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rkjnsn/rc.rs

Created April 27, 2015 21:00
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Initial attempt and implementing scoped RcGuard to clean up cycles.
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rc.rs
// Copyright 2013-2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.
//! Thread-local reference-counted boxes (the `Rc<T>` type).
//!
//! The `Rc<T>` type provides shared ownership of an immutable value.
//! Destruction is deterministic, and will occur as soon as the last owner is
//! gone. It is marked as non-sendable because it avoids the overhead of atomic
//! reference counting.
//!
//! The `downgrade` method can be used to create a non-owning `Weak<T>` pointer
//! to the box. A `Weak<T>` pointer can be upgraded to an `Rc<T>` pointer, but
//! will return `None` if the value has already been dropped.
//!
//! For example, a tree with parent pointers can be represented by putting the
//! nodes behind strong `Rc<T>` pointers, and then storing the parent pointers
//! as `Weak<T>` pointers.
//!
//! # Examples
//!
//! Consider a scenario where a set of `Gadget`s are owned by a given `Owner`.
//! We want to have our `Gadget`s point to their `Owner`. We can't do this with
//! unique ownership, because more than one gadget may belong to the same
//! `Owner`. `Rc<T>` allows us to share an `Owner` between multiple `Gadget`s,
//! and have the `Owner` remain allocated as long as any `Gadget` points at it.
//!
//! ```rust
//! # #![feature(alloc, collections)]
//! use std::rc::Rc;
//!
//! struct Owner {
//! name: String
//! // ...other fields
//! }
//!
//! struct Gadget {
//! id: i32,
//! owner: Rc<Owner>
//! // ...other fields
//! }
//!
//! fn main() {
//! // Create a reference counted Owner.
//! let gadget_owner : Rc<Owner> = Rc::new(
//! Owner { name: String::from_str("Gadget Man") }
//! );
//!
//! // Create Gadgets belonging to gadget_owner. To increment the reference
//! // count we clone the `Rc<T>` object.
//! let gadget1 = Gadget { id: 1, owner: gadget_owner.clone() };
//! let gadget2 = Gadget { id: 2, owner: gadget_owner.clone() };
//!
//! drop(gadget_owner);
//!
//! // Despite dropping gadget_owner, we're still able to print out the name
//! // of the Owner of the Gadgets. This is because we've only dropped the
//! // reference count object, not the Owner it wraps. As long as there are
//! // other `Rc<T>` objects pointing at the same Owner, it will remain
//! // allocated. Notice that the `Rc<T>` wrapper around Gadget.owner gets
//! // automatically dereferenced for us.
//! println!("Gadget {} owned by {}", gadget1.id, gadget1.owner.name);
//! println!("Gadget {} owned by {}", gadget2.id, gadget2.owner.name);
//!
//! // At the end of the method, gadget1 and gadget2 get destroyed, and with
//! // them the last counted references to our Owner. Gadget Man now gets
//! // destroyed as well.
//! }
//! ```
//!
//! If our requirements change, and we also need to be able to traverse from
//! Owner → Gadget, we will run into problems: an `Rc<T>` pointer from Owner
//! → Gadget introduces a cycle between the objects. This means that their
//! reference counts can never reach 0, and the objects will remain allocated: a
//! memory leak. In order to get around this, we can use `Weak<T>` pointers.
//! These pointers don't contribute to the total count.
//!
//! Rust actually makes it somewhat difficult to produce this loop in the first
//! place: in order to end up with two objects that point at each other, one of
//! them needs to be mutable. This is problematic because `Rc<T>` enforces
//! memory safety by only giving out shared references to the object it wraps,
//! and these don't allow direct mutation. We need to wrap the part of the
//! object we wish to mutate in a `RefCell`, which provides *interior
//! mutability*: a method to achieve mutability through a shared reference.
//! `RefCell` enforces Rust's borrowing rules at runtime. Read the `Cell`
//! documentation for more details on interior mutability.
//!
//! ```rust
//! # #![feature(alloc)]
//! use std::rc::Rc;
//! use std::rc::Weak;
//! use std::cell::RefCell;
//!
//! struct Owner {
//! name: String,
//! gadgets: RefCell<Vec<Weak<Gadget>>>
//! // ...other fields
//! }
//!
//! struct Gadget {
//! id: i32,
//! owner: Rc<Owner>
//! // ...other fields
//! }
//!
//! fn main() {
//! // Create a reference counted Owner. Note the fact that we've put the
//! // Owner's vector of Gadgets inside a RefCell so that we can mutate it
//! // through a shared reference.
//! let gadget_owner : Rc<Owner> = Rc::new(
//! Owner {
//! name: "Gadget Man".to_string(),
//! gadgets: RefCell::new(Vec::new())
//! }
//! );
//!
//! // Create Gadgets belonging to gadget_owner as before.
//! let gadget1 = Rc::new(Gadget{id: 1, owner: gadget_owner.clone()});
//! let gadget2 = Rc::new(Gadget{id: 2, owner: gadget_owner.clone()});
//!
//! // Add the Gadgets to their Owner. To do this we mutably borrow from
//! // the RefCell holding the Owner's Gadgets.
//! gadget_owner.gadgets.borrow_mut().push(gadget1.clone().downgrade());
//! gadget_owner.gadgets.borrow_mut().push(gadget2.clone().downgrade());
//!
//! // Iterate over our Gadgets, printing their details out
//! for gadget_opt in gadget_owner.gadgets.borrow().iter() {
//!
//! // gadget_opt is a Weak<Gadget>. Since weak pointers can't guarantee
//! // that their object is still allocated, we need to call upgrade()
//! // on them to turn them into a strong reference. This returns an
//! // Option, which contains a reference to our object if it still
//! // exists.
//! let gadget = gadget_opt.upgrade().unwrap();
//! println!("Gadget {} owned by {}", gadget.id, gadget.owner.name);
//! }
//!
//! // At the end of the method, gadget_owner, gadget1 and gadget2 get
//! // destroyed. There are now no strong (`Rc<T>`) references to the gadgets.
//! // Once they get destroyed, the Gadgets get destroyed. This zeroes the
//! // reference count on Gadget Man, so he gets destroyed as well.
//! }
//! ```
#![stable(feature = "rust1", since = "1.0.0")]
#[cfg(not(test))]
use boxed;
#[cfg(test)]
use std::boxed;
use core::cell::{Cell, UnsafeCell};
use core::clone::Clone;
use core::cmp::{PartialEq, PartialOrd, Eq, Ord, Ordering, max};
use core::default::Default;
use core::fmt;
use core::hash::{Hasher, Hash};
use core::marker;
use core::mem::{self, min_align_of, size_of, forget};
use core::nonzero::NonZero;
use core::ops::{Deref, Drop};
use core::option::Option;
use core::option::Option::{Some, None};
use core::ptr;
use core::raw::TraitObject;
use core::result::Result;
use core::result::Result::{Ok, Err};
use core::intrinsics::{assume, transmute};
use core::isize;
use heap::{EMPTY, allocate, deallocate, reallocate};
struct RcBox<T> {
value: T,
strong: Cell<usize>,
weak: Cell<usize>
}
/// A reference-counted pointer type over an immutable value.
///
/// See the [module level documentation](./index.html) for more details.
#[unsafe_no_drop_flag]
#[stable(feature = "rust1", since = "1.0.0")]
pub struct Rc<T> {
// FIXME #12808: strange names to try to avoid interfering with field
// accesses of the contained type via Deref
_ptr: NonZero<*mut RcBox<T>>,
}
impl<T> !marker::Send for Rc<T> {}
impl<T> !marker::Sync for Rc<T> {}
impl<T> Rc<T> {
/// Constructs a new `Rc<T>`.
///
/// `value` is not guaranteed to be dropped if it is part of a cycle, and
/// so must be valid for the `'static` lifetime.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
/// ```
#[stable(feature = "rust1", since = "1.0.0")]
pub fn new(value: T) -> Rc<T> where T: 'static {
unsafe {
Rc::unsafe_new(value)
}
}
/// Constructs a new `Rc<T>` of any lifetime.
///
/// Allows creating an `Rc` containing a `value` that has a lifetime
/// shorter than `'static`. Care must be taken to ensure that the contained
/// value is destroyed by the end of its lifetime (e.g., by avoiding
/// cycles).
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = 5;
/// let five_ref = Rc::unsafe_new(&five);
/// ```
#[unstable(feature = "alloc",
reason = "May be better to have a separate UnsafeRc type")]
pub unsafe fn unsafe_new(value: T) -> Rc<T> {
Rc {
// there is an implicit weak pointer owned by all the strong
// pointers, which ensures that the weak destructor never frees
// the allocation while the strong destructor is running, even
// if the weak pointer is stored inside the strong one.
_ptr: NonZero::new(boxed::into_raw(box RcBox {
value: value,
strong: Cell::new(1),
weak: Cell::new(1)
})),
}
}
/// Downgrades the `Rc<T>` to a `Weak<T>` reference.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// let weak_five = five.downgrade();
/// ```
#[unstable(feature = "alloc",
reason = "Weak pointers may not belong in this module")]
pub fn downgrade(&self) -> Weak<T> {
self.inc_weak();
Weak { _ptr: self._ptr }
}
}
/// Get the number of weak references to this value.
#[inline]
#[unstable(feature = "alloc")]
pub fn weak_count<T>(this: &Rc<T>) -> usize { this.weak() - 1 }
/// Get the number of strong references to this value.
#[inline]
#[unstable(feature = "alloc")]
pub fn strong_count<T>(this: &Rc<T>) -> usize { this.strong() }
/// Returns true if there are no other `Rc` or `Weak<T>` values that share the
/// same inner value.
///
/// Note that RcGuard works by holding a weak reference, so this will always be
/// false for guarded Rc's.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc;
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// rc::is_unique(&five);
/// ```
#[inline]
#[unstable(feature = "alloc")]
pub fn is_unique<T>(rc: &Rc<T>) -> bool {
weak_count(rc) == 0 && strong_count(rc) == 1
}
/// Unwraps the contained value if the `Rc<T>` is the only strong reference.
///
/// Unlike get_mut, this works whenever `strong_count` is one, even if there
/// are weak references, and thus works for guarded Rc's. If the `Rc<T>` is not
/// unique, an `Err` is returned with the same `Rc<T>`.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::{self, Rc};
///
/// let x = Rc::new(3);
/// assert_eq!(rc::try_unwrap(x), Ok(3));
///
/// let x = Rc::new(4);
/// let _y = x.clone();
/// assert_eq!(rc::try_unwrap(x), Err(Rc::new(4)));
/// ```
#[inline]
#[unstable(feature = "alloc")]
pub fn try_unwrap<T>(rc: Rc<T>) -> Result<T, Rc<T>> {
if strong_count(&rc) == 1 {
unsafe {
rc.dec_strong();
// We know strong count is now 0
let val = ptr::read(&rc.inner().value); // copy the contained object
// remove the implicit "strong weak" pointer now that we've
// removed the contents.
rc.dec_weak();
if rc.weak() == 0 {
deallocate(*rc._ptr as *mut u8, size_of::<RcBox<T>>(),
min_align_of::<RcBox<T>>());
}
// Skip our Drop
forget(rc);
Ok(val)
}
} else {
Err(rc)
}
}
/// Unwraps the contained value if the `Rc<T>` is the only strong reference. If
/// not, the value is cloned.
#[inline]
#[unstable(feature = "alloc")]
pub fn unwrap_or_clone<T: Clone>(rc: Rc<T>) -> T {
if strong_count(&rc) == 1 {
unsafe {
rc.dec_strong();
// We know strong count is now 0
let val = ptr::read(&rc.inner().value); // copy the contained object
// remove the implicit "strong weak" pointer now that we've
// removed the contents.
rc.dec_weak();
if rc.weak() == 0 {
deallocate(*rc._ptr as *mut u8, size_of::<RcBox<T>>(),
min_align_of::<RcBox<T>>());
}
// Skip our Drop
forget(rc);
val
}
} else {
(*rc).clone()
}
}
/// Returns a mutable reference to the contained value if the `Rc<T>` is unique.
///
/// Returns `None` if the `Rc<T>` is not unique. Note that RcGuard works by
/// holding a weak pointer, so this will always None for a Guarded Rc.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::{self, Rc};
///
/// let mut x = Rc::new(3);
/// *rc::get_mut(&mut x).unwrap() = 4;
/// assert_eq!(*x, 4);
///
/// let _y = x.clone();
/// assert!(rc::get_mut(&mut x).is_none());
/// ```
#[inline]
#[unstable(feature = "alloc")]
pub fn get_mut<T>(rc: &mut Rc<T>) -> Option<&mut T> {
if is_unique(rc) {
let inner = unsafe { &mut **rc._ptr };
Some(&mut inner.value)
} else {
None
}
}
impl<T: Clone> Rc<T> {
/// Make a mutable reference from the given `Rc<T>`.
///
/// This is also referred to as a copy-on-write operation because the inner
/// data is cloned if the reference count is greater than one.
///
/// Note that the result will not be guarded, even if self is.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let mut five = Rc::new(5);
///
/// let mut_five = five.unsafe_make_unique();
/// ```
#[inline]
#[unstable(feature = "alloc")]
pub unsafe fn unsafe_make_unique(&mut self) -> &mut T {
if !is_unique(self) {
*self = Rc::unsafe_new((**self).clone())
}
// 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 inner value.
let inner = &mut **self._ptr;
&mut inner.value
}
}
impl<T: 'static+Clone> Rc<T> {
/// Make a mutable reference from the given `Rc<T>`.
///
/// This is also referred to as a copy-on-write operation because the inner
/// data is cloned if the reference count is greater than one.
///
/// Note that the result will not be guarded, even if self is.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let mut five = Rc::new(5);
///
/// let mut_five = five.make_unique();
/// ```
#[inline]
#[unstable(feature = "alloc")]
pub fn make_unique(&mut self) -> &mut T {
// Safe because T: 'static
unsafe { self.unsafe_make_unique() }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Deref for Rc<T> {
type Target = T;
#[inline(always)]
fn deref(&self) -> &T {
if self.strong() == 0 {
panic!("Rc deferenced after guard was dropped");
}
&self.inner().value
}
}
#[unsafe_destructor]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Drop for Rc<T> {
/// Drops the `Rc<T>`.
///
/// This will decrement the strong reference count. If the strong reference
/// count becomes zero and the only other references are `Weak<T>` ones,
/// `drop`s the inner value.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// {
/// let five = Rc::new(5);
///
/// // stuff
///
/// drop(five); // explicit drop
/// }
/// {
/// let five = Rc::new(5);
///
/// // stuff
///
/// } // implicit drop
/// ```
fn drop(&mut self) {
unsafe {
let ptr = *self._ptr;
if !ptr.is_null() && ptr as usize != mem::POST_DROP_USIZE {
if self.strong() != 0 {
self.dec_strong();
if self.strong() == 0 {
// Can't use Deref with strong() == 0
ptr::read(&self.inner().value); // destroy the contained object
}
}
if self.strong() == 0 {
// We were either the last strong pointer or the guard has
// been destroyed. Either way, we need to decrement weak
self.dec_weak();
if self.weak() == 0 {
deallocate(ptr as *mut u8, size_of::<RcBox<T>>(),
min_align_of::<RcBox<T>>())
}
}
}
}
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Clone for Rc<T> {
/// Makes a clone of the `Rc<T>`.
///
/// When you clone an `Rc<T>`, it will create another pointer to the data and
/// increase the strong reference counter.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five.clone();
/// ```
#[inline]
fn clone(&self) -> Rc<T> {
if self.strong() != 0 {
self.inc_strong();
}
Rc { _ptr: self._ptr }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: 'static+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();
/// ```
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
fn default() -> Rc<T> {
Rc::new(Default::default())
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: PartialEq> PartialEq for Rc<T> {
/// Equality for two `Rc<T>`s.
///
/// Two `Rc<T>`s are equal if their inner value are equal.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five == Rc::new(5);
/// ```
#[inline(always)]
fn eq(&self, other: &Rc<T>) -> bool { **self == **other }
/// Inequality for two `Rc<T>`s.
///
/// Two `Rc<T>`s are unequal if their inner value are unequal.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five != Rc::new(5);
/// ```
#[inline(always)]
fn ne(&self, other: &Rc<T>) -> bool { **self != **other }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Eq> Eq for Rc<T> {}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: PartialOrd> PartialOrd for Rc<T> {
/// Partial comparison for two `Rc<T>`s.
///
/// The two are compared by calling `partial_cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five.partial_cmp(&Rc::new(5));
/// ```
#[inline(always)]
fn partial_cmp(&self, other: &Rc<T>) -> Option<Ordering> {
(**self).partial_cmp(&**other)
}
/// Less-than comparison for two `Rc<T>`s.
///
/// The two are compared by calling `<` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five < Rc::new(5);
/// ```
#[inline(always)]
fn lt(&self, other: &Rc<T>) -> bool { **self < **other }
/// 'Less-than or equal to' comparison for two `Rc<T>`s.
///
/// The two are compared by calling `<=` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five <= Rc::new(5);
/// ```
#[inline(always)]
fn le(&self, other: &Rc<T>) -> bool { **self <= **other }
/// Greater-than comparison for two `Rc<T>`s.
///
/// The two are compared by calling `>` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five > Rc::new(5);
/// ```
#[inline(always)]
fn gt(&self, other: &Rc<T>) -> bool { **self > **other }
/// 'Greater-than or equal to' comparison for two `Rc<T>`s.
///
/// The two are compared by calling `>=` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five >= Rc::new(5);
/// ```
#[inline(always)]
fn ge(&self, other: &Rc<T>) -> bool { **self >= **other }
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Ord> Ord for Rc<T> {
/// Comparison for two `Rc<T>`s.
///
/// The two are compared by calling `cmp()` on their inner values.
///
/// # Examples
///
/// ```
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// five.partial_cmp(&Rc::new(5));
/// ```
#[inline]
fn cmp(&self, other: &Rc<T>) -> Ordering { (**self).cmp(&**other) }
}
// FIXME (#18248) Make `T` `Sized?`
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: 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: 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: 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> fmt::Pointer for Rc<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
fmt::Pointer::fmt(&*self._ptr, f)
}
}
/// A weak version of `Rc<T>`.
///
/// Weak references do not count when determining if the inner value should be
/// dropped.
///
/// See the [module level documentation](./index.html) for more.
#[unsafe_no_drop_flag]
#[unstable(feature = "alloc",
reason = "Weak pointers may not belong in this module.")]
pub struct Weak<T> {
// FIXME #12808: strange names to try to avoid interfering with
// field accesses of the contained type via Deref
_ptr: NonZero<*mut RcBox<T>>,
}
impl<T> !marker::Send for Weak<T> {}
impl<T> !marker::Sync for Weak<T> {}
#[unstable(feature = "alloc",
reason = "Weak pointers may not belong in this module.")]
impl<T> Weak<T> {
/// Upgrades a weak reference to a strong reference.
///
/// Upgrades the `Weak<T>` reference to an `Rc<T>`, if possible.
///
/// Returns `None` if there were no strong references and the data was
/// destroyed.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let five = Rc::new(5);
///
/// let weak_five = five.downgrade();
///
/// let strong_five: Option<Rc<_>> = weak_five.upgrade();
/// ```
pub fn upgrade(&self) -> Option<Rc<T>> {
if self.strong() == 0 {
None
} else {
self.inc_strong();
Some(Rc { _ptr: self._ptr })
}
}
}
#[unsafe_destructor]
#[stable(feature = "rust1", since = "1.0.0")]
impl<T> Drop for Weak<T> {
/// Drops the `Weak<T>`.
///
/// This will decrement the weak reference count.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// {
/// let five = Rc::new(5);
/// let weak_five = five.downgrade();
///
/// // stuff
///
/// drop(weak_five); // explicit drop
/// }
/// {
/// let five = Rc::new(5);
/// let weak_five = five.downgrade();
///
/// // stuff
///
/// } // implicit drop
/// ```
fn drop(&mut self) {
unsafe {
let ptr = *self._ptr;
if !ptr.is_null() && ptr as usize != mem::POST_DROP_USIZE {
self.dec_weak();
// the weak count starts at 1, and will only go to zero if all
// the strong pointers have disappeared.
if self.weak() == 0 {
deallocate(ptr as *mut u8, size_of::<RcBox<T>>(),
min_align_of::<RcBox<T>>())
}
}
}
}
}
#[unstable(feature = "alloc",
reason = "Weak pointers may not belong in this module.")]
impl<T> Clone for Weak<T> {
/// Makes a clone of the `Weak<T>`.
///
/// This increases the weak reference count.
///
/// # Examples
///
/// ```
/// # #![feature(alloc)]
/// use std::rc::Rc;
///
/// let weak_five = Rc::new(5).downgrade();
///
/// weak_five.clone();
/// ```
#[inline]
fn clone(&self) -> Weak<T> {
self.inc_weak();
Weak { _ptr: self._ptr }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: fmt::Debug> fmt::Debug for Weak<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
write!(f, "(Weak)")
}
}
#[doc(hidden)]
trait RcBoxPtr<T> {
fn inner(&self) -> &RcBox<T>;
#[inline]
fn strong(&self) -> usize { self.inner().strong.get() }
#[inline]
fn inc_strong(&self) { self.inner().strong.set(self.strong() + 1); }
#[inline]
fn dec_strong(&self) { self.inner().strong.set(self.strong() - 1); }
#[inline]
fn weak(&self) -> usize { self.inner().weak.get() }
#[inline]
fn inc_weak(&self) { self.inner().weak.set(self.weak() + 1); }
#[inline]
fn dec_weak(&self) { self.inner().weak.set(self.weak() - 1); }
}
impl<T> RcBoxPtr<T> for Rc<T> {
#[inline(always)]
fn inner(&self) -> &RcBox<T> {
unsafe {
// Safe to assume this here, as if it weren't true, we'd be breaking
// the contract anyway.
// This allows the null check to be elided in the destructor if we
// manipulated the reference count in the same function.
assume(!self._ptr.is_null());
&(**self._ptr)
}
}
}
impl<T> RcBoxPtr<T> for Weak<T> {
#[inline(always)]
fn inner(&self) -> &RcBox<T> {
unsafe {
// Safe to assume this here, as if it weren't true, we'd be breaking
// the contract anyway.
// This allows the null check to be elided in the destructor if we
// manipulated the reference count in the same function.
assume(!self._ptr.is_null());
&(**self._ptr)
}
}
}
// Operation the guard can perform on held weak references. Make this a trait
// so the compiler will make a vtable for us.
trait GuardOps {
// Moves the strong count to the weak count. All strong references will
// effectively become weak references.
fn force_drop(&self);
// Release our internally held weak reference.
fn release_weak(&self);
// Determine whether the object is alive (still has strong refs)
fn is_alive(&self) -> bool;
}
// We want this Copy for safety when forcefully dropping objects so include raw
// pointer instead of a Weak<T>
struct GuardRef<T> {
rc_box: NonZero<*mut RcBox<T>>,
}
impl<T> GuardRef<T> {
fn new(ptr: NonZero<*mut RcBox<T>>) -> GuardRef<T> {
GuardRef { rc_box: ptr }
}
}
impl<T> RcBoxPtr<T> for GuardRef<T> {
#[inline(always)]
fn inner(&self) -> &RcBox<T> {
unsafe {
// Safe to assume this here, as if it weren't true, we'd be breaking
// the contract anyway.
// This allows the null check to be elided in the destructor if we
// manipulated the reference count in the same function.
assume(!self.rc_box.is_null());
&(**self.rc_box)
}
}
}
impl<T> GuardOps for GuardRef<T> {
fn force_drop(&self) {
if self.strong() != 0 {
// Make all strong references weak. (Minus 1 to relase the "strong weak")
self.inner().weak.set(self.inner().weak.get() + self.inner().strong.get() - 1);
self.inner().strong.set(0);
// Drop the contained value
unsafe {ptr::read(&self.inner().value)};
}
}
fn release_weak(&self) {
unsafe {
self.dec_weak();
if self.weak() == 0 {
deallocate(*self.rc_box as *mut u8, size_of::<RcBox<T>>(),
min_align_of::<RcBox<T>>());
}
}
}
fn is_alive(&self) -> bool {
self.strong() != 0
}
}
impl<T> marker::Copy for GuardRef<T> {}
impl<T> Clone for GuardRef<T> {
fn clone(&self) -> GuardRef<T> {
*self
}
}
// Type erases a GuardRef (through very hacky means)
struct DynamicGuardRef {
guard_ref: GuardRef<()>, // All GuardRefs are the same size
vtable: * mut (), // The compiler-generated GuardOps vtable for guard_ref
}
impl DynamicGuardRef {
fn new<T>(guard_ref: GuardRef<T>) -> DynamicGuardRef {
unsafe {
let vtable = {
let ops_obj: &GuardOps = &guard_ref;
let trait_obj: TraitObject = transmute(ops_obj);
trait_obj.vtable
};
DynamicGuardRef {
guard_ref: transmute(guard_ref),
vtable: vtable,
}
}
}
}
impl marker::Copy for DynamicGuardRef {}
impl Clone for DynamicGuardRef {
fn clone(&self) -> DynamicGuardRef {
*self
}
}
impl Deref for DynamicGuardRef {
type Target = GuardOps;
// For some reason, just -> &GuardOps doesn't work (bug?)
fn deref(&self) -> &<DynamicGuardRef as Deref>::Target {
unsafe {
let guard_ref_ptr: *const GuardRef<()> = &self.guard_ref;
transmute(TraitObject {data: guard_ref_ptr as *mut (), vtable: self.vtable})
}
}
}
struct GuardRefVec {
// We're basically reimplementing a subset of Vec here.
ptr: ptr::Unique<DynamicGuardRef>,
len: usize,
cap: usize,
}
const MAX_MEMORY_SIZE: usize = isize::MAX as usize;
impl GuardRefVec {
fn new() -> GuardRefVec {
// We want ptr to never be NULL so instead we set it to some arbitrary
// non-null value which is fine since we never call deallocate on the ptr
// if cap is 0. The reason for this is because the pointer of a slice
// being NULL would break the null pointer optimization for enums.
unsafe {
GuardRefVec {
ptr: ptr::Unique::new(EMPTY as *mut DynamicGuardRef),
len: 0,
cap: 0,
}
}
}
fn push(&mut self, value: DynamicGuardRef) {
#[cold]
#[inline(never)]
fn resize(vec: &mut GuardRefVec) {
let old_size = vec.cap * mem::size_of::<DynamicGuardRef>();
if old_size >= MAX_MEMORY_SIZE { panic!("capacity overflow") }
let mut size = max(old_size, 2 * mem::size_of::<DynamicGuardRef>()) * 2;
if old_size > size || size > MAX_MEMORY_SIZE {
size = MAX_MEMORY_SIZE;
}
unsafe {
let ptr = if old_size == 0 {
allocate(size, mem::min_align_of::<DynamicGuardRef>()) as *mut DynamicGuardRef
} else {
reallocate(*vec.ptr as *mut u8, old_size, size,
mem::min_align_of::<DynamicGuardRef>()) as *mut DynamicGuardRef
};
if ptr.is_null() { ::oom() }
vec.ptr = ptr::Unique::new(ptr);
}
vec.cap = max(vec.cap, 2) * 2;
}
if self.len == self.cap {
resize(self);
}
unsafe {
let end = (*self.ptr).offset(self.len as isize);
ptr::write(&mut *end, value);
self.len += 1;
}
}
fn len(&self) -> usize { self.len }
// We don't want to use an iterator because the list could potentially grow
// while we're iterating in some cases. DynamicGuardRef is Copy, so it will
// stay valid even if we are reallocated while it's in use.
unsafe fn get_unchecked(&self, index: usize) -> DynamicGuardRef {
*self.ptr.offset(index as isize)
}
unsafe fn set_unchecked(&mut self, index: usize, val: DynamicGuardRef) {
*self.ptr.offset(index as isize) = val;
}
unsafe fn set_len(&mut self, len: usize) { self.len = len; }
}
impl Drop for GuardRefVec {
fn drop(&mut self) {
if self.cap != 0 {
unsafe {
// We're not running any destructors, now, so fetching the length
// once should be safe
for i in 0..self.len {
self.get_unchecked(i).release_weak();
}
deallocate(*self.ptr as *mut u8, self.cap * mem::size_of::<DynamicGuardRef>(),
mem::min_align_of::<DynamicGuardRef>());
}
}
}
}
/// A guard to ensure that all associated Rc objects, including cycles, are
/// cleaned up it goes out of scope.
///
/// `RcGuard` works by effectively turning all associated strong references
/// into weak references. Any attempt to dereference an `Rc` whose associated
/// `RcGuard` has been dropped will result in a panic. Be especially careful
/// in the destructor of any object that may be part of an `Rc` cycle, as any
/// contained `Rc`s may have already been reclaimed. Use `check_valid` to
/// determine if the value is still alive and act accordingly.
#[unstable(feature = "alloc", reason = "RcGuard is experimental.")]
pub struct RcGuard<'a> {
// We need to be able to add to the list even though we'll be borrowed by
// previously returned Rc's.
guard_refs: UnsafeCell<GuardRefVec>,
scope: marker::PhantomData<Cell<&'a ()>>, // 'a is invariant
}
impl<'a> RcGuard<'a> {
/// Create a new `RcGuard`
pub fn new() -> RcGuard<'a> {
RcGuard {
guard_refs: UnsafeCell::new(GuardRefVec::new()),
scope: marker::PhantomData,
}
}
/// Create a new `Rc` guarded by this `RcGuard`
pub fn new_rc<T: 'a>(&self, val: T) -> Rc<T> {
// val is guaranteed to be valid for the lifetime of this guard, so
// including it in an associated Rc is safe.
unsafe {
// In addition to the implicit "strong weak" pointer, we hold a
// weak pointer to allow us to clean up cycles.
let ptr = NonZero::new(boxed::into_raw(box RcBox {
value: val,
strong: Cell::new(1),
weak: Cell::new(2)
}));
// Used to clean-up cycles.
(*self.guard_refs.get()).push(DynamicGuardRef::new(GuardRef::new(ptr)));
Rc { _ptr: ptr }
}
}
/// Drop the weak ref for any guarded `Rc`s with no remaining strong refs
/// to reclaim space
pub fn purge_dropped(&self) {
// We aren't running any external code, so it's safe to cache this
let vec = unsafe { &mut *self.guard_refs.get() };
let len = vec.len();
let mut read_pos = 0;
let mut write_pos = 0;
unsafe {
while read_pos < len {
let guard_ref = vec.get_unchecked(read_pos);
if guard_ref.is_alive() {
vec.set_unchecked(write_pos, guard_ref);
write_pos += 1;
} else {
guard_ref.release_weak();
}
read_pos += 1;
}
vec.set_len(write_pos);
}
}
}
// Clean up any remaining cycles
#[unsafe_destructor]
impl<'a> Drop for RcGuard<'a> {
fn drop(&mut self) {
unsafe {
// One of the reference-counted objects could pathologically hold a
// reference to us and create new cycles in it's destructor, so
// always index and check against the current length
let mut i = 0;
while i < (*self.guard_refs.get()).len() {
(*self.guard_refs.get()).get_unchecked(i).force_drop();
i += 1;
}
}
}
}
/// Checks that the given Rc is still valid.
///
/// `Rc`s become invalid when the associated guard (if any) goes out of scope.
/// Use this to check for validity in the destructors of potential cycles or
/// anywhere an `Rc` could potentially outlive its `RcGuard`.
#[unstable(feature = "alloc", reason = "RcGuard is experimental.")]
pub fn check_valid<T>(rc: Rc<T>) -> Option<Rc<T>> {
if rc.strong() != 0 {
Some(rc)
} else {
None
}
}
#[cfg(test)]
mod tests {
use super::{Rc, Weak, weak_count, strong_count};
use std::boxed::Box;
use std::cell::RefCell;
use std::option::Option;
use std::option::Option::{Some, None};
use std::result::Result::{Err, Ok};
use std::mem::drop;
use std::clone::Clone;
#[test]
fn test_clone() {
let x = Rc::new(RefCell::new(5));
let y = x.clone();
*x.borrow_mut() = 20;
assert_eq!(*y.borrow(), 20);
}
#[test]
fn test_simple() {
let x = Rc::new(5);
assert_eq!(*x, 5);
}
#[test]
fn test_simple_clone() {
let x = Rc::new(5);
let y = x.clone();
assert_eq!(*x, 5);
assert_eq!(*y, 5);
}
#[test]
fn test_destructor() {
let x: Rc<Box<_>> = Rc::new(box 5);
assert_eq!(**x, 5);
}
#[test]
fn test_live() {
let x = Rc::new(5);
let y = x.downgrade();
assert!(y.upgrade().is_some());
}
#[test]
fn test_dead() {
let x = Rc::new(5);
let y = x.downgrade();
drop(x);
assert!(y.upgrade().is_none());
}
#[test]
fn weak_self_cyclic() {
struct Cycle {
x: RefCell<Option<Weak<Cycle>>>
}
let a = Rc::new(Cycle { x: RefCell::new(None) });
let b = a.clone().downgrade();
*a.x.borrow_mut() = Some(b);
// hopefully we don't double-free (or leak)...
}
#[test]
fn is_unique() {
let x = Rc::new(3);
assert!(super::is_unique(&x));
let y = x.clone();
assert!(!super::is_unique(&x));
drop(y);
assert!(super::is_unique(&x));
let w = x.downgrade();
assert!(!super::is_unique(&x));
drop(w);
assert!(super::is_unique(&x));
}
#[test]
fn test_strong_count() {
let a = Rc::new(0u32);
assert!(strong_count(&a) == 1);
let w = a.downgrade();
assert!(strong_count(&a) == 1);
let b = w.upgrade().expect("upgrade of live rc failed");
assert!(strong_count(&b) == 2);
assert!(strong_count(&a) == 2);
drop(w);
drop(a);
assert!(strong_count(&b) == 1);
let c = b.clone();
assert!(strong_count(&b) == 2);
assert!(strong_count(&c) == 2);
}
#[test]
fn test_weak_count() {
let a = Rc::new(0u32);
assert!(strong_count(&a) == 1);
assert!(weak_count(&a) == 0);
let w = a.downgrade();
assert!(strong_count(&a) == 1);
assert!(weak_count(&a) == 1);
drop(w);
assert!(strong_count(&a) == 1);
assert!(weak_count(&a) == 0);
let c = a.clone();
assert!(strong_count(&a) == 2);
assert!(weak_count(&a) == 0);
drop(c);
}
#[test]
fn try_unwrap() {
let x = Rc::new(3);
assert_eq!(super::try_unwrap(x), Ok(3));
let x = Rc::new(4);
let _y = x.clone();
assert_eq!(super::try_unwrap(x), Err(Rc::new(4)));
let x = Rc::new(5);
let _w = x.downgrade();
assert_eq!(super::try_unwrap(x), Err(Rc::new(5)));
}
#[test]
fn get_mut() {
let mut x = Rc::new(3);
*super::get_mut(&mut x).unwrap() = 4;
assert_eq!(*x, 4);
let y = x.clone();
assert!(super::get_mut(&mut x).is_none());
drop(y);
assert!(super::get_mut(&mut x).is_some());
let _w = x.downgrade();
assert!(super::get_mut(&mut x).is_none());
}
#[test]
fn test_cowrc_clone_make_unique() {
let mut cow0 = Rc::new(75);
let mut cow1 = cow0.clone();
let mut cow2 = cow1.clone();
assert!(75 == *cow0.make_unique());
assert!(75 == *cow1.make_unique());
assert!(75 == *cow2.make_unique());
*cow0.make_unique() += 1;
*cow1.make_unique() += 2;
*cow2.make_unique() += 3;
assert!(76 == *cow0);
assert!(77 == *cow1);
assert!(78 == *cow2);
// none should point to the same backing memory
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 != *cow2);
}
#[test]
fn test_cowrc_clone_unique2() {
let mut cow0 = Rc::new(75);
let cow1 = cow0.clone();
let cow2 = cow1.clone();
assert!(75 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
*cow0.make_unique() += 1;
assert!(76 == *cow0);
assert!(75 == *cow1);
assert!(75 == *cow2);
// cow1 and cow2 should share the same contents
// cow0 should have a unique reference
assert!(*cow0 != *cow1);
assert!(*cow0 != *cow2);
assert!(*cow1 == *cow2);
}
#[test]
fn test_cowrc_clone_weak() {
let mut cow0 = Rc::new(75);
let cow1_weak = cow0.downgrade();
assert!(75 == *cow0);
assert!(75 == *cow1_weak.upgrade().unwrap());
*cow0.make_unique() += 1;
assert!(76 == *cow0);
assert!(cow1_weak.upgrade().is_none());
}
#[test]
fn test_show() {
let foo = Rc::new(75);
assert_eq!(format!("{:?}", foo), "75");
}
}
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