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2211 lines
69 KiB
Rust
2211 lines
69 KiB
Rust
//! Single-threaded reference-counting pointers. 'Rc' stands for 'Reference
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//! Counted'.
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//!
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//! The type [`Rc<T>`][`Rc`] provides shared ownership of a value of type `T`,
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//! allocated in the heap. Invoking [`clone`][clone] on [`Rc`] produces a new
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//! pointer to the same allocation in the heap. When the last [`Rc`] pointer to a
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//! given allocation is destroyed, the value stored in that allocation (often
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//! referred to as "inner value") is also dropped.
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//!
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//! Shared references in Rust disallow mutation by default, and [`Rc`]
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//! is no exception: you cannot generally obtain a mutable reference to
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//! something inside an [`Rc`]. If you need mutability, put a [`Cell`]
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//! or [`RefCell`] inside the [`Rc`]; see [an example of mutability
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//! inside an Rc][mutability].
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//!
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//! [`Rc`] uses non-atomic reference counting. This means that overhead is very
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//! low, but an [`Rc`] cannot be sent between threads, and consequently [`Rc`]
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//! does not implement [`Send`][send]. As a result, the Rust compiler
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//! will check *at compile time* that you are not sending [`Rc`]s between
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//! threads. If you need multi-threaded, atomic reference counting, use
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//! [`sync::Arc`][arc].
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//!
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//! The [`downgrade`][downgrade] method can be used to create a non-owning
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//! [`Weak`] pointer. A [`Weak`] pointer can be [`upgrade`][upgrade]d
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//! to an [`Rc`], but this will return [`None`] if the value stored in the allocation has
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//! already been dropped. In other words, `Weak` pointers do not keep the value
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//! inside the allocation alive; however, they *do* keep the allocation
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//! (the backing store for the inner value) alive.
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//!
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//! A cycle between [`Rc`] pointers will never be deallocated. For this reason,
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//! [`Weak`] is used to break cycles. For example, a tree could have strong
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//! [`Rc`] pointers from parent nodes to children, and [`Weak`] pointers from
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//! children back to their parents.
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//!
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//! `Rc<T>` automatically dereferences to `T` (via the [`Deref`] trait),
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//! so you can call `T`'s methods on a value of type [`Rc<T>`][`Rc`]. To avoid name
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//! clashes with `T`'s methods, the methods of [`Rc<T>`][`Rc`] itself are associated
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//! functions, called using function-like syntax:
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//!
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//! ```
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//! use std::rc::Rc;
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//! let my_rc = Rc::new(());
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//!
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//! Rc::downgrade(&my_rc);
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//! ```
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//!
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//! [`Weak<T>`][`Weak`] does not auto-dereference to `T`, because the inner value may have
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//! already been dropped.
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//!
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//! # Cloning references
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//!
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//! Creating a new reference to the same allocation as an existing reference counted pointer
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//! is done using the `Clone` trait implemented for [`Rc<T>`][`Rc`] and [`Weak<T>`][`Weak`].
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//!
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//! ```
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//! use std::rc::Rc;
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//! let foo = Rc::new(vec![1.0, 2.0, 3.0]);
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//! // The two syntaxes below are equivalent.
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//! let a = foo.clone();
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//! let b = Rc::clone(&foo);
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//! // a and b both point to the same memory location as foo.
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//! ```
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//!
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//! The `Rc::clone(&from)` syntax is the most idiomatic because it conveys more explicitly
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//! the meaning of the code. In the example above, this syntax makes it easier to see that
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//! this code is creating a new reference rather than copying the whole content of foo.
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//!
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//! # Examples
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//!
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//! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
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//! We want to have our `Gadget`s point to their `Owner`. We can't do this with
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//! unique ownership, because more than one gadget may belong to the same
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//! `Owner`. [`Rc`] allows us to share an `Owner` between multiple `Gadget`s,
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//! and have the `Owner` remain allocated as long as any `Gadget` points at it.
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//!
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//! ```
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//! use std::rc::Rc;
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//!
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//! struct Owner {
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//! name: String,
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//! // ...other fields
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//! }
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//!
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//! struct Gadget {
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//! id: i32,
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//! owner: Rc<Owner>,
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//! // ...other fields
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//! }
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//!
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//! fn main() {
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//! // Create a reference-counted `Owner`.
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//! let gadget_owner: Rc<Owner> = Rc::new(
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//! Owner {
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//! name: "Gadget Man".to_string(),
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//! }
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//! );
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//!
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//! // Create `Gadget`s belonging to `gadget_owner`. Cloning the `Rc<Owner>`
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//! // gives us a new pointer to the same `Owner` allocation, incrementing
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//! // the reference count in the process.
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//! let gadget1 = Gadget {
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//! id: 1,
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//! owner: Rc::clone(&gadget_owner),
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//! };
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//! let gadget2 = Gadget {
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//! id: 2,
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//! owner: Rc::clone(&gadget_owner),
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//! };
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//!
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//! // Dispose of our local variable `gadget_owner`.
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//! drop(gadget_owner);
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//!
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//! // Despite dropping `gadget_owner`, we're still able to print out the name
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//! // of the `Owner` of the `Gadget`s. This is because we've only dropped a
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//! // single `Rc<Owner>`, not the `Owner` it points to. As long as there are
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//! // other `Rc<Owner>` pointing at the same `Owner` allocation, it will remain
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//! // live. The field projection `gadget1.owner.name` works because
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//! // `Rc<Owner>` automatically dereferences to `Owner`.
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//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
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//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
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//!
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//! // At the end of the function, `gadget1` and `gadget2` are destroyed, and
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//! // with them the last counted references to our `Owner`. Gadget Man now
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//! // gets destroyed as well.
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//! }
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//! ```
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//!
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//! If our requirements change, and we also need to be able to traverse from
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//! `Owner` to `Gadget`, we will run into problems. An [`Rc`] pointer from `Owner`
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//! to `Gadget` introduces a cycle. This means that their
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//! reference counts can never reach 0, and the allocation will never be destroyed:
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//! a memory leak. In order to get around this, we can use [`Weak`]
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//! pointers.
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//!
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//! Rust actually makes it somewhat difficult to produce this loop in the first
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//! place. In order to end up with two values that point at each other, one of
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//! them needs to be mutable. This is difficult because [`Rc`] enforces
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//! memory safety by only giving out shared references to the value it wraps,
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//! and these don't allow direct mutation. We need to wrap the part of the
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//! value we wish to mutate in a [`RefCell`], which provides *interior
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//! mutability*: a method to achieve mutability through a shared reference.
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//! [`RefCell`] enforces Rust's borrowing rules at runtime.
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//!
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//! ```
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//! use std::rc::Rc;
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//! use std::rc::Weak;
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//! use std::cell::RefCell;
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//!
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//! struct Owner {
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//! name: String,
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//! gadgets: RefCell<Vec<Weak<Gadget>>>,
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//! // ...other fields
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//! }
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//!
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//! struct Gadget {
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//! id: i32,
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//! owner: Rc<Owner>,
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//! // ...other fields
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//! }
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//!
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//! fn main() {
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//! // Create a reference-counted `Owner`. Note that we've put the `Owner`'s
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//! // vector of `Gadget`s inside a `RefCell` so that we can mutate it through
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//! // a shared reference.
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//! let gadget_owner: Rc<Owner> = Rc::new(
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//! Owner {
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//! name: "Gadget Man".to_string(),
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//! gadgets: RefCell::new(vec![]),
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//! }
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//! );
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//!
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//! // Create `Gadget`s belonging to `gadget_owner`, as before.
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//! let gadget1 = Rc::new(
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//! Gadget {
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//! id: 1,
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//! owner: Rc::clone(&gadget_owner),
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//! }
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//! );
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//! let gadget2 = Rc::new(
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//! Gadget {
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//! id: 2,
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//! owner: Rc::clone(&gadget_owner),
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//! }
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//! );
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//!
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//! // Add the `Gadget`s to their `Owner`.
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//! {
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//! let mut gadgets = gadget_owner.gadgets.borrow_mut();
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//! gadgets.push(Rc::downgrade(&gadget1));
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//! gadgets.push(Rc::downgrade(&gadget2));
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//!
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//! // `RefCell` dynamic borrow ends here.
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//! }
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//!
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//! // Iterate over our `Gadget`s, printing their details out.
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//! for gadget_weak in gadget_owner.gadgets.borrow().iter() {
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//!
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//! // `gadget_weak` is a `Weak<Gadget>`. Since `Weak` pointers can't
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//! // guarantee the allocation still exists, we need to call
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//! // `upgrade`, which returns an `Option<Rc<Gadget>>`.
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//! //
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//! // In this case we know the allocation still exists, so we simply
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//! // `unwrap` the `Option`. In a more complicated program, you might
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//! // need graceful error handling for a `None` result.
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//!
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//! let gadget = gadget_weak.upgrade().unwrap();
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//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
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//! }
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//!
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//! // At the end of the function, `gadget_owner`, `gadget1`, and `gadget2`
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//! // are destroyed. There are now no strong (`Rc`) pointers to the
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//! // gadgets, so they are destroyed. This zeroes the reference count on
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//! // Gadget Man, so he gets destroyed as well.
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//! }
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//! ```
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//!
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//! [clone]: Clone::clone
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//! [`Cell`]: core::cell::Cell
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//! [`RefCell`]: core::cell::RefCell
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//! [send]: core::marker::Send
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//! [arc]: ../../std/sync/struct.Arc.html
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//! [`Deref`]: core::ops::Deref
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//! [downgrade]: Rc::downgrade
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//! [upgrade]: Weak::upgrade
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//! [mutability]: core::cell#introducing-mutability-inside-of-something-immutable
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#![stable(feature = "rust1", since = "1.0.0")]
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#[cfg(not(test))]
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use crate::boxed::Box;
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#[cfg(test)]
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use std::boxed::Box;
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use core::any::Any;
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use core::borrow;
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use core::cell::Cell;
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use core::cmp::Ordering;
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use core::convert::{From, TryFrom};
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use core::fmt;
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use core::hash::{Hash, Hasher};
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use core::intrinsics::abort;
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use core::iter;
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use core::marker::{self, PhantomData, Unpin, Unsize};
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use core::mem::{self, align_of_val_raw, forget, size_of_val};
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use core::ops::{CoerceUnsized, Deref, DispatchFromDyn, Receiver};
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use core::pin::Pin;
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use core::ptr::{self, NonNull};
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use core::slice::from_raw_parts_mut;
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use crate::alloc::{box_free, handle_alloc_error, AllocErr, AllocRef, Global, Layout};
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use crate::borrow::{Cow, ToOwned};
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use crate::string::String;
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use crate::vec::Vec;
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#[cfg(test)]
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mod tests;
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// This is repr(C) to future-proof against possible field-reordering, which
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// would interfere with otherwise safe [into|from]_raw() of transmutable
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// inner types.
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#[repr(C)]
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struct RcBox<T: ?Sized> {
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strong: Cell<usize>,
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weak: Cell<usize>,
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value: T,
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}
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/// A single-threaded reference-counting pointer. 'Rc' stands for 'Reference
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/// Counted'.
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///
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/// See the [module-level documentation](./index.html) for more details.
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///
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/// The inherent methods of `Rc` are all associated functions, which means
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/// that you have to call them as e.g., [`Rc::get_mut(&mut value)`][get_mut] instead of
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/// `value.get_mut()`. This avoids conflicts with methods of the inner
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/// type `T`.
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///
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/// [get_mut]: #method.get_mut
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#[cfg_attr(not(test), rustc_diagnostic_item = "Rc")]
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#[stable(feature = "rust1", since = "1.0.0")]
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pub struct Rc<T: ?Sized> {
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ptr: NonNull<RcBox<T>>,
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phantom: PhantomData<RcBox<T>>,
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}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> !marker::Send for Rc<T> {}
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#[stable(feature = "rust1", since = "1.0.0")]
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impl<T: ?Sized> !marker::Sync for Rc<T> {}
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#[unstable(feature = "coerce_unsized", issue = "27732")]
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impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Rc<U>> for Rc<T> {}
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#[unstable(feature = "dispatch_from_dyn", issue = "none")]
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impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Rc<U>> for Rc<T> {}
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impl<T: ?Sized> Rc<T> {
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#[inline(always)]
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fn inner(&self) -> &RcBox<T> {
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// This unsafety is ok because while this Rc is alive we're guaranteed
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// that the inner pointer is valid.
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unsafe { self.ptr.as_ref() }
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}
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fn from_inner(ptr: NonNull<RcBox<T>>) -> Self {
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Self { ptr, phantom: PhantomData }
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}
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unsafe fn from_ptr(ptr: *mut RcBox<T>) -> Self {
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Self::from_inner(unsafe { NonNull::new_unchecked(ptr) })
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}
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}
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impl<T> Rc<T> {
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/// Constructs a new `Rc<T>`.
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///
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/// # Examples
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///
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/// ```
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/// use std::rc::Rc;
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///
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/// let five = Rc::new(5);
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/// ```
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#[stable(feature = "rust1", since = "1.0.0")]
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pub fn new(value: T) -> Rc<T> {
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// There is an implicit weak pointer owned by all the strong
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// pointers, which ensures that the weak destructor never frees
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// the allocation while the strong destructor is running, even
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// if the weak pointer is stored inside the strong one.
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Self::from_inner(
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Box::leak(box RcBox { strong: Cell::new(1), weak: Cell::new(1), value }).into(),
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)
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}
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/// Constructs a new `Rc<T>` using a weak reference to itself. Attempting
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/// to upgrade the weak reference before this function returns will result
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/// in a `None` value. However, the weak reference may be cloned freely and
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/// stored for use at a later time.
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#[unstable(feature = "arc_new_cyclic", issue = "75861")]
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pub fn new_cyclic(data_fn: impl FnOnce(&Weak<T>) -> T) -> Rc<T> {
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// Construct the inner in the "uninitialized" state with a single
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// weak reference.
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let uninit_ptr: NonNull<_> = Box::leak(box RcBox {
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strong: Cell::new(0),
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weak: Cell::new(1),
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value: mem::MaybeUninit::<T>::uninit(),
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})
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.into();
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let init_ptr: NonNull<RcBox<T>> = uninit_ptr.cast();
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let weak = Weak { ptr: init_ptr };
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// It's important we don't give up ownership of the weak pointer, or
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// else the memory might be freed by the time `data_fn` returns. If
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// we really wanted to pass ownership, we could create an additional
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// weak pointer for ourselves, but this would result in additional
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// updates to the weak reference count which might not be necessary
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// otherwise.
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let data = data_fn(&weak);
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unsafe {
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let inner = init_ptr.as_ptr();
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ptr::write(&raw mut (*inner).value, data);
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let prev_value = (*inner).strong.get();
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debug_assert_eq!(prev_value, 0, "No prior strong references should exist");
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(*inner).strong.set(1);
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}
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let strong = Rc::from_inner(init_ptr);
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// Strong references should collectively own a shared weak reference,
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// so don't run the destructor for our old weak reference.
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mem::forget(weak);
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strong
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}
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/// Constructs a new `Rc` with uninitialized contents.
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///
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/// # Examples
|
||
///
|
||
/// ```
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||
/// #![feature(new_uninit)]
|
||
/// #![feature(get_mut_unchecked)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
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/// let mut five = Rc::<u32>::new_uninit();
|
||
///
|
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/// let five = unsafe {
|
||
/// // Deferred initialization:
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/// Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);
|
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///
|
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/// five.assume_init()
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/// };
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///
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/// assert_eq!(*five, 5)
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/// ```
|
||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
pub fn new_uninit() -> Rc<mem::MaybeUninit<T>> {
|
||
unsafe {
|
||
Rc::from_ptr(Rc::allocate_for_layout(
|
||
Layout::new::<T>(),
|
||
|layout| Global.alloc(layout),
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|mem| mem as *mut RcBox<mem::MaybeUninit<T>>,
|
||
))
|
||
}
|
||
}
|
||
|
||
/// Constructs a new `Rc` with uninitialized contents, with the memory
|
||
/// being filled with `0` bytes.
|
||
///
|
||
/// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
|
||
/// incorrect usage of this method.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(new_uninit)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let zero = Rc::<u32>::new_zeroed();
|
||
/// let zero = unsafe { zero.assume_init() };
|
||
///
|
||
/// assert_eq!(*zero, 0)
|
||
/// ```
|
||
///
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||
/// [zeroed]: mem::MaybeUninit::zeroed
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||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
pub fn new_zeroed() -> Rc<mem::MaybeUninit<T>> {
|
||
unsafe {
|
||
Rc::from_ptr(Rc::allocate_for_layout(
|
||
Layout::new::<T>(),
|
||
|layout| Global.alloc_zeroed(layout),
|
||
|mem| mem as *mut RcBox<mem::MaybeUninit<T>>,
|
||
))
|
||
}
|
||
}
|
||
|
||
/// Constructs a new `Pin<Rc<T>>`. If `T` does not implement `Unpin`, then
|
||
/// `value` will be pinned in memory and unable to be moved.
|
||
#[stable(feature = "pin", since = "1.33.0")]
|
||
pub fn pin(value: T) -> Pin<Rc<T>> {
|
||
unsafe { Pin::new_unchecked(Rc::new(value)) }
|
||
}
|
||
|
||
/// Returns the inner value, if the `Rc` has exactly one strong reference.
|
||
///
|
||
/// Otherwise, an [`Err`] is returned with the same `Rc` that was
|
||
/// passed in.
|
||
///
|
||
/// This will succeed even if there are outstanding weak references.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new(3);
|
||
/// assert_eq!(Rc::try_unwrap(x), Ok(3));
|
||
///
|
||
/// let x = Rc::new(4);
|
||
/// let _y = Rc::clone(&x);
|
||
/// assert_eq!(*Rc::try_unwrap(x).unwrap_err(), 4);
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_unique", since = "1.4.0")]
|
||
pub fn try_unwrap(this: Self) -> Result<T, Self> {
|
||
if Rc::strong_count(&this) == 1 {
|
||
unsafe {
|
||
let val = ptr::read(&*this); // copy the contained object
|
||
|
||
// Indicate to Weaks that they can't be promoted by decrementing
|
||
// the strong count, and then remove the implicit "strong weak"
|
||
// pointer while also handling drop logic by just crafting a
|
||
// fake Weak.
|
||
this.inner().dec_strong();
|
||
let _weak = Weak { ptr: this.ptr };
|
||
forget(this);
|
||
Ok(val)
|
||
}
|
||
} else {
|
||
Err(this)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T> Rc<[T]> {
|
||
/// Constructs a new reference-counted slice with uninitialized contents.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(new_uninit)]
|
||
/// #![feature(get_mut_unchecked)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut values = Rc::<[u32]>::new_uninit_slice(3);
|
||
///
|
||
/// let values = unsafe {
|
||
/// // Deferred initialization:
|
||
/// Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1);
|
||
/// Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2);
|
||
/// Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3);
|
||
///
|
||
/// values.assume_init()
|
||
/// };
|
||
///
|
||
/// assert_eq!(*values, [1, 2, 3])
|
||
/// ```
|
||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
pub fn new_uninit_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
|
||
unsafe { Rc::from_ptr(Rc::allocate_for_slice(len)) }
|
||
}
|
||
|
||
/// Constructs a new reference-counted slice with uninitialized contents, with the memory being
|
||
/// filled with `0` bytes.
|
||
///
|
||
/// See [`MaybeUninit::zeroed`][zeroed] for examples of correct and
|
||
/// incorrect usage of this method.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(new_uninit)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let values = Rc::<[u32]>::new_zeroed_slice(3);
|
||
/// let values = unsafe { values.assume_init() };
|
||
///
|
||
/// assert_eq!(*values, [0, 0, 0])
|
||
/// ```
|
||
///
|
||
/// [zeroed]: mem::MaybeUninit::zeroed
|
||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
pub fn new_zeroed_slice(len: usize) -> Rc<[mem::MaybeUninit<T>]> {
|
||
unsafe {
|
||
Rc::from_ptr(Rc::allocate_for_layout(
|
||
Layout::array::<T>(len).unwrap(),
|
||
|layout| Global.alloc_zeroed(layout),
|
||
|mem| {
|
||
ptr::slice_from_raw_parts_mut(mem as *mut T, len)
|
||
as *mut RcBox<[mem::MaybeUninit<T>]>
|
||
},
|
||
))
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T> Rc<mem::MaybeUninit<T>> {
|
||
/// Converts to `Rc<T>`.
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// As with [`MaybeUninit::assume_init`],
|
||
/// it is up to the caller to guarantee that the inner value
|
||
/// really is in an initialized state.
|
||
/// Calling this when the content is not yet fully initialized
|
||
/// causes immediate undefined behavior.
|
||
///
|
||
/// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(new_uninit)]
|
||
/// #![feature(get_mut_unchecked)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut five = Rc::<u32>::new_uninit();
|
||
///
|
||
/// let five = unsafe {
|
||
/// // Deferred initialization:
|
||
/// Rc::get_mut_unchecked(&mut five).as_mut_ptr().write(5);
|
||
///
|
||
/// five.assume_init()
|
||
/// };
|
||
///
|
||
/// assert_eq!(*five, 5)
|
||
/// ```
|
||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
#[inline]
|
||
pub unsafe fn assume_init(self) -> Rc<T> {
|
||
Rc::from_inner(mem::ManuallyDrop::new(self).ptr.cast())
|
||
}
|
||
}
|
||
|
||
impl<T> Rc<[mem::MaybeUninit<T>]> {
|
||
/// Converts to `Rc<[T]>`.
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// As with [`MaybeUninit::assume_init`],
|
||
/// it is up to the caller to guarantee that the inner value
|
||
/// really is in an initialized state.
|
||
/// Calling this when the content is not yet fully initialized
|
||
/// causes immediate undefined behavior.
|
||
///
|
||
/// [`MaybeUninit::assume_init`]: mem::MaybeUninit::assume_init
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(new_uninit)]
|
||
/// #![feature(get_mut_unchecked)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut values = Rc::<[u32]>::new_uninit_slice(3);
|
||
///
|
||
/// let values = unsafe {
|
||
/// // Deferred initialization:
|
||
/// Rc::get_mut_unchecked(&mut values)[0].as_mut_ptr().write(1);
|
||
/// Rc::get_mut_unchecked(&mut values)[1].as_mut_ptr().write(2);
|
||
/// Rc::get_mut_unchecked(&mut values)[2].as_mut_ptr().write(3);
|
||
///
|
||
/// values.assume_init()
|
||
/// };
|
||
///
|
||
/// assert_eq!(*values, [1, 2, 3])
|
||
/// ```
|
||
#[unstable(feature = "new_uninit", issue = "63291")]
|
||
#[inline]
|
||
pub unsafe fn assume_init(self) -> Rc<[T]> {
|
||
unsafe { Rc::from_ptr(mem::ManuallyDrop::new(self).ptr.as_ptr() as _) }
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> Rc<T> {
|
||
/// Consumes the `Rc`, returning the wrapped pointer.
|
||
///
|
||
/// To avoid a memory leak the pointer must be converted back to an `Rc` using
|
||
/// [`Rc::from_raw`][from_raw].
|
||
///
|
||
/// [from_raw]: Rc::from_raw
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new("hello".to_owned());
|
||
/// let x_ptr = Rc::into_raw(x);
|
||
/// assert_eq!(unsafe { &*x_ptr }, "hello");
|
||
/// ```
|
||
#[stable(feature = "rc_raw", since = "1.17.0")]
|
||
pub fn into_raw(this: Self) -> *const T {
|
||
let ptr = Self::as_ptr(&this);
|
||
mem::forget(this);
|
||
ptr
|
||
}
|
||
|
||
/// Provides a raw pointer to the data.
|
||
///
|
||
/// The counts are not affected in any way and the `Rc` is not consumed. The pointer is valid
|
||
/// for as long there are strong counts in the `Rc`.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new("hello".to_owned());
|
||
/// let y = Rc::clone(&x);
|
||
/// let x_ptr = Rc::as_ptr(&x);
|
||
/// assert_eq!(x_ptr, Rc::as_ptr(&y));
|
||
/// assert_eq!(unsafe { &*x_ptr }, "hello");
|
||
/// ```
|
||
#[stable(feature = "weak_into_raw", since = "1.45.0")]
|
||
pub fn as_ptr(this: &Self) -> *const T {
|
||
let ptr: *mut RcBox<T> = NonNull::as_ptr(this.ptr);
|
||
|
||
// SAFETY: This cannot go through Deref::deref or Rc::inner because
|
||
// this is required to retain raw/mut provenance such that e.g. `get_mut` can
|
||
// write through the pointer after the Rc is recovered through `from_raw`.
|
||
unsafe { &raw const (*ptr).value }
|
||
}
|
||
|
||
/// Constructs an `Rc<T>` from a raw pointer.
|
||
///
|
||
/// The raw pointer must have been previously returned by a call to
|
||
/// [`Rc<U>::into_raw`][into_raw] where `U` must have the same size
|
||
/// and alignment as `T`. This is trivially true if `U` is `T`.
|
||
/// Note that if `U` is not `T` but has the same size and alignment, this is
|
||
/// basically like transmuting references of different types. See
|
||
/// [`mem::transmute`][transmute] for more information on what
|
||
/// restrictions apply in this case.
|
||
///
|
||
/// 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 `Rc<T>` is never accessed.
|
||
///
|
||
/// [into_raw]: Rc::into_raw
|
||
/// [transmute]: core::mem::transmute
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x = Rc::new("hello".to_owned());
|
||
/// let x_ptr = Rc::into_raw(x);
|
||
///
|
||
/// unsafe {
|
||
/// // Convert back to an `Rc` to prevent leak.
|
||
/// let x = Rc::from_raw(x_ptr);
|
||
/// assert_eq!(&*x, "hello");
|
||
///
|
||
/// // Further calls to `Rc::from_raw(x_ptr)` would be memory-unsafe.
|
||
/// }
|
||
///
|
||
/// // The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!
|
||
/// ```
|
||
#[stable(feature = "rc_raw", since = "1.17.0")]
|
||
pub unsafe fn from_raw(ptr: *const T) -> Self {
|
||
let offset = unsafe { data_offset(ptr) };
|
||
|
||
// Reverse the offset to find the original RcBox.
|
||
let fake_ptr = ptr as *mut RcBox<T>;
|
||
let rc_ptr = unsafe { set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset)) };
|
||
|
||
unsafe { Self::from_ptr(rc_ptr) }
|
||
}
|
||
|
||
/// Creates a new [`Weak`] pointer to this allocation.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
/// ```
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub fn downgrade(this: &Self) -> Weak<T> {
|
||
this.inner().inc_weak();
|
||
// Make sure we do not create a dangling Weak
|
||
debug_assert!(!is_dangling(this.ptr));
|
||
Weak { ptr: this.ptr }
|
||
}
|
||
|
||
/// Gets the number of [`Weak`] pointers to this allocation.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let _weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// assert_eq!(1, Rc::weak_count(&five));
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_counts", since = "1.15.0")]
|
||
pub fn weak_count(this: &Self) -> usize {
|
||
this.inner().weak() - 1
|
||
}
|
||
|
||
/// Gets the number of strong (`Rc`) pointers to this allocation.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let _also_five = Rc::clone(&five);
|
||
///
|
||
/// assert_eq!(2, Rc::strong_count(&five));
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_counts", since = "1.15.0")]
|
||
pub fn strong_count(this: &Self) -> usize {
|
||
this.inner().strong()
|
||
}
|
||
|
||
/// Returns `true` if there are no other `Rc` or [`Weak`] pointers to
|
||
/// this allocation.
|
||
#[inline]
|
||
fn is_unique(this: &Self) -> bool {
|
||
Rc::weak_count(this) == 0 && Rc::strong_count(this) == 1
|
||
}
|
||
|
||
/// Returns a mutable reference into the given `Rc`, if there are
|
||
/// no other `Rc` or [`Weak`] pointers to the same allocation.
|
||
///
|
||
/// Returns [`None`] otherwise, because it is not safe to
|
||
/// mutate a shared value.
|
||
///
|
||
/// See also [`make_mut`][make_mut], which will [`clone`][clone]
|
||
/// the inner value when there are other pointers.
|
||
///
|
||
/// [make_mut]: Rc::make_mut
|
||
/// [clone]: Clone::clone
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut x = Rc::new(3);
|
||
/// *Rc::get_mut(&mut x).unwrap() = 4;
|
||
/// assert_eq!(*x, 4);
|
||
///
|
||
/// let _y = Rc::clone(&x);
|
||
/// assert!(Rc::get_mut(&mut x).is_none());
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_unique", since = "1.4.0")]
|
||
pub fn get_mut(this: &mut Self) -> Option<&mut T> {
|
||
if Rc::is_unique(this) { unsafe { Some(Rc::get_mut_unchecked(this)) } } else { None }
|
||
}
|
||
|
||
/// Returns a mutable reference into the given `Rc`,
|
||
/// without any check.
|
||
///
|
||
/// See also [`get_mut`], which is safe and does appropriate checks.
|
||
///
|
||
/// [`get_mut`]: Rc::get_mut
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// Any other `Rc` or [`Weak`] pointers to the same allocation must not be dereferenced
|
||
/// for the duration of the returned borrow.
|
||
/// This is trivially the case if no such pointers exist,
|
||
/// for example immediately after `Rc::new`.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// #![feature(get_mut_unchecked)]
|
||
///
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut x = Rc::new(String::new());
|
||
/// unsafe {
|
||
/// Rc::get_mut_unchecked(&mut x).push_str("foo")
|
||
/// }
|
||
/// assert_eq!(*x, "foo");
|
||
/// ```
|
||
#[inline]
|
||
#[unstable(feature = "get_mut_unchecked", issue = "63292")]
|
||
pub unsafe fn get_mut_unchecked(this: &mut Self) -> &mut T {
|
||
// We are careful to *not* create a reference covering the "count" fields, as
|
||
// this would conflict with accesses to the reference counts (e.g. by `Weak`).
|
||
unsafe { &mut (*this.ptr.as_ptr()).value }
|
||
}
|
||
|
||
#[inline]
|
||
#[stable(feature = "ptr_eq", since = "1.17.0")]
|
||
/// Returns `true` if the two `Rc`s point to the same allocation
|
||
/// (in a vein similar to [`ptr::eq`]).
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
/// let same_five = Rc::clone(&five);
|
||
/// let other_five = Rc::new(5);
|
||
///
|
||
/// assert!(Rc::ptr_eq(&five, &same_five));
|
||
/// assert!(!Rc::ptr_eq(&five, &other_five));
|
||
/// ```
|
||
///
|
||
/// [`ptr::eq`]: core::ptr::eq
|
||
pub fn ptr_eq(this: &Self, other: &Self) -> bool {
|
||
this.ptr.as_ptr() == other.ptr.as_ptr()
|
||
}
|
||
}
|
||
|
||
impl<T: Clone> Rc<T> {
|
||
/// Makes a mutable reference into the given `Rc`.
|
||
///
|
||
/// If there are other `Rc` pointers to the same allocation, then `make_mut` will
|
||
/// [`clone`] the inner value to a new allocation to ensure unique ownership. This is also
|
||
/// referred to as clone-on-write.
|
||
///
|
||
/// If there are no other `Rc` pointers to this allocation, then [`Weak`]
|
||
/// pointers to this allocation will be disassociated.
|
||
///
|
||
/// See also [`get_mut`], which will fail rather than cloning.
|
||
///
|
||
/// [`clone`]: Clone::clone
|
||
/// [`get_mut`]: Rc::get_mut
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut data = Rc::new(5);
|
||
///
|
||
/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
|
||
/// let mut other_data = Rc::clone(&data); // Won't clone inner data
|
||
/// *Rc::make_mut(&mut data) += 1; // Clones inner data
|
||
/// *Rc::make_mut(&mut data) += 1; // Won't clone anything
|
||
/// *Rc::make_mut(&mut other_data) *= 2; // Won't clone anything
|
||
///
|
||
/// // Now `data` and `other_data` point to different allocations.
|
||
/// assert_eq!(*data, 8);
|
||
/// assert_eq!(*other_data, 12);
|
||
/// ```
|
||
///
|
||
/// [`Weak`] pointers will be disassociated:
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let mut data = Rc::new(75);
|
||
/// let weak = Rc::downgrade(&data);
|
||
///
|
||
/// assert!(75 == *data);
|
||
/// assert!(75 == *weak.upgrade().unwrap());
|
||
///
|
||
/// *Rc::make_mut(&mut data) += 1;
|
||
///
|
||
/// assert!(76 == *data);
|
||
/// assert!(weak.upgrade().is_none());
|
||
/// ```
|
||
#[inline]
|
||
#[stable(feature = "rc_unique", since = "1.4.0")]
|
||
pub fn make_mut(this: &mut Self) -> &mut T {
|
||
if Rc::strong_count(this) != 1 {
|
||
// Gotta clone the data, there are other Rcs
|
||
*this = Rc::new((**this).clone())
|
||
} else if Rc::weak_count(this) != 0 {
|
||
// Can just steal the data, all that's left is Weaks
|
||
unsafe {
|
||
let mut swap = Rc::new(ptr::read(&this.ptr.as_ref().value));
|
||
mem::swap(this, &mut swap);
|
||
swap.inner().dec_strong();
|
||
// Remove implicit strong-weak ref (no need to craft a fake
|
||
// Weak here -- we know other Weaks can clean up for us)
|
||
swap.inner().dec_weak();
|
||
forget(swap);
|
||
}
|
||
}
|
||
// This unsafety is ok because we're guaranteed that the pointer
|
||
// returned is the *only* pointer that will ever be returned to T. Our
|
||
// reference count is guaranteed to be 1 at this point, and we required
|
||
// the `Rc<T>` itself to be `mut`, so we're returning the only possible
|
||
// reference to the allocation.
|
||
unsafe { &mut this.ptr.as_mut().value }
|
||
}
|
||
}
|
||
|
||
impl Rc<dyn Any> {
|
||
#[inline]
|
||
#[stable(feature = "rc_downcast", since = "1.29.0")]
|
||
/// Attempt to downcast the `Rc<dyn Any>` to a concrete type.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::any::Any;
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// fn print_if_string(value: Rc<dyn Any>) {
|
||
/// if let Ok(string) = value.downcast::<String>() {
|
||
/// println!("String ({}): {}", string.len(), string);
|
||
/// }
|
||
/// }
|
||
///
|
||
/// let my_string = "Hello World".to_string();
|
||
/// print_if_string(Rc::new(my_string));
|
||
/// print_if_string(Rc::new(0i8));
|
||
/// ```
|
||
pub fn downcast<T: Any>(self) -> Result<Rc<T>, Rc<dyn Any>> {
|
||
if (*self).is::<T>() {
|
||
let ptr = self.ptr.cast::<RcBox<T>>();
|
||
forget(self);
|
||
Ok(Rc::from_inner(ptr))
|
||
} else {
|
||
Err(self)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> Rc<T> {
|
||
/// Allocates an `RcBox<T>` with sufficient space for
|
||
/// a possibly-unsized inner value where the value has the layout provided.
|
||
///
|
||
/// The function `mem_to_rcbox` is called with the data pointer
|
||
/// and must return back a (potentially fat)-pointer for the `RcBox<T>`.
|
||
unsafe fn allocate_for_layout(
|
||
value_layout: Layout,
|
||
allocate: impl FnOnce(Layout) -> Result<NonNull<[u8]>, AllocErr>,
|
||
mem_to_rcbox: impl FnOnce(*mut u8) -> *mut RcBox<T>,
|
||
) -> *mut RcBox<T> {
|
||
// Calculate layout using the given value layout.
|
||
// Previously, layout was calculated on the expression
|
||
// `&*(ptr as *const RcBox<T>)`, but this created a misaligned
|
||
// reference (see #54908).
|
||
let layout = Layout::new::<RcBox<()>>().extend(value_layout).unwrap().0.pad_to_align();
|
||
|
||
// Allocate for the layout.
|
||
let ptr = allocate(layout).unwrap_or_else(|_| handle_alloc_error(layout));
|
||
|
||
// Initialize the RcBox
|
||
let inner = mem_to_rcbox(ptr.as_non_null_ptr().as_ptr());
|
||
unsafe {
|
||
debug_assert_eq!(Layout::for_value(&*inner), layout);
|
||
|
||
ptr::write(&mut (*inner).strong, Cell::new(1));
|
||
ptr::write(&mut (*inner).weak, Cell::new(1));
|
||
}
|
||
|
||
inner
|
||
}
|
||
|
||
/// Allocates an `RcBox<T>` with sufficient space for an unsized inner value
|
||
unsafe fn allocate_for_ptr(ptr: *const T) -> *mut RcBox<T> {
|
||
// Allocate for the `RcBox<T>` using the given value.
|
||
unsafe {
|
||
Self::allocate_for_layout(
|
||
Layout::for_value(&*ptr),
|
||
|layout| Global.alloc(layout),
|
||
|mem| set_data_ptr(ptr as *mut T, mem) as *mut RcBox<T>,
|
||
)
|
||
}
|
||
}
|
||
|
||
fn from_box(v: Box<T>) -> Rc<T> {
|
||
unsafe {
|
||
let box_unique = Box::into_unique(v);
|
||
let bptr = box_unique.as_ptr();
|
||
|
||
let value_size = size_of_val(&*bptr);
|
||
let ptr = Self::allocate_for_ptr(bptr);
|
||
|
||
// Copy value as bytes
|
||
ptr::copy_nonoverlapping(
|
||
bptr as *const T as *const u8,
|
||
&mut (*ptr).value as *mut _ as *mut u8,
|
||
value_size,
|
||
);
|
||
|
||
// Free the allocation without dropping its contents
|
||
box_free(box_unique);
|
||
|
||
Self::from_ptr(ptr)
|
||
}
|
||
}
|
||
}
|
||
|
||
impl<T> Rc<[T]> {
|
||
/// Allocates an `RcBox<[T]>` with the given length.
|
||
unsafe fn allocate_for_slice(len: usize) -> *mut RcBox<[T]> {
|
||
unsafe {
|
||
Self::allocate_for_layout(
|
||
Layout::array::<T>(len).unwrap(),
|
||
|layout| Global.alloc(layout),
|
||
|mem| ptr::slice_from_raw_parts_mut(mem as *mut T, len) as *mut RcBox<[T]>,
|
||
)
|
||
}
|
||
}
|
||
}
|
||
|
||
/// Sets the data pointer of a `?Sized` raw pointer.
|
||
///
|
||
/// For a slice/trait object, this sets the `data` field and leaves the rest
|
||
/// unchanged. For a sized raw pointer, this simply sets the pointer.
|
||
unsafe fn set_data_ptr<T: ?Sized, U>(mut ptr: *mut T, data: *mut U) -> *mut T {
|
||
unsafe {
|
||
ptr::write(&mut ptr as *mut _ as *mut *mut u8, data as *mut u8);
|
||
}
|
||
ptr
|
||
}
|
||
|
||
impl<T> Rc<[T]> {
|
||
/// Copy elements from slice into newly allocated Rc<\[T\]>
|
||
///
|
||
/// Unsafe because the caller must either take ownership or bind `T: Copy`
|
||
unsafe fn copy_from_slice(v: &[T]) -> Rc<[T]> {
|
||
unsafe {
|
||
let ptr = Self::allocate_for_slice(v.len());
|
||
ptr::copy_nonoverlapping(v.as_ptr(), &mut (*ptr).value as *mut [T] as *mut T, v.len());
|
||
Self::from_ptr(ptr)
|
||
}
|
||
}
|
||
|
||
/// Constructs an `Rc<[T]>` from an iterator known to be of a certain size.
|
||
///
|
||
/// Behavior is undefined should the size be wrong.
|
||
unsafe fn from_iter_exact(iter: impl iter::Iterator<Item = T>, len: usize) -> Rc<[T]> {
|
||
// Panic guard while cloning T elements.
|
||
// In the event of a panic, elements that have been written
|
||
// into the new RcBox will be dropped, then the memory freed.
|
||
struct Guard<T> {
|
||
mem: NonNull<u8>,
|
||
elems: *mut T,
|
||
layout: Layout,
|
||
n_elems: usize,
|
||
}
|
||
|
||
impl<T> Drop for Guard<T> {
|
||
fn drop(&mut self) {
|
||
unsafe {
|
||
let slice = from_raw_parts_mut(self.elems, self.n_elems);
|
||
ptr::drop_in_place(slice);
|
||
|
||
Global.dealloc(self.mem, self.layout);
|
||
}
|
||
}
|
||
}
|
||
|
||
unsafe {
|
||
let ptr = Self::allocate_for_slice(len);
|
||
|
||
let mem = ptr as *mut _ as *mut u8;
|
||
let layout = Layout::for_value(&*ptr);
|
||
|
||
// Pointer to first element
|
||
let elems = &mut (*ptr).value as *mut [T] as *mut T;
|
||
|
||
let mut guard = Guard { mem: NonNull::new_unchecked(mem), elems, layout, n_elems: 0 };
|
||
|
||
for (i, item) in iter.enumerate() {
|
||
ptr::write(elems.add(i), item);
|
||
guard.n_elems += 1;
|
||
}
|
||
|
||
// All clear. Forget the guard so it doesn't free the new RcBox.
|
||
forget(guard);
|
||
|
||
Self::from_ptr(ptr)
|
||
}
|
||
}
|
||
}
|
||
|
||
/// Specialization trait used for `From<&[T]>`.
|
||
trait RcFromSlice<T> {
|
||
fn from_slice(slice: &[T]) -> Self;
|
||
}
|
||
|
||
impl<T: Clone> RcFromSlice<T> for Rc<[T]> {
|
||
#[inline]
|
||
default fn from_slice(v: &[T]) -> Self {
|
||
unsafe { Self::from_iter_exact(v.iter().cloned(), v.len()) }
|
||
}
|
||
}
|
||
|
||
impl<T: Copy> RcFromSlice<T> for Rc<[T]> {
|
||
#[inline]
|
||
fn from_slice(v: &[T]) -> Self {
|
||
unsafe { Rc::copy_from_slice(v) }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Deref for Rc<T> {
|
||
type Target = T;
|
||
|
||
#[inline(always)]
|
||
fn deref(&self) -> &T {
|
||
&self.inner().value
|
||
}
|
||
}
|
||
|
||
#[unstable(feature = "receiver_trait", issue = "none")]
|
||
impl<T: ?Sized> Receiver for Rc<T> {}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
|
||
/// Drops the `Rc`.
|
||
///
|
||
/// This will decrement the strong reference count. If the strong reference
|
||
/// count reaches zero then the only other references (if any) are
|
||
/// [`Weak`], so we `drop` the inner value.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// struct Foo;
|
||
///
|
||
/// impl Drop for Foo {
|
||
/// fn drop(&mut self) {
|
||
/// println!("dropped!");
|
||
/// }
|
||
/// }
|
||
///
|
||
/// let foo = Rc::new(Foo);
|
||
/// let foo2 = Rc::clone(&foo);
|
||
///
|
||
/// drop(foo); // Doesn't print anything
|
||
/// drop(foo2); // Prints "dropped!"
|
||
/// ```
|
||
fn drop(&mut self) {
|
||
unsafe {
|
||
self.inner().dec_strong();
|
||
if self.inner().strong() == 0 {
|
||
// destroy the contained object
|
||
ptr::drop_in_place(Self::get_mut_unchecked(self));
|
||
|
||
// remove the implicit "strong weak" pointer now that we've
|
||
// destroyed the contents.
|
||
self.inner().dec_weak();
|
||
|
||
if self.inner().weak() == 0 {
|
||
Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
|
||
}
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> Clone for Rc<T> {
|
||
/// Makes a clone of the `Rc` pointer.
|
||
///
|
||
/// This creates another pointer to the same allocation, increasing the
|
||
/// strong reference count.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let _ = Rc::clone(&five);
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Rc<T> {
|
||
self.inner().inc_strong();
|
||
Self::from_inner(self.ptr)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: Default> Default for Rc<T> {
|
||
/// Creates a new `Rc<T>`, with the `Default` value for `T`.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let x: Rc<i32> = Default::default();
|
||
/// assert_eq!(*x, 0);
|
||
/// ```
|
||
#[inline]
|
||
fn default() -> Rc<T> {
|
||
Rc::new(Default::default())
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
trait RcEqIdent<T: ?Sized + PartialEq> {
|
||
fn eq(&self, other: &Rc<T>) -> bool;
|
||
fn ne(&self, other: &Rc<T>) -> bool;
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + PartialEq> RcEqIdent<T> for Rc<T> {
|
||
#[inline]
|
||
default fn eq(&self, other: &Rc<T>) -> bool {
|
||
**self == **other
|
||
}
|
||
|
||
#[inline]
|
||
default fn ne(&self, other: &Rc<T>) -> bool {
|
||
**self != **other
|
||
}
|
||
}
|
||
|
||
// Hack to allow specializing on `Eq` even though `Eq` has a method.
|
||
#[rustc_unsafe_specialization_marker]
|
||
pub(crate) trait MarkerEq: PartialEq<Self> {}
|
||
|
||
impl<T: Eq> MarkerEq for T {}
|
||
|
||
/// We're doing this specialization here, and not as a more general optimization on `&T`, because it
|
||
/// would otherwise add a cost to all equality checks on refs. We assume that `Rc`s are used to
|
||
/// store large values, that are slow to clone, but also heavy to check for equality, causing this
|
||
/// cost to pay off more easily. It's also more likely to have two `Rc` clones, that point to
|
||
/// the same value, than two `&T`s.
|
||
///
|
||
/// We can only do this when `T: Eq` as a `PartialEq` might be deliberately irreflexive.
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + MarkerEq> RcEqIdent<T> for Rc<T> {
|
||
#[inline]
|
||
fn eq(&self, other: &Rc<T>) -> bool {
|
||
Rc::ptr_eq(self, other) || **self == **other
|
||
}
|
||
|
||
#[inline]
|
||
fn ne(&self, other: &Rc<T>) -> bool {
|
||
!Rc::ptr_eq(self, other) && **self != **other
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
|
||
/// Equality for two `Rc`s.
|
||
///
|
||
/// Two `Rc`s are equal if their inner values are equal, even if they are
|
||
/// stored in different allocation.
|
||
///
|
||
/// If `T` also implements `Eq` (implying reflexivity of equality),
|
||
/// two `Rc`s that point to the same allocation are
|
||
/// always equal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five == Rc::new(5));
|
||
/// ```
|
||
#[inline]
|
||
fn eq(&self, other: &Rc<T>) -> bool {
|
||
RcEqIdent::eq(self, other)
|
||
}
|
||
|
||
/// Inequality for two `Rc`s.
|
||
///
|
||
/// Two `Rc`s are unequal if their inner values are unequal.
|
||
///
|
||
/// If `T` also implements `Eq` (implying reflexivity of equality),
|
||
/// two `Rc`s that point to the same allocation are
|
||
/// never unequal.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five != Rc::new(6));
|
||
/// ```
|
||
#[inline]
|
||
fn ne(&self, other: &Rc<T>) -> bool {
|
||
RcEqIdent::ne(self, other)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Eq> Eq for Rc<T> {}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + PartialOrd> PartialOrd for Rc<T> {
|
||
/// Partial comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `partial_cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
/// use std::cmp::Ordering;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert_eq!(Some(Ordering::Less), five.partial_cmp(&Rc::new(6)));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
|
||
(**self).partial_cmp(&**other)
|
||
}
|
||
|
||
/// Less-than comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `<` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five < Rc::new(6));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn lt(&self, other: &Rc<T>) -> bool {
|
||
**self < **other
|
||
}
|
||
|
||
/// 'Less than or equal to' comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `<=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five <= Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn le(&self, other: &Rc<T>) -> bool {
|
||
**self <= **other
|
||
}
|
||
|
||
/// Greater-than comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `>` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five > Rc::new(4));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn gt(&self, other: &Rc<T>) -> bool {
|
||
**self > **other
|
||
}
|
||
|
||
/// 'Greater than or equal to' comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `>=` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert!(five >= Rc::new(5));
|
||
/// ```
|
||
#[inline(always)]
|
||
fn ge(&self, other: &Rc<T>) -> bool {
|
||
**self >= **other
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Ord> Ord for Rc<T> {
|
||
/// Comparison for two `Rc`s.
|
||
///
|
||
/// The two are compared by calling `cmp()` on their inner values.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
/// use std::cmp::Ordering;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// assert_eq!(Ordering::Less, five.cmp(&Rc::new(6)));
|
||
/// ```
|
||
#[inline]
|
||
fn cmp(&self, other: &Rc<T>) -> Ordering {
|
||
(**self).cmp(&**other)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + Hash> Hash for Rc<T> {
|
||
fn hash<H: Hasher>(&self, state: &mut H) {
|
||
(**self).hash(state);
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + fmt::Display> fmt::Display for Rc<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
fmt::Display::fmt(&**self, f)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized + fmt::Debug> fmt::Debug for Rc<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
fmt::Debug::fmt(&**self, f)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> fmt::Pointer for Rc<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
fmt::Pointer::fmt(&(&**self as *const T), f)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "from_for_ptrs", since = "1.6.0")]
|
||
impl<T> From<T> for Rc<T> {
|
||
fn from(t: T) -> Self {
|
||
Rc::new(t)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<T: Clone> From<&[T]> for Rc<[T]> {
|
||
#[inline]
|
||
fn from(v: &[T]) -> Rc<[T]> {
|
||
<Self as RcFromSlice<T>>::from_slice(v)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl From<&str> for Rc<str> {
|
||
#[inline]
|
||
fn from(v: &str) -> Rc<str> {
|
||
let rc = Rc::<[u8]>::from(v.as_bytes());
|
||
unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl From<String> for Rc<str> {
|
||
#[inline]
|
||
fn from(v: String) -> Rc<str> {
|
||
Rc::from(&v[..])
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<T: ?Sized> From<Box<T>> for Rc<T> {
|
||
#[inline]
|
||
fn from(v: Box<T>) -> Rc<T> {
|
||
Rc::from_box(v)
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_slice", since = "1.21.0")]
|
||
impl<T> From<Vec<T>> for Rc<[T]> {
|
||
#[inline]
|
||
fn from(mut v: Vec<T>) -> Rc<[T]> {
|
||
unsafe {
|
||
let rc = Rc::copy_from_slice(&v);
|
||
|
||
// Allow the Vec to free its memory, but not destroy its contents
|
||
v.set_len(0);
|
||
|
||
rc
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_cow", since = "1.45.0")]
|
||
impl<'a, B> From<Cow<'a, B>> for Rc<B>
|
||
where
|
||
B: ToOwned + ?Sized,
|
||
Rc<B>: From<&'a B> + From<B::Owned>,
|
||
{
|
||
#[inline]
|
||
fn from(cow: Cow<'a, B>) -> Rc<B> {
|
||
match cow {
|
||
Cow::Borrowed(s) => Rc::from(s),
|
||
Cow::Owned(s) => Rc::from(s),
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "boxed_slice_try_from", since = "1.43.0")]
|
||
impl<T, const N: usize> TryFrom<Rc<[T]>> for Rc<[T; N]> {
|
||
type Error = Rc<[T]>;
|
||
|
||
fn try_from(boxed_slice: Rc<[T]>) -> Result<Self, Self::Error> {
|
||
if boxed_slice.len() == N {
|
||
Ok(unsafe { Rc::from_raw(Rc::into_raw(boxed_slice) as *mut [T; N]) })
|
||
} else {
|
||
Err(boxed_slice)
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "shared_from_iter", since = "1.37.0")]
|
||
impl<T> iter::FromIterator<T> for Rc<[T]> {
|
||
/// Takes each element in the `Iterator` and collects it into an `Rc<[T]>`.
|
||
///
|
||
/// # Performance characteristics
|
||
///
|
||
/// ## The general case
|
||
///
|
||
/// In the general case, collecting into `Rc<[T]>` is done by first
|
||
/// collecting into a `Vec<T>`. That is, when writing the following:
|
||
///
|
||
/// ```rust
|
||
/// # use std::rc::Rc;
|
||
/// let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();
|
||
/// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]);
|
||
/// ```
|
||
///
|
||
/// this behaves as if we wrote:
|
||
///
|
||
/// ```rust
|
||
/// # use std::rc::Rc;
|
||
/// let evens: Rc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
|
||
/// .collect::<Vec<_>>() // The first set of allocations happens here.
|
||
/// .into(); // A second allocation for `Rc<[T]>` happens here.
|
||
/// # assert_eq!(&*evens, &[0, 2, 4, 6, 8]);
|
||
/// ```
|
||
///
|
||
/// This will allocate as many times as needed for constructing the `Vec<T>`
|
||
/// and then it will allocate once for turning the `Vec<T>` into the `Rc<[T]>`.
|
||
///
|
||
/// ## Iterators of known length
|
||
///
|
||
/// When your `Iterator` implements `TrustedLen` and is of an exact size,
|
||
/// a single allocation will be made for the `Rc<[T]>`. For example:
|
||
///
|
||
/// ```rust
|
||
/// # use std::rc::Rc;
|
||
/// let evens: Rc<[u8]> = (0..10).collect(); // Just a single allocation happens here.
|
||
/// # assert_eq!(&*evens, &*(0..10).collect::<Vec<_>>());
|
||
/// ```
|
||
fn from_iter<I: iter::IntoIterator<Item = T>>(iter: I) -> Self {
|
||
ToRcSlice::to_rc_slice(iter.into_iter())
|
||
}
|
||
}
|
||
|
||
/// Specialization trait used for collecting into `Rc<[T]>`.
|
||
trait ToRcSlice<T>: Iterator<Item = T> + Sized {
|
||
fn to_rc_slice(self) -> Rc<[T]>;
|
||
}
|
||
|
||
impl<T, I: Iterator<Item = T>> ToRcSlice<T> for I {
|
||
default fn to_rc_slice(self) -> Rc<[T]> {
|
||
self.collect::<Vec<T>>().into()
|
||
}
|
||
}
|
||
|
||
impl<T, I: iter::TrustedLen<Item = T>> ToRcSlice<T> for I {
|
||
fn to_rc_slice(self) -> Rc<[T]> {
|
||
// This is the case for a `TrustedLen` iterator.
|
||
let (low, high) = self.size_hint();
|
||
if let Some(high) = high {
|
||
debug_assert_eq!(
|
||
low,
|
||
high,
|
||
"TrustedLen iterator's size hint is not exact: {:?}",
|
||
(low, high)
|
||
);
|
||
|
||
unsafe {
|
||
// SAFETY: We need to ensure that the iterator has an exact length and we have.
|
||
Rc::from_iter_exact(self, low)
|
||
}
|
||
} else {
|
||
// Fall back to normal implementation.
|
||
self.collect::<Vec<T>>().into()
|
||
}
|
||
}
|
||
}
|
||
|
||
/// `Weak` is a version of [`Rc`] that holds a non-owning reference to the
|
||
/// managed allocation. The allocation is accessed by calling [`upgrade`] on the `Weak`
|
||
/// pointer, which returns an [`Option`]`<`[`Rc`]`<T>>`.
|
||
///
|
||
/// Since a `Weak` reference does not count towards ownership, it will not
|
||
/// prevent the value stored in the allocation from being dropped, and `Weak` itself makes no
|
||
/// guarantees about the value still being present. Thus it may return [`None`]
|
||
/// when [`upgrade`]d. Note however that a `Weak` reference *does* prevent the allocation
|
||
/// itself (the backing store) from being deallocated.
|
||
///
|
||
/// A `Weak` pointer is useful for keeping a temporary reference to the allocation
|
||
/// managed by [`Rc`] without preventing its inner value from being dropped. It is also used to
|
||
/// prevent circular references between [`Rc`] pointers, since mutual owning references
|
||
/// would never allow either [`Rc`] to be dropped. For example, a tree could
|
||
/// have strong [`Rc`] pointers from parent nodes to children, and `Weak`
|
||
/// pointers from children back to their parents.
|
||
///
|
||
/// The typical way to obtain a `Weak` pointer is to call [`Rc::downgrade`].
|
||
///
|
||
/// [`upgrade`]: Weak::upgrade
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub struct Weak<T: ?Sized> {
|
||
// This is a `NonNull` to allow optimizing the size of this type in enums,
|
||
// but it is not necessarily a valid pointer.
|
||
// `Weak::new` sets this to `usize::MAX` so that it doesn’t need
|
||
// to allocate space on the heap. That's not a value a real pointer
|
||
// will ever have because RcBox has alignment at least 2.
|
||
// This is only possible when `T: Sized`; unsized `T` never dangle.
|
||
ptr: NonNull<RcBox<T>>,
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> !marker::Send for Weak<T> {}
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> !marker::Sync for Weak<T> {}
|
||
|
||
#[unstable(feature = "coerce_unsized", issue = "27732")]
|
||
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Weak<U>> for Weak<T> {}
|
||
|
||
#[unstable(feature = "dispatch_from_dyn", issue = "none")]
|
||
impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
|
||
|
||
impl<T> Weak<T> {
|
||
/// Constructs a new `Weak<T>`, without allocating any memory.
|
||
/// Calling [`upgrade`] on the return value always gives [`None`].
|
||
///
|
||
/// [`upgrade`]: Weak::upgrade
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Weak;
|
||
///
|
||
/// let empty: Weak<i64> = Weak::new();
|
||
/// assert!(empty.upgrade().is_none());
|
||
/// ```
|
||
#[stable(feature = "downgraded_weak", since = "1.10.0")]
|
||
pub fn new() -> Weak<T> {
|
||
Weak { ptr: NonNull::new(usize::MAX as *mut RcBox<T>).expect("MAX is not 0") }
|
||
}
|
||
|
||
/// Returns a raw pointer to the object `T` pointed to by this `Weak<T>`.
|
||
///
|
||
/// The pointer is valid only if there are some strong references. The pointer may be dangling,
|
||
/// unaligned or even [`null`] otherwise.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
/// use std::ptr;
|
||
///
|
||
/// let strong = Rc::new("hello".to_owned());
|
||
/// let weak = Rc::downgrade(&strong);
|
||
/// // Both point to the same object
|
||
/// assert!(ptr::eq(&*strong, weak.as_ptr()));
|
||
/// // The strong here keeps it alive, so we can still access the object.
|
||
/// assert_eq!("hello", unsafe { &*weak.as_ptr() });
|
||
///
|
||
/// drop(strong);
|
||
/// // But not any more. We can do weak.as_ptr(), but accessing the pointer would lead to
|
||
/// // undefined behaviour.
|
||
/// // assert_eq!("hello", unsafe { &*weak.as_ptr() });
|
||
/// ```
|
||
///
|
||
/// [`null`]: core::ptr::null
|
||
#[stable(feature = "rc_as_ptr", since = "1.45.0")]
|
||
pub fn as_ptr(&self) -> *const T {
|
||
let ptr: *mut RcBox<T> = NonNull::as_ptr(self.ptr);
|
||
|
||
// SAFETY: we must offset the pointer manually, and said pointer may be
|
||
// a dangling weak (usize::MAX) if T is sized. data_offset is safe to call,
|
||
// because we know that a pointer to unsized T was derived from a real
|
||
// unsized T, as dangling weaks are only created for sized T. wrapping_offset
|
||
// is used so that we can use the same code path for the non-dangling
|
||
// unsized case and the potentially dangling sized case.
|
||
unsafe {
|
||
let offset = data_offset(ptr as *mut T);
|
||
set_data_ptr(ptr as *mut T, (ptr as *mut u8).wrapping_offset(offset))
|
||
}
|
||
}
|
||
|
||
/// Consumes the `Weak<T>` and turns it into a raw pointer.
|
||
///
|
||
/// This converts the weak pointer into a raw pointer, while still preserving the ownership of
|
||
/// one weak reference (the weak count is not modified by this operation). It can be turned
|
||
/// back into the `Weak<T>` with [`from_raw`].
|
||
///
|
||
/// The same restrictions of accessing the target of the pointer as with
|
||
/// [`as_ptr`] apply.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// let strong = Rc::new("hello".to_owned());
|
||
/// let weak = Rc::downgrade(&strong);
|
||
/// let raw = weak.into_raw();
|
||
///
|
||
/// assert_eq!(1, Rc::weak_count(&strong));
|
||
/// assert_eq!("hello", unsafe { &*raw });
|
||
///
|
||
/// drop(unsafe { Weak::from_raw(raw) });
|
||
/// assert_eq!(0, Rc::weak_count(&strong));
|
||
/// ```
|
||
///
|
||
/// [`from_raw`]: Weak::from_raw
|
||
/// [`as_ptr`]: Weak::as_ptr
|
||
#[stable(feature = "weak_into_raw", since = "1.45.0")]
|
||
pub fn into_raw(self) -> *const T {
|
||
let result = self.as_ptr();
|
||
mem::forget(self);
|
||
result
|
||
}
|
||
|
||
/// Converts a raw pointer previously created by [`into_raw`] back into `Weak<T>`.
|
||
///
|
||
/// This can be used to safely get a strong reference (by calling [`upgrade`]
|
||
/// later) or to deallocate the weak count by dropping the `Weak<T>`.
|
||
///
|
||
/// It takes ownership of one weak reference (with the exception of pointers created by [`new`],
|
||
/// as these don't own anything; the method still works on them).
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// The pointer must have originated from the [`into_raw`] and must still own its potential
|
||
/// weak reference.
|
||
///
|
||
/// It is allowed for the strong count to be 0 at the time of calling this. Nevertheless, this
|
||
/// takes ownership of one weak reference currently represented as a raw pointer (the weak
|
||
/// count is not modified by this operation) and therefore it must be paired with a previous
|
||
/// call to [`into_raw`].
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// let strong = Rc::new("hello".to_owned());
|
||
///
|
||
/// let raw_1 = Rc::downgrade(&strong).into_raw();
|
||
/// let raw_2 = Rc::downgrade(&strong).into_raw();
|
||
///
|
||
/// assert_eq!(2, Rc::weak_count(&strong));
|
||
///
|
||
/// assert_eq!("hello", &*unsafe { Weak::from_raw(raw_1) }.upgrade().unwrap());
|
||
/// assert_eq!(1, Rc::weak_count(&strong));
|
||
///
|
||
/// drop(strong);
|
||
///
|
||
/// // Decrement the last weak count.
|
||
/// assert!(unsafe { Weak::from_raw(raw_2) }.upgrade().is_none());
|
||
/// ```
|
||
///
|
||
/// [`into_raw`]: Weak::into_raw
|
||
/// [`upgrade`]: Weak::upgrade
|
||
/// [`new`]: Weak::new
|
||
#[stable(feature = "weak_into_raw", since = "1.45.0")]
|
||
pub unsafe fn from_raw(ptr: *const T) -> Self {
|
||
if ptr.is_null() {
|
||
Self::new()
|
||
} else {
|
||
// See Rc::from_raw for details
|
||
unsafe {
|
||
let offset = data_offset(ptr);
|
||
let fake_ptr = ptr as *mut RcBox<T>;
|
||
let ptr = set_data_ptr(fake_ptr, (ptr as *mut u8).offset(-offset));
|
||
Weak { ptr: NonNull::new(ptr).expect("Invalid pointer passed to from_raw") }
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
pub(crate) fn is_dangling<T: ?Sized>(ptr: NonNull<T>) -> bool {
|
||
let address = ptr.as_ptr() as *mut () as usize;
|
||
address == usize::MAX
|
||
}
|
||
|
||
/// Helper type to allow accessing the reference counts without
|
||
/// making any assertions about the data field.
|
||
struct WeakInner<'a> {
|
||
weak: &'a Cell<usize>,
|
||
strong: &'a Cell<usize>,
|
||
}
|
||
|
||
impl<T: ?Sized> Weak<T> {
|
||
/// Attempts to upgrade the `Weak` pointer to an [`Rc`], delaying
|
||
/// dropping of the inner value if successful.
|
||
///
|
||
/// Returns [`None`] if the inner value has since been dropped.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let five = Rc::new(5);
|
||
///
|
||
/// let weak_five = Rc::downgrade(&five);
|
||
///
|
||
/// let strong_five: Option<Rc<_>> = weak_five.upgrade();
|
||
/// assert!(strong_five.is_some());
|
||
///
|
||
/// // Destroy all strong pointers.
|
||
/// drop(strong_five);
|
||
/// drop(five);
|
||
///
|
||
/// assert!(weak_five.upgrade().is_none());
|
||
/// ```
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
pub fn upgrade(&self) -> Option<Rc<T>> {
|
||
let inner = self.inner()?;
|
||
if inner.strong() == 0 {
|
||
None
|
||
} else {
|
||
inner.inc_strong();
|
||
Some(Rc::from_inner(self.ptr))
|
||
}
|
||
}
|
||
|
||
/// Gets the number of strong (`Rc`) pointers pointing to this allocation.
|
||
///
|
||
/// If `self` was created using [`Weak::new`], this will return 0.
|
||
#[stable(feature = "weak_counts", since = "1.41.0")]
|
||
pub fn strong_count(&self) -> usize {
|
||
if let Some(inner) = self.inner() { inner.strong() } else { 0 }
|
||
}
|
||
|
||
/// Gets the number of `Weak` pointers pointing to this allocation.
|
||
///
|
||
/// If no strong pointers remain, this will return zero.
|
||
#[stable(feature = "weak_counts", since = "1.41.0")]
|
||
pub fn weak_count(&self) -> usize {
|
||
self.inner()
|
||
.map(|inner| {
|
||
if inner.strong() > 0 {
|
||
inner.weak() - 1 // subtract the implicit weak ptr
|
||
} else {
|
||
0
|
||
}
|
||
})
|
||
.unwrap_or(0)
|
||
}
|
||
|
||
/// Returns `None` when the pointer is dangling and there is no allocated `RcBox`,
|
||
/// (i.e., when this `Weak` was created by `Weak::new`).
|
||
#[inline]
|
||
fn inner(&self) -> Option<WeakInner<'_>> {
|
||
if is_dangling(self.ptr) {
|
||
None
|
||
} else {
|
||
// We are careful to *not* create a reference covering the "data" field, as
|
||
// the field may be mutated concurrently (for example, if the last `Rc`
|
||
// is dropped, the data field will be dropped in-place).
|
||
Some(unsafe {
|
||
let ptr = self.ptr.as_ptr();
|
||
WeakInner { strong: &(*ptr).strong, weak: &(*ptr).weak }
|
||
})
|
||
}
|
||
}
|
||
|
||
/// Returns `true` if the two `Weak`s point to the same allocation (similar to
|
||
/// [`ptr::eq`]), or if both don't point to any allocation
|
||
/// (because they were created with `Weak::new()`).
|
||
///
|
||
/// # Notes
|
||
///
|
||
/// Since this compares pointers it means that `Weak::new()` will equal each
|
||
/// other, even though they don't point to any allocation.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Rc;
|
||
///
|
||
/// let first_rc = Rc::new(5);
|
||
/// let first = Rc::downgrade(&first_rc);
|
||
/// let second = Rc::downgrade(&first_rc);
|
||
///
|
||
/// assert!(first.ptr_eq(&second));
|
||
///
|
||
/// let third_rc = Rc::new(5);
|
||
/// let third = Rc::downgrade(&third_rc);
|
||
///
|
||
/// assert!(!first.ptr_eq(&third));
|
||
/// ```
|
||
///
|
||
/// Comparing `Weak::new`.
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// let first = Weak::new();
|
||
/// let second = Weak::new();
|
||
/// assert!(first.ptr_eq(&second));
|
||
///
|
||
/// let third_rc = Rc::new(());
|
||
/// let third = Rc::downgrade(&third_rc);
|
||
/// assert!(!first.ptr_eq(&third));
|
||
/// ```
|
||
///
|
||
/// [`ptr::eq`]: core::ptr::eq
|
||
#[inline]
|
||
#[stable(feature = "weak_ptr_eq", since = "1.39.0")]
|
||
pub fn ptr_eq(&self, other: &Self) -> bool {
|
||
self.ptr.as_ptr() == other.ptr.as_ptr()
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> Drop for Weak<T> {
|
||
/// Drops the `Weak` pointer.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// struct Foo;
|
||
///
|
||
/// impl Drop for Foo {
|
||
/// fn drop(&mut self) {
|
||
/// println!("dropped!");
|
||
/// }
|
||
/// }
|
||
///
|
||
/// let foo = Rc::new(Foo);
|
||
/// let weak_foo = Rc::downgrade(&foo);
|
||
/// let other_weak_foo = Weak::clone(&weak_foo);
|
||
///
|
||
/// drop(weak_foo); // Doesn't print anything
|
||
/// drop(foo); // Prints "dropped!"
|
||
///
|
||
/// assert!(other_weak_foo.upgrade().is_none());
|
||
/// ```
|
||
fn drop(&mut self) {
|
||
let inner = if let Some(inner) = self.inner() { inner } else { return };
|
||
|
||
inner.dec_weak();
|
||
// the weak count starts at 1, and will only go to zero if all
|
||
// the strong pointers have disappeared.
|
||
if inner.weak() == 0 {
|
||
unsafe {
|
||
Global.dealloc(self.ptr.cast(), Layout::for_value(self.ptr.as_ref()));
|
||
}
|
||
}
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized> Clone for Weak<T> {
|
||
/// Makes a clone of the `Weak` pointer that points to the same allocation.
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::{Rc, Weak};
|
||
///
|
||
/// let weak_five = Rc::downgrade(&Rc::new(5));
|
||
///
|
||
/// let _ = Weak::clone(&weak_five);
|
||
/// ```
|
||
#[inline]
|
||
fn clone(&self) -> Weak<T> {
|
||
if let Some(inner) = self.inner() {
|
||
inner.inc_weak()
|
||
}
|
||
Weak { ptr: self.ptr }
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rc_weak", since = "1.4.0")]
|
||
impl<T: ?Sized + fmt::Debug> fmt::Debug for Weak<T> {
|
||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
||
write!(f, "(Weak)")
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "downgraded_weak", since = "1.10.0")]
|
||
impl<T> Default for Weak<T> {
|
||
/// Constructs a new `Weak<T>`, allocating memory for `T` without initializing
|
||
/// it. Calling [`upgrade`] on the return value always gives [`None`].
|
||
///
|
||
/// [`None`]: Option
|
||
/// [`upgrade`]: Weak::upgrade
|
||
///
|
||
/// # Examples
|
||
///
|
||
/// ```
|
||
/// use std::rc::Weak;
|
||
///
|
||
/// let empty: Weak<i64> = Default::default();
|
||
/// assert!(empty.upgrade().is_none());
|
||
/// ```
|
||
fn default() -> Weak<T> {
|
||
Weak::new()
|
||
}
|
||
}
|
||
|
||
// NOTE: We checked_add here to deal with mem::forget safely. In particular
|
||
// if you mem::forget Rcs (or Weaks), the ref-count can overflow, and then
|
||
// you can free the allocation while outstanding Rcs (or Weaks) exist.
|
||
// We abort because this is such a degenerate scenario that we don't care about
|
||
// what happens -- no real program should ever experience this.
|
||
//
|
||
// This should have negligible overhead since you don't actually need to
|
||
// clone these much in Rust thanks to ownership and move-semantics.
|
||
|
||
#[doc(hidden)]
|
||
trait RcInnerPtr {
|
||
fn weak_ref(&self) -> &Cell<usize>;
|
||
fn strong_ref(&self) -> &Cell<usize>;
|
||
|
||
#[inline]
|
||
fn strong(&self) -> usize {
|
||
self.strong_ref().get()
|
||
}
|
||
|
||
#[inline]
|
||
fn inc_strong(&self) {
|
||
let strong = self.strong();
|
||
|
||
// We want to abort on overflow instead of dropping the value.
|
||
// The reference count will never be zero when this is called;
|
||
// nevertheless, we insert an abort here to hint LLVM at
|
||
// an otherwise missed optimization.
|
||
if strong == 0 || strong == usize::MAX {
|
||
abort();
|
||
}
|
||
self.strong_ref().set(strong + 1);
|
||
}
|
||
|
||
#[inline]
|
||
fn dec_strong(&self) {
|
||
self.strong_ref().set(self.strong() - 1);
|
||
}
|
||
|
||
#[inline]
|
||
fn weak(&self) -> usize {
|
||
self.weak_ref().get()
|
||
}
|
||
|
||
#[inline]
|
||
fn inc_weak(&self) {
|
||
let weak = self.weak();
|
||
|
||
// We want to abort on overflow instead of dropping the value.
|
||
// The reference count will never be zero when this is called;
|
||
// nevertheless, we insert an abort here to hint LLVM at
|
||
// an otherwise missed optimization.
|
||
if weak == 0 || weak == usize::MAX {
|
||
abort();
|
||
}
|
||
self.weak_ref().set(weak + 1);
|
||
}
|
||
|
||
#[inline]
|
||
fn dec_weak(&self) {
|
||
self.weak_ref().set(self.weak() - 1);
|
||
}
|
||
}
|
||
|
||
impl<T: ?Sized> RcInnerPtr for RcBox<T> {
|
||
#[inline(always)]
|
||
fn weak_ref(&self) -> &Cell<usize> {
|
||
&self.weak
|
||
}
|
||
|
||
#[inline(always)]
|
||
fn strong_ref(&self) -> &Cell<usize> {
|
||
&self.strong
|
||
}
|
||
}
|
||
|
||
impl<'a> RcInnerPtr for WeakInner<'a> {
|
||
#[inline(always)]
|
||
fn weak_ref(&self) -> &Cell<usize> {
|
||
self.weak
|
||
}
|
||
|
||
#[inline(always)]
|
||
fn strong_ref(&self) -> &Cell<usize> {
|
||
self.strong
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "rust1", since = "1.0.0")]
|
||
impl<T: ?Sized> borrow::Borrow<T> for Rc<T> {
|
||
fn borrow(&self) -> &T {
|
||
&**self
|
||
}
|
||
}
|
||
|
||
#[stable(since = "1.5.0", feature = "smart_ptr_as_ref")]
|
||
impl<T: ?Sized> AsRef<T> for Rc<T> {
|
||
fn as_ref(&self) -> &T {
|
||
&**self
|
||
}
|
||
}
|
||
|
||
#[stable(feature = "pin", since = "1.33.0")]
|
||
impl<T: ?Sized> Unpin for Rc<T> {}
|
||
|
||
/// Get the offset within an `RcBox` for
|
||
/// a payload of type described by a pointer.
|
||
///
|
||
/// # Safety
|
||
///
|
||
/// This has the same safety requirements as `align_of_val_raw`. In effect:
|
||
///
|
||
/// - This function is safe for any argument if `T` is sized, and
|
||
/// - if `T` is unsized, the pointer must have appropriate pointer metadata
|
||
/// acquired from the real instance that you are getting this offset for.
|
||
unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> isize {
|
||
// Align the unsized value to the end of the `RcBox`.
|
||
// Because it is ?Sized, it will always be the last field in memory.
|
||
// Note: This is a detail of the current implementation of the compiler,
|
||
// and is not a guaranteed language detail. Do not rely on it outside of std.
|
||
unsafe { data_offset_align(align_of_val_raw(ptr)) }
|
||
}
|
||
|
||
#[inline]
|
||
fn data_offset_align(align: usize) -> isize {
|
||
let layout = Layout::new::<RcBox<()>>();
|
||
(layout.size() + layout.padding_needed_for(align)) as isize
|
||
}
|