointers are part of an intrusive linked // list. inner: Opaque<ListLinksFields>, } // SAFETY: The only way to access/modify the pointers inside of `ListLinks<ID>` is via holding the // associated `ListArc<T, ID>`. Since that type correctly implements `Send`, it is impossible to // move this an instance of this type to a different thread if the pointees are `!Send`. unsafe impl<const ID: u64> Send for ListLinks<ID> {} // SAFETY: The type is opaque so immutable references to a ListLinks are useless. Therefore, it's // okay to have immutable access to a ListLinks from several threads at once. unsafe impl<const ID: u64> Sync for ListLinks<ID> {} impl<const ID: u64> ListLinks<ID> { /// Creates a new initializer for this type. pub fn new() -> impl PinInit<Self> { // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will // not be constructed in an `Arc` that already has a `ListArc`. ListLinks { inner: Opaque::new(ListLinksFields { prev: ptr::null_mut(), next: ptr::null_mut(), }), } } /// # Safety /// /// `me` must be dereferenceable. #[inline] unsafe fn fields(me: *mut Self) -> *mut ListLinksFields { // SAFETY: The caller promises that the pointer is valid. unsafe { Opaque::raw_get(ptr::addr_of!((*me).inner)) } } /// # Safety /// /// `me` must be dereferenceable. #[inline] unsafe fn from_fields(me: *mut ListLinksFields) -> *mut Self { me.cast() } } /// Similar to [`ListLinks`], but also contains a pointer to the full value. /// /// This type can be used instead of [`ListLinks`] to support lists with trait objects. #[repr(C)] pub struct ListLinksSelfPtr<T: ?Sized, const ID: u64 = 0> { /// The `ListLinks` field inside this value. /// /// This is public so that it can be used with `impl_has_list_links!`. pub inner: ListLinks<ID>, // UnsafeCell is not enough here because we use `Opaque::uninit` as a dummy value, and // `ptr::null()` doesn't work for `T: ?Sized`. self_ptr: Opaque<*const T>, } // SAFETY: The fields of a ListLinksSelfPtr can be moved across thread boundaries. unsafe impl<T: ?Sized + Send, const ID: u64> Send for ListLinksSelfPtr<T, ID> {} // SAFETY: The type is opaque so immutable references to a ListLinksSelfPtr are useless. Therefore, // it's okay to have immutable access to a ListLinks from several threads at once. // // Note that `inner` being a public field does not prevent this type from being opaque, since // `inner` is a opaque type. unsafe impl<T: ?Sized + Sync, const ID: u64> Sync for ListLinksSelfPtr<T, ID> {} impl<T: ?Sized, const ID: u64> ListLinksSelfPtr<T, ID> { /// The offset from the [`ListLinks`] to the self pointer field. pub const LIST_LINKS_SELF_PTR_OFFSET: usize = core::mem::offset_of!(Self, self_ptr); /// Creates a new initializer for this type. pub fn new() -> impl PinInit<Self> { // INVARIANT: Pin-init initializers can't be used on an existing `Arc`, so this value will // not be constructed in an `Arc` that already has a `ListArc`. Self { inner: ListLinks { inner: Opaque::new(ListLinksFields { prev: ptr::null_mut(), next: ptr::null_mut(), }), }, self_ptr: Opaque::uninit(), } } } impl<T: ?Sized + ListItem<ID>, const ID: u64> List<T, ID> { /// Creates a new empty list. pub const fn new() -> Self { Self { first: ptr::null_mut(), _ty: PhantomData, } } /// Returns whether this list is empty. pub fn is_empty(&self) -> bool { self.first.is_null() } /// Inserts `item` before `next` in the cycle. /// /// Returns a pointer to the newly inserted element. Never changes `self.first` unless the list /// is empty. /// /// # Safety /// /// * `next` must be an element in this list or null. /// * if `next` is null, then the list must be empty. unsafe fn insert_inner( &mut self, item: ListArc<T, ID>, next: *mut ListLinksFields, ) -> *mut ListLinksFields { let raw_item = ListArc::into_raw(item); // SAFETY: // * We just got `raw_item` from a `ListArc`, so it's in an `Arc`. // * Since we have ownership of the `ListArc`, `post_remove` must have been called after // the most recent call to `prepare_to_insert`, if any. // * We own the `ListArc`. // * Removing items from this list is always done using `remove_internal_inner`, which // calls `post_remove` before giving up ownership. let list_links = unsafe { T::prepare_to_insert(raw_item) }; // SAFETY: We have not yet called `post_remove`, so `list_links` is still valid. let item = unsafe { ListLinks::fields(list_links) }; // Check if the list is empty. if next.is_null() { // SAFETY: The caller just gave us ownership of these fields. // INVARIANT: A linked list with one item should be cyclic. unsafe { (*item).next = item; (*item).prev = item; } self.first = item; } else { // SAFETY: By the type invariant, this pointer is valid or null. We just checked that // it's not null, so it must be valid. let prev = unsafe { (*next).prev }; // SAFETY: Pointers in a linked list are never dangling, and the caller just gave us // ownership of the fields on `item`. // INVARIANT: This correctly inserts `item` between `prev` and `next`. unsafe { (*item).next = next; (*item).prev = prev; (*prev).next = item; (*next).prev = item; } } item } /// Add the provided item to the back of the list. pub fn push_back(&mut self, item: ListArc<T, ID>) { // SAFETY: // * `self.first` is null or in the list. // * `self.first` is only null if the list is empty. unsafe { self.insert_inner(item, self.first) }; } /// Add the provided item to the front of the list. pub fn push_front(&mut self, item: ListArc<T, ID>) { // SAFETY: // * `self.first` is null or in the list. // * `self.first` is only null if the list is empty. let new_elem = unsafe { self.insert_inner(item, self.first) }; // INVARIANT: `new_elem` is in the list because we just inserted it. self.first = new_elem; } /// Removes the last item from this list. pub fn pop_back(&mut self) -> Option<ListArc<T, ID>> { if self.first.is_null() { return None; } // SAFETY: We just checked that the list is not empty. let last = unsafe { (*self.first).prev }; // SAFETY: The last item of this list is in this list. Some(unsafe { self.remove_internal(last) }) } /// Removes the first item from this list. pub fn pop_front(&mut self) -> Option<ListArc<T, ID>> { if self.first.is_null() { return None; } // SAFETY: The first item of this list is in this list. Some(unsafe { self.remove_internal(self.first) }) } /// Removes the provided item from this list and returns it. /// /// This returns `None` if the item is not in the list. (Note that by the safety requirements, /// this means that the item is not in any list.) /// /// # Safety /// /// `item` must not be in a different linked list (with the same id). pub unsafe fn remove(&mut self, item: &T) -> Option<ListArc<T, ID>> { // SAFETY: TODO. let mut item = unsafe { ListLinks::fields(T::view_links(item)) }; // SAFETY: The user provided a reference, and reference are never dangling. // // As for why this is not a data race, there are two cases: // // * If `item` is not in any list, then these fields are read-only and null. // * If `item` is in this list, then we have exclusive access to these fields since we // have a mutable reference to the list. // // In either case, there's no race. let ListLinksFields { next, prev } = unsafe { *item }; debug_assert_eq!(next.is_null(), prev.is_null()); if !next.is_null() { // This is really a no-op, but this ensures that `item` is a raw pointer that was // obtained without going through a pointer->reference->pointer conversion roundtrip. // This ensures that the list is valid under the more restrictive strict provenance // ruleset. // // SAFETY: We just checked that `next` is not null, and it's not dangling by the // list invariants. unsafe { debug_assert_eq!(item, (*next).prev); item = (*next).prev; } // SAFETY: We just checked that `item` is in a list, so the caller guarantees that it // is in this list. The pointers are in the right order. Some(unsafe { self.remove_internal_inner(item, next, prev) }) } else { None } } /// Removes the provided item from the list. /// /// # Safety /// /// `item` must point at an item in this list. unsafe fn remove_internal(&mut self, item: *mut ListLinksFields) -> ListArc<T, ID> { // SAFETY: The caller promises that this pointer is not dangling, and there's no data race // since we have a mutable reference to the list containing `item`. let ListLinksFields { next, prev } = unsafe { *item }; // SAFETY: The pointers are ok and in the right order. unsafe { self.remove_internal_inner(item, next, prev) } } /// Removes the provided item from the list. /// /// # Safety /// /// The `item` pointer must point at an item in this list, and we must have `(*item).next == /// next` and `(*item).prev == prev`. unsafe fn remove_internal_inner( &mut self, item: *mut ListLinksFields, next: *mut ListLinksFields, prev: *mut ListLinksFields, ) -> ListArc<T, ID> { // SAFETY: We have exclusive access to the pointers of items in the list, and the prev/next // pointers are always valid for items in a list. // // INVARIANT: There are three cases: // * If the list has at least three items, then after removing the item, `prev` and `next` // will be next to each other. // * If the list has two items, then the remaining item will point at itself. // * If the list has one item, then `next == prev == item`, so these writes have no // effect. The list remains unchanged and `item` is still in the list for now. unsafe { (*next).prev = prev; (*prev).next = next; } // SAFETY: We have exclusive access to items in the list. // INVARIANT: `item` is being removed, so the pointers should be null. unsafe { (*item).prev = ptr::null_mut(); (*item).next = ptr::null_mut(); } // INVARIANT: There are three cases: // * If `item` was not the first item, then `self.first` should remain unchanged. // * If `item` was the first item and there is another item, then we just updated // `prev->next` to `next`, which is the new first item, and setting `item->next` to null // did not modify `prev->next`. // * If `item` was the only item in the list, then `prev == item`, and we just set // `item->next` to null, so this correctly sets `first` to null now that the list is // empty. if self.first == item { // SAFETY: The `prev` pointer is the value that `item->prev` had when it was in this // list, so it must be valid. There is no race since `prev` is still in the list and we // still have exclusive access to the list. self.first = unsafe { (*prev).next }; } // SAFETY: `item` used to be in the list, so it is dereferenceable by the type invariants // of `List`. let list_links = unsafe { ListLinks::from_fields(item) }; // SAFETY: Any pointer in the list originates from a `prepare_to_insert` call. let raw_item = unsafe { T::post_remove(list_links) }; // SAFETY: The above call to `post_remove` guarantees that we can recreate the `ListArc`. unsafe { ListArc::from_raw(raw_item) } } /// Moves all items from `other` into `self`. /// /// The items of `other` are added to the back of `self`, so the last item of `other` becomes /// the last item of `self`. pub fn push_all_back(&mut self, other: &mut List<T, ID>) { // First, we insert the elements into `self`. At the end, we make `other` empty. if self.is_empty() { // INVARIANT: All of the elements in `other` become elements of `self`. self.first = other.first; } else if !other.is_empty() { let other_first = other.first; // SAFETY: The other list is not empty, so this pointer is valid. let other_last = unsafe { (*other_first).prev }; let self_first = self.first; // SAFETY: The self list is not empty, so this pointer is valid. let self_last = unsafe { (*self_first).prev }; // SAFETY: We have exclusive access to both lists, so we can update the pointers. // INVARIANT: This correctly sets the pointers to merge both lists. We do not need to // update `self.first` because the first element of `self` does not change. unsafe { (*self_first).prev = other_last; (*other_last).next = self_first; (*self_last).next = other_first; (*other_first).prev = self_last; } } // INVARIANT: The other list is now empty, so update its pointer. other.first = ptr::null_mut(); } /// Returns a cursor that points before the first element of the list. pub fn cursor_front(&mut self) -> Cursor<'_, T, ID> { // INVARIANT: `self.first` is in this list. Cursor { next: self.first, list: self, } } /// Returns a cursor that points after the last element in the list. pub fn cursor_back(&mut self) -> Cursor<'_, T, ID> { // INVARIANT: `next` is allowed to be null.