1.4.0[−][src]Struct std::sync::Weak
Weak is a version of Arc that holds a non-owning reference to the
managed value. The value is accessed by calling upgrade on the Weak
pointer, which returns an Option<Arc<T>>.
Since a Weak reference does not count towards ownership, it will not
prevent the inner value from being dropped, and Weak itself makes no
guarantees about the value still being present and may return None
when upgraded.
A Weak pointer is useful for keeping a temporary reference to the value
within Arc without extending its lifetime. It is also used to prevent
circular references between Arc pointers, since mutual owning references
would never allow either Arc to be dropped. For example, a tree could
have strong Arc 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 Arc::downgrade.
Methods
impl<T> Weak<T>[src]
impl<T> Weak<T> where
T: ?Sized, [src]
T: ?Sized,
pub fn upgrade(&self) -> Option<Arc<T>>[src]
Attempts to upgrade the Weak pointer to an Arc, extending
the lifetime of the value if successful.
Returns None if the value has since been dropped.
Examples
use std::sync::Arc; let five = Arc::new(5); let weak_five = Arc::downgrade(&five); let strong_five: Option<Arc<_>> = weak_five.upgrade(); assert!(strong_five.is_some()); // Destroy all strong pointers. drop(strong_five); drop(five); assert!(weak_five.upgrade().is_none());Run
pub fn strong_count(&self) -> usize[src]
Gets the number of strong (Arc) pointers pointing to this value.
If self was created using Weak::new, this will return 0.
pub fn weak_count(&self) -> Option<usize>[src]
Gets an approximation of the number of Weak pointers pointing to this
value.
If self was created using Weak::new, this will return 0. If not,
the returned value is at least 1, since self still points to the
value.
Accuracy
Due to implementation details, the returned value can be off by 1 in
either direction when other threads are manipulating any Arcs or
Weaks pointing to the same value.
pub fn ptr_eq(this: &Weak<T>, other: &Weak<T>) -> bool[src]
Returns true if the two Weaks point to the same value (not just values
that compare as equal).
Notes
Since this compares pointers it means that Weak::new() will equal each
other, even though they don't point to any value.
Examples
#![feature(weak_ptr_eq)] use std::sync::{Arc, Weak}; let first_rc = Arc::new(5); let first = Arc::downgrade(&first_rc); let second = Arc::downgrade(&first_rc); assert!(Weak::ptr_eq(&first, &second)); let third_rc = Arc::new(5); let third = Arc::downgrade(&third_rc); assert!(!Weak::ptr_eq(&first, &third));Run
Comparing Weak::new.
#![feature(weak_ptr_eq)] use std::sync::{Arc, Weak}; let first = Weak::new(); let second = Weak::new(); assert!(Weak::ptr_eq(&first, &second)); let third_rc = Arc::new(()); let third = Arc::downgrade(&third_rc); assert!(!Weak::ptr_eq(&first, &third));Run
Trait Implementations
impl<T> Default for Weak<T>1.10.0[src]
impl<T> Sync for Weak<T> where
T: Send + Sync + ?Sized, [src]
T: Send + Sync + ?Sized,
impl<T> Send for Weak<T> where
T: Send + Sync + ?Sized, [src]
T: Send + Sync + ?Sized,
impl<T, U> CoerceUnsized<Weak<U>> for Weak<T> where
T: Unsize<U> + ?Sized,
U: ?Sized, [src]
T: Unsize<U> + ?Sized,
U: ?Sized,
impl<T> Debug for Weak<T> where
T: Debug + ?Sized, [src]
T: Debug + ?Sized,
impl<T> Drop for Weak<T> where
T: ?Sized, [src]
T: ?Sized,
fn drop(&mut self)[src]
Drops the Weak pointer.
Examples
use std::sync::{Arc, Weak}; struct Foo; impl Drop for Foo { fn drop(&mut self) { println!("dropped!"); } } let foo = Arc::new(Foo); let weak_foo = Arc::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());Run
impl<T, U> DispatchFromDyn<Weak<U>> for Weak<T> where
T: Unsize<U> + ?Sized,
U: ?Sized, [src]
T: Unsize<U> + ?Sized,
U: ?Sized,
impl<T> Clone for Weak<T> where
T: ?Sized, [src]
T: ?Sized,
fn clone(&self) -> Weak<T>[src]
Makes a clone of the Weak pointer that points to the same value.
Examples
use std::sync::{Arc, Weak}; let weak_five = Arc::downgrade(&Arc::new(5)); let _ = Weak::clone(&weak_five);Run
fn clone_from(&mut self, source: &Self)1.0.0[src]
Performs copy-assignment from source. Read more
Blanket Implementations
impl<T, U> TryFrom for T where
U: Into<T>, [src]
U: Into<T>,
type Error = Infallible
The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>[src]
impl<T> From for T[src]
impl<T, U> TryInto for T where
U: TryFrom<T>, [src]
U: TryFrom<T>,
type Error = <U as TryFrom<T>>::Error
The type returned in the event of a conversion error.
fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>[src]
impl<T, U> Into for T where
U: From<T>, [src]
U: From<T>,
impl<T> Borrow for T where
T: ?Sized, [src]
T: ?Sized,
impl<T> BorrowMut for T where
T: ?Sized, [src]
T: ?Sized,
ⓘImportant traits for &'_ mut Ifn borrow_mut(&mut self) -> &mut T[src]
impl<T> Any for T where
T: 'static + ?Sized, [src]
T: 'static + ?Sized,
impl<T> ToOwned for T where
T: Clone, [src]
T: Clone,