Module alloc::arc
[−]
[src]
Threadsafe reference-counted boxes (the Arc<T>
type).
The Arc<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 Send
because it uses atomic reference counting.
If you do not need thread-safety, and just need shared ownership, consider
the Rc<T>
type. It is the same as Arc<T>
, but
does not use atomics, making it both thread-unsafe as well as significantly
faster when updating the reference count.
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 Arc<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 Arc<T>
pointers, and then storing the parent pointers
as Weak<T>
pointers.
Examples
Sharing some immutable data between threads:
use std::sync::Arc; use std::thread; let five = Arc::new(5); for _ in 0..10 { let five = five.clone(); thread::spawn(move || { println!("{:?}", five); }); }
Sharing mutable data safely between threads with a Mutex
:
use std::sync::{Arc, Mutex}; use std::thread; let five = Arc::new(Mutex::new(5)); for _ in 0..10 { let five = five.clone(); thread::spawn(move || { let mut number = five.lock().unwrap(); *number += 1; println!("{}", *number); // prints 6 }); }
Reexports
use core::prelude::v1::*; |
use boxed::Box; |
use core::sync::atomic; |
use core::sync::atomic::Ordering::{Relaxed, Release, Acquire, SeqCst}; |
use core::borrow; |
use core::fmt; |
use core::cmp::Ordering; |
use core::mem::{align_of_val, size_of_val}; |
use core::intrinsics::abort; |
use core::mem; |
use core::mem::uninitialized; |
use core::ops::Deref; |
use core::ops::CoerceUnsized; |
use core::ptr::{self, Shared}; |
use core::marker::Unsize; |
use core::hash::{Hash, Hasher}; |
use core::{usize, isize}; |
use core::convert::From; |
use heap::deallocate; |
Structs
Arc |
An atomically reference counted wrapper for shared state. |
ArcInner | |
Weak |
A weak pointer to an |
Constants
MAX_REFCOUNT |