# Struct std::sync::Arc 1.0.0 [−] [src]

    pub struct Arc<T> where T: ?Sized {
        // some fields omitted
    }

An atomically reference counted wrapper for shared state. 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.

# Examples

In this example, a large vector of data will be shared by several threads. First we wrap it with a `Arc::new` and then clone the `Arc<T>` reference for every thread (which will increase the reference count atomically).

use std::sync::Arc; use std::thread; fn main() { let numbers: Vec<_> = (0..100).collect(); let shared_numbers = Arc::new(numbers); for _ in 0..10 { // prepare a copy of reference here and it will be moved to the thread let child_numbers = shared_numbers.clone(); thread::spawn(move || { let local_numbers = &child_numbers[..]; // Work with the local numbers }); } }

    use std::sync::Arc;
    use std::thread;

    fn main() {
        let numbers: Vec<_> = (0..100).collect();
        let shared_numbers = Arc::new(numbers);

        for _ in 0..10 {
            // prepare a copy of reference here and it will be moved to the thread
            let child_numbers = shared_numbers.clone();

            thread::spawn(move || {
                let local_numbers = &child_numbers[..];

                // Work with the local numbers
            });
        }
    }

You can also share mutable data between threads safely by putting it inside `Mutex` and then share `Mutex` immutably with `Arc<T>` as shown below.

fn main() { 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 }); } }

    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
        });
    }

## Methods

### `impl<T> Arc<T>`

#### `fn new(data: T) -> Arc<T>`

Constructs a new `Arc<T>`.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

#### `fn try_unwrap(this: Arc<T>) -> Result<T, Arc<T>>`
1.4.0

Unwraps the contained value if the `Arc<T>` has exactly one strong reference.

Otherwise, an `Err` is returned with the same `Arc<T>`.

This will succeed even if there are outstanding weak references.

# Examples

fn main() { use std::sync::Arc; let x = Arc::new(3); assert_eq!(Arc::try_unwrap(x), Ok(3)); let x = Arc::new(4); let _y = x.clone(); assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4))); }

    use std::sync::Arc;

    let x = Arc::new(3);
    assert_eq!(Arc::try_unwrap(x), Ok(3));

    let x = Arc::new(4);
    let _y = x.clone();
    assert_eq!(Arc::try_unwrap(x), Err(Arc::new(4)));

### `impl<T> Arc<T> where T: ?Sized`

#### `fn downgrade(this: &Arc<T>) -> Weak<T>`
1.4.0

Downgrades the `Arc<T>` to a `Weak<T>` reference.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); let weak_five = Arc::downgrade(&five); }

    use std::sync::Arc;

    let five = Arc::new(5);

    let weak_five = Arc::downgrade(&five);

#### `fn weak_count(this: &Arc<T>) -> usize`

Unstable (`arc_counts` #28356)

: not clearly useful, and racy

Get the number of weak references to this value.

#### `fn strong_count(this: &Arc<T>) -> usize`

Unstable (`arc_counts` #28356)

: not clearly useful, and racy

Get the number of strong references to this value.

### `impl<T> Arc<T> where T: Clone`

#### `fn make_mut(this: &mut Arc<T>) -> &mut T`
1.4.0

Make a mutable reference into the given `Arc<T>`. If the `Arc<T>` has more than one strong reference, or any weak references, the inner data is cloned.

This is also referred to as a copy-on-write.

# Examples

fn main() { use std::sync::Arc; let mut data = Arc::new(5); *Arc::make_mut(&mut data) += 1; // Won't clone anything let mut other_data = data.clone(); // Won't clone inner data *Arc::make_mut(&mut data) += 1; // Clones inner data *Arc::make_mut(&mut data) += 1; // Won't clone anything *Arc::make_mut(&mut other_data) *= 2; // Won't clone anything // Note: data and other_data now point to different numbers assert_eq!(*data, 8); assert_eq!(*other_data, 12); }

    use std::sync::Arc;

    let mut data = Arc::new(5);

    *Arc::make_mut(&mut data) += 1;         // Won't clone anything
    let mut other_data = data.clone();      // Won't clone inner data
    *Arc::make_mut(&mut data) += 1;         // Clones inner data
    *Arc::make_mut(&mut data) += 1;         // Won't clone anything
    *Arc::make_mut(&mut other_data) *= 2;   // Won't clone anything

    // Note: data and other_data now point to different numbers
    assert_eq!(*data, 8);
    assert_eq!(*other_data, 12);

### `impl<T> Arc<T> where T: ?Sized`

#### `fn get_mut(this: &mut Arc<T>) -> Option<&mut T>`
1.4.0

Returns a mutable reference to the contained value if the `Arc<T>` has one strong reference and no weak references.

# Examples

fn main() { use std::sync::Arc; let mut x = Arc::new(3); *Arc::get_mut(&mut x).unwrap() = 4; assert_eq!(*x, 4); let _y = x.clone(); assert!(Arc::get_mut(&mut x).is_none()); }

    use std::sync::Arc;

    let mut x = Arc::new(3);
    *Arc::get_mut(&mut x).unwrap() = 4;
    assert_eq!(*x, 4);

    let _y = x.clone();
    assert!(Arc::get_mut(&mut x).is_none());

## Trait Implementations

### `impl<T> Send for Arc<T> where T: Send + Sync + ?Sized`

### `impl<T> Sync for Arc<T> where T: Send + Sync + ?Sized`

### `impl<T, U> CoerceUnsized<Arc<U>> for Arc<T> where T: Unsize<U> + ?Sized, U: ?Sized`

### `impl<T> Clone for Arc<T> where T: ?Sized`

#### `fn clone(&self) -> Arc<T>`

Makes a clone of the `Arc<T>`.

This increases the strong reference count.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five.clone(); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five.clone();

#### `fn clone_from(&mut self, source: &Self)`

Performs copy-assignment from `source`. Read more

### `impl<T> Deref for Arc<T> where T: ?Sized`

#### `type Target = T`

The resulting type after dereferencing

#### `fn deref(&self) -> &T`

The method called to dereference a value

### `impl<T> Drop for Arc<T> where T: ?Sized`

#### `fn drop(&mut self)`

Drops the `Arc<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

fn main() { use std::sync::Arc; { let five = Arc::new(5); // stuff drop(five); // explicit drop } { let five = Arc::new(5); // stuff } // implicit drop }

    use std::sync::Arc;

    {
        let five = Arc::new(5);

        // stuff

        drop(five); // explicit drop
    }
    {
        let five = Arc::new(5);

        // stuff

    } // implicit drop

### `impl<T> PartialEq<Arc<T>> for Arc<T> where T: PartialEq<T> + ?Sized`

#### `fn eq(&self, other: &Arc<T>) -> bool`

Equality for two `Arc<T>`s.

Two `Arc<T>`s are equal if their inner value are equal.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five == Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five == Arc::new(5);

#### `fn ne(&self, other: &Arc<T>) -> bool`

Inequality for two `Arc<T>`s.

Two `Arc<T>`s are unequal if their inner value are unequal.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five != Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five != Arc::new(5);

### `impl<T> PartialOrd<Arc<T>> for Arc<T> where T: PartialOrd<T> + ?Sized`

#### `fn partial_cmp(&self, other: &Arc<T>) -> Option<Ordering>`

Partial comparison for two `Arc<T>`s.

The two are compared by calling `partial_cmp()` on their inner values.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five.partial_cmp(&Arc::new(5)); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five.partial_cmp(&Arc::new(5));

#### `fn lt(&self, other: &Arc<T>) -> bool`

Less-than comparison for two `Arc<T>`s.

The two are compared by calling `<` on their inner values.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five < Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five < Arc::new(5);

#### `fn le(&self, other: &Arc<T>) -> bool`

'Less-than or equal to' comparison for two `Arc<T>`s.

The two are compared by calling `<=` on their inner values.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five <= Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five <= Arc::new(5);

#### `fn gt(&self, other: &Arc<T>) -> bool`

Greater-than comparison for two `Arc<T>`s.

The two are compared by calling `>` on their inner values.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five > Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five > Arc::new(5);

#### `fn ge(&self, other: &Arc<T>) -> bool`

'Greater-than or equal to' comparison for two `Arc<T>`s.

The two are compared by calling `>=` on their inner values.

# Examples

fn main() { use std::sync::Arc; let five = Arc::new(5); five >= Arc::new(5); }

    use std::sync::Arc;

    let five = Arc::new(5);

    five >= Arc::new(5);

### `impl<T> Ord for Arc<T> where T: Ord + ?Sized`

#### `fn cmp(&self, other: &Arc<T>) -> Ordering`

This method returns an `Ordering` between `self` and `other`. Read more

### `impl<T> Eq for Arc<T> where T: Eq + ?Sized`

### `impl<T> Display for Arc<T> where T: Display + ?Sized`

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`

Formats the value using the given formatter.

### `impl<T> Debug for Arc<T> where T: Debug + ?Sized`

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`

Formats the value using the given formatter.

### `impl<T> Pointer for Arc<T> where T: ?Sized`

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`

Formats the value using the given formatter.

### `impl<T> Default for Arc<T> where T: Default`

#### `fn default() -> Arc<T>`

Returns the "default value" for a type. Read more

### `impl<T> Hash for Arc<T> where T: Hash + ?Sized`

#### `fn hash<H>(&self, state: &mut H) where H: Hasher`

Feeds this value into the state given, updating the hasher as necessary.

#### `fn hash_slice<H>(data: &[Self], state: &mut H) where H: Hasher`
1.3.0

Feeds a slice of this type into the state provided.

### `impl<T> From<T> for Arc<T>`
1.6.0

#### `fn from(t: T) -> Arc<T>`

Performs the conversion.

### `impl<T> Borrow<T> for Arc<T> where T: ?Sized`

#### `fn borrow(&self) -> &T`

Immutably borrows from an owned value. Read more

### `impl<T> AsRef<T> for Arc<T> where T: ?Sized`
1.5.0

#### `fn as_ref(&self) -> &T`

Performs the conversion.

### `impl<T: RefUnwindSafe + ?Sized> UnwindSafe for Arc<T>`
1.9.0
[src]

# Help

## Keyboard Shortcuts

?
  Show this help dialog
S
  Focus the search field
⇤
  Move up in search results
⇥
  Move down in search results
⏎
  Go to active search result
+
  Collapse/expand all sections

## Search Tricks

Prefix searches with a type followed by a colon (e.g. `fn:`) to restrict the search to a given type.

Accepted types are: `fn`, `mod`, `struct`, `enum`, `trait`, `type`, `macro`, and `const`.

Search functions by type signature (e.g. `vec -> usize` or `* -> vec`)