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rc.rs
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rc.rs
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// Copyright 2013 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.
/*! Task-local reference-counted boxes (`Rc` type)
The `Rc` 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` pointer to the box. A `Weak`
pointer can be upgraded to an `Rc` pointer, but will return `None` if the value has already been
freed.
For example, a tree with parent pointers can be represented by putting the nodes behind `Strong`
pointers, and then storing the parent pointers as `Weak` pointers.
*/
use cast::transmute;
use ops::Drop;
use cmp::{Eq, Ord};
use clone::{Clone, DeepClone};
use rt::global_heap::exchange_free;
use ptr::read_ptr;
use option::{Option, Some, None};
struct RcBox<T> {
value: T,
strong: uint,
weak: uint
}
/// Immutable reference counted pointer type
#[unsafe_no_drop_flag]
#[no_send]
pub struct Rc<T> {
priv ptr: *mut RcBox<T>
}
impl<T> Rc<T> {
/// Construct a new reference-counted box
pub fn new(value: T) -> Rc<T> {
unsafe {
Rc { ptr: transmute(~RcBox { value: value, strong: 1, weak: 0 }) }
}
}
}
impl<T> Rc<T> {
/// Borrow the value contained in the reference-counted box
#[inline(always)]
pub fn borrow<'a>(&'a self) -> &'a T {
unsafe { &(*self.ptr).value }
}
/// Downgrade the reference-counted pointer to a weak reference
pub fn downgrade(&self) -> Weak<T> {
unsafe {
(*self.ptr).weak += 1;
Weak { ptr: self.ptr }
}
}
}
#[unsafe_destructor]
impl<T> Drop for Rc<T> {
fn drop(&mut self) {
unsafe {
if self.ptr != 0 as *mut RcBox<T> {
(*self.ptr).strong -= 1;
if (*self.ptr).strong == 0 {
read_ptr(self.borrow()); // destroy the contained object
if (*self.ptr).weak == 0 {
exchange_free(self.ptr as *u8)
}
}
}
}
}
}
impl<T> Clone for Rc<T> {
#[inline]
fn clone(&self) -> Rc<T> {
unsafe {
(*self.ptr).strong += 1;
Rc { ptr: self.ptr }
}
}
}
impl<T: DeepClone> DeepClone for Rc<T> {
#[inline]
fn deep_clone(&self) -> Rc<T> {
Rc::new(self.borrow().deep_clone())
}
}
impl<T: Eq> Eq for Rc<T> {
#[inline(always)]
fn eq(&self, other: &Rc<T>) -> bool { *self.borrow() == *other.borrow() }
#[inline(always)]
fn ne(&self, other: &Rc<T>) -> bool { *self.borrow() != *other.borrow() }
}
impl<T: Ord> Ord for Rc<T> {
#[inline(always)]
fn lt(&self, other: &Rc<T>) -> bool { *self.borrow() < *other.borrow() }
#[inline(always)]
fn le(&self, other: &Rc<T>) -> bool { *self.borrow() <= *other.borrow() }
#[inline(always)]
fn gt(&self, other: &Rc<T>) -> bool { *self.borrow() > *other.borrow() }
#[inline(always)]
fn ge(&self, other: &Rc<T>) -> bool { *self.borrow() >= *other.borrow() }
}
/// Weak reference to a reference-counted box
#[unsafe_no_drop_flag]
#[no_send]
pub struct Weak<T> {
priv ptr: *mut RcBox<T>
}
impl<T> Weak<T> {
/// Upgrade a weak reference to a strong reference
pub fn upgrade(&self) -> Option<Rc<T>> {
unsafe {
if (*self.ptr).strong == 0 {
None
} else {
(*self.ptr).strong += 1;
Some(Rc { ptr: self.ptr })
}
}
}
}
#[unsafe_destructor]
impl<T> Drop for Weak<T> {
fn drop(&mut self) {
unsafe {
if self.ptr != 0 as *mut RcBox<T> {
(*self.ptr).weak -= 1;
if (*self.ptr).weak == 0 && (*self.ptr).strong == 0 {
exchange_free(self.ptr as *u8)
}
}
}
}
}
impl<T> Clone for Weak<T> {
#[inline]
fn clone(&self) -> Weak<T> {
unsafe {
(*self.ptr).weak += 1;
Weak { ptr: self.ptr }
}
}
}
#[cfg(test)]
mod tests {
use prelude::*;
use super::*;
use cell::RefCell;
#[test]
fn test_clone() {
let x = Rc::new(RefCell::new(5));
let y = x.clone();
x.borrow().with_mut(|inner| {
*inner = 20;
});
assert_eq!(y.borrow().with(|v| *v), 20);
}
#[test]
fn test_deep_clone() {
let x = Rc::new(RefCell::new(5));
let y = x.deep_clone();
x.borrow().with_mut(|inner| {
*inner = 20;
});
assert_eq!(y.borrow().with(|v| *v), 5);
}
#[test]
fn test_simple() {
let x = Rc::new(5);
assert_eq!(*x.borrow(), 5);
}
#[test]
fn test_simple_clone() {
let x = Rc::new(5);
let y = x.clone();
assert_eq!(*x.borrow(), 5);
assert_eq!(*y.borrow(), 5);
}
#[test]
fn test_destructor() {
let x = Rc::new(~5);
assert_eq!(**x.borrow(), 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 gc_inside() {
// see issue #11532
use gc::Gc;
let a = Rc::new(RefCell::new(Gc::new(1)));
assert!(a.borrow().try_borrow_mut().is_some());
}
}