Struct Arc

pub struct Arc<T>
where
    T: ?Sized,
{ /* private fields */ }

A thread-safe reference-counting pointer. ‘Arc’ stands for ‘Atomically Reference Counted’.

This is an equivalent to [std::sync::Arc], but using portable-atomic for synchronization. See the documentation for [std::sync::Arc] for more details.

Note: Unlike std::sync::Arc, coercing Arc<T> to Arc<U> is only possible if the optional cfg portable_atomic_unstable_coerce_unsized is enabled, as documented at the crate-level documentation, and this optional cfg item is only supported with Rust nightly version. This is because coercing the pointee requires the unstable CoerceUnsized trait. See this issue comment for a workaround that works without depending on unstable features.

Examples

use portable_atomic_util::Arc;
use std::thread;

let five = Arc::new(5);

for _ in 0..10 {
    let five = Arc::clone(&five);

    thread::spawn(move || {
        assert_eq!(*five, 5);
    });
}

Implementations

impl<T> Arc<T>

pub fn new(data: T) -> Arc<T>

Constructs a new Arc<T>.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

pub fn new_cyclic<F>(data_fn: F) -> Arc<T>

where F: FnOnce(&Weak<T>) -> T,

Constructs a new Arc<T> while giving you a Weak<T> to the allocation, to allow you to construct a T which holds a weak pointer to itself.

Generally, a structure circularly referencing itself, either directly or indirectly, should not hold a strong reference to itself to prevent a memory leak. Using this function, you get access to the weak pointer during the initialization of T, before the Arc<T> is created, such that you can clone and store it inside the T.

new_cyclic first allocates the managed allocation for the Arc<T>, then calls your closure, giving it a Weak<T> to this allocation, and only afterwards completes the construction of the Arc<T> by placing the T returned from your closure into the allocation.

Since the new Arc<T> is not fully-constructed until Arc<T>::new_cyclic returns, calling upgrade on the weak reference inside your closure will fail and result in a None value.

Panics

If data_fn panics, the panic is propagated to the caller, and the temporary Weak<T> is dropped normally.

Example

use portable_atomic_util::{Arc, Weak};

struct Gadget {
    me: Weak<Gadget>,
}

impl Gadget {
    /// Constructs a reference counted Gadget.
    fn new() -> Arc<Self> {
        // `me` is a `Weak<Gadget>` pointing at the new allocation of the
        // `Arc` we're constructing.
        Arc::new_cyclic(|me| {
            // Create the actual struct here.
            Gadget { me: me.clone() }
        })
    }

    /// Returns a reference counted pointer to Self.
    fn me(&self) -> Arc<Self> {
        self.me.upgrade().unwrap()
    }
}

pub fn new_uninit() -> Arc<MaybeUninit<T>>

Constructs a new Arc with uninitialized contents.

Examples

use portable_atomic_util::Arc;

let mut five = Arc::<u32>::new_uninit();

// Deferred initialization:
Arc::get_mut(&mut five).unwrap().write(5);

let five = unsafe { five.assume_init() };

assert_eq!(*five, 5)

pub fn pin(data: T) -> Pin<Arc<T>>

Constructs a new Pin<Arc<T>>. If T does not implement Unpin, then data will be pinned in memory and unable to be moved.

pub fn try_unwrap(this: Arc<T>) -> Result<T, Arc<T>>

Returns the inner value, if the Arc has exactly one strong reference.

Otherwise, an Err is returned with the same Arc that was passed in.

This will succeed even if there are outstanding weak references.

It is strongly recommended to use Arc::into_inner instead if you don’t keep the Arc in the Err case. Immediately dropping the Err-value, as the expression Arc::try_unwrap(this).ok() does, can cause the strong count to drop to zero and the inner value of the Arc to be dropped. For instance, if two threads execute such an expression in parallel, there is a race condition without the possibility of unsafety: The threads could first both check whether they own the last instance in Arc::try_unwrap, determine that they both do not, and then both discard and drop their instance in the call to ok. In this scenario, the value inside the Arc is safely destroyed by exactly one of the threads, but neither thread will ever be able to use the value.

Examples

use portable_atomic_util::Arc;

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

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

pub fn into_inner(this: Arc<T>) -> Option<T>

Returns the inner value, if the Arc has exactly one strong reference.

Otherwise, None is returned and the Arc is dropped.

This will succeed even if there are outstanding weak references.

If Arc::into_inner is called on every clone of this Arc, it is guaranteed that exactly one of the calls returns the inner value. This means in particular that the inner value is not dropped.

Arc::try_unwrap is conceptually similar to Arc::into_inner, but it is meant for different use-cases. If used as a direct replacement for Arc::into_inner anyway, such as with the expression Arc::try_unwrap(this).ok(), then it does not give the same guarantee as described in the previous paragraph. For more information, see the examples below and read the documentation of Arc::try_unwrap.

Examples

Minimal example demonstrating the guarantee that Arc::into_inner gives.

use portable_atomic_util::Arc;

let x = Arc::new(3);
let y = Arc::clone(&x);

// Two threads calling `Arc::into_inner` on both clones of an `Arc`:
let x_thread = std::thread::spawn(|| Arc::into_inner(x));
let y_thread = std::thread::spawn(|| Arc::into_inner(y));

let x_inner_value = x_thread.join().unwrap();
let y_inner_value = y_thread.join().unwrap();

// One of the threads is guaranteed to receive the inner value:
assert!(matches!((x_inner_value, y_inner_value), (None, Some(3)) | (Some(3), None)));
// The result could also be `(None, None)` if the threads called
// `Arc::try_unwrap(x).ok()` and `Arc::try_unwrap(y).ok()` instead.

A more practical example demonstrating the need for Arc::into_inner:

use portable_atomic_util::Arc;

// Definition of a simple singly linked list using `Arc`:
#[derive(Clone)]
struct LinkedList<T>(Option<Arc<Node<T>>>);
struct Node<T>(T, Option<Arc<Node<T>>>);

// Dropping a long `LinkedList<T>` relying on the destructor of `Arc`
// can cause a stack overflow. To prevent this, we can provide a
// manual `Drop` implementation that does the destruction in a loop:
impl<T> Drop for LinkedList<T> {
    fn drop(&mut self) {
        let mut link = self.0.take();
        while let Some(arc_node) = link.take() {
            if let Some(Node(_value, next)) = Arc::into_inner(arc_node) {
                link = next;
            }
        }
    }
}

// Implementation of `new` and `push` omitted
impl<T> LinkedList<T> {
    /* ... */
}

// The following code could have still caused a stack overflow
// despite the manual `Drop` impl if that `Drop` impl had used
// `Arc::try_unwrap(arc).ok()` instead of `Arc::into_inner(arc)`.

// Create a long list and clone it
let mut x = LinkedList::new();
let size = 100000;
for i in 0..size {
    x.push(i); // Adds i to the front of x
}
let y = x.clone();

// Drop the clones in parallel
let x_thread = std::thread::spawn(|| drop(x));
let y_thread = std::thread::spawn(|| drop(y));
x_thread.join().unwrap();
y_thread.join().unwrap();

impl<T> Arc<[T]>

pub fn new_uninit_slice(len: usize) -> Arc<[MaybeUninit<T>]>

Constructs a new atomically reference-counted slice with uninitialized contents.

Examples

use portable_atomic_util::Arc;

let mut values = Arc::<[u32]>::new_uninit_slice(3);

// Deferred initialization:
let data = Arc::get_mut(&mut values).unwrap();
data[0].write(1);
data[1].write(2);
data[2].write(3);

let values = unsafe { values.assume_init() };

assert_eq!(*values, [1, 2, 3])

impl<T> Arc<MaybeUninit<T>>

pub unsafe fn assume_init(self) -> Arc<T>

Converts to Arc<T>.

Safety

As with MaybeUninit::assume_init, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.

Examples

use portable_atomic_util::Arc;

let mut five = Arc::<u32>::new_uninit();

// Deferred initialization:
Arc::get_mut(&mut five).unwrap().write(5);

let five = unsafe { five.assume_init() };

assert_eq!(*five, 5)

impl<T> Arc<[MaybeUninit<T>]>

pub unsafe fn assume_init(self) -> Arc<[T]>

Converts to Arc<[T]>.

Safety

As with MaybeUninit::assume_init, it is up to the caller to guarantee that the inner value really is in an initialized state. Calling this when the content is not yet fully initialized causes immediate undefined behavior.

Examples

use portable_atomic_util::Arc;

let mut values = Arc::<[u32]>::new_uninit_slice(3);

// Deferred initialization:
let data = Arc::get_mut(&mut values).unwrap();
data[0].write(1);
data[1].write(2);
data[2].write(3);

let values = unsafe { values.assume_init() };

assert_eq!(*values, [1, 2, 3])

impl<T> Arc<T>

where T: ?Sized,

pub unsafe fn from_raw(ptr: *const T) -> Arc<T>

Constructs an Arc<T> from a raw pointer.

Safety

The raw pointer must have been previously returned by a call to Arc<U>::into_raw with the following requirements:

• If U is sized, it must have the same size and alignment as T. This is trivially true if U is T.
• If U is unsized, its data pointer must have the same size and alignment as T. This is trivially true if Arc<U> was constructed through Arc<T> and then converted to Arc<U> through an unsized coercion.

Note that if U or U’s data pointer is not T but has the same size and alignment, this is basically like transmuting references of different types. See mem::transmute for more information on what restrictions apply in this case.

The user of from_raw has to make sure a specific value of T is only dropped once.

This function is unsafe because improper use may lead to memory unsafety, even if the returned Arc<T> is never accessed.

Examples

use portable_atomic_util::Arc;

let x = Arc::new("hello".to_owned());
let x_ptr = Arc::into_raw(x);

unsafe {
    // Convert back to an `Arc` to prevent leak.
    let x = Arc::from_raw(x_ptr);
    assert_eq!(&*x, "hello");

    // Further calls to `Arc::from_raw(x_ptr)` would be memory-unsafe.
}

// The memory was freed when `x` went out of scope above, so `x_ptr` is now dangling!

Convert a slice back into its original array:

use portable_atomic_util::Arc;

let x: Arc<[u32]> = Arc::from([1, 2, 3]);
let x_ptr: *const [u32] = Arc::into_raw(x);

unsafe {
    let x: Arc<[u32; 3]> = Arc::from_raw(x_ptr.cast::<[u32; 3]>());
    assert_eq!(&*x, &[1, 2, 3]);
}

pub unsafe fn increment_strong_count(ptr: *const T)

Increments the strong reference count on the Arc<T> associated with the provided pointer by one.

Safety

The pointer must have been obtained through Arc::into_raw, and the associated Arc instance must be valid (i.e. the strong count must be at least 1) for the duration of this method.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

unsafe {
    let ptr = Arc::into_raw(five);
    Arc::increment_strong_count(ptr);

    // This assertion is deterministic because we haven't shared
    // the `Arc` between threads.
    let five = Arc::from_raw(ptr);
    assert_eq!(2, Arc::strong_count(&five));
}

pub unsafe fn decrement_strong_count(ptr: *const T)

Decrements the strong reference count on the Arc<T> associated with the provided pointer by one.

Safety

The pointer must have been obtained through Arc::into_raw, and the associated Arc instance must be valid (i.e. the strong count must be at least 1) when invoking this method. This method can be used to release the final Arc and backing storage, but should not be called after the final Arc has been released.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

unsafe {
    let ptr = Arc::into_raw(five);
    Arc::increment_strong_count(ptr);

    // Those assertions are deterministic because we haven't shared
    // the `Arc` between threads.
    let five = Arc::from_raw(ptr);
    assert_eq!(2, Arc::strong_count(&five));
    Arc::decrement_strong_count(ptr);
    assert_eq!(1, Arc::strong_count(&five));
}

impl<T> Arc<T>

where T: ?Sized,

pub fn into_raw(this: Arc<T>) -> *const T

Consumes the Arc, returning the wrapped pointer.

To avoid a memory leak the pointer must be converted back to an Arc using Arc::from_raw.

Examples

use portable_atomic_util::Arc;

let x = Arc::new("hello".to_owned());
let x_ptr = Arc::into_raw(x);
assert_eq!(unsafe { &*x_ptr }, "hello");

pub fn as_ptr(this: &Arc<T>) -> *const T

Provides a raw pointer to the data.

The counts are not affected in any way and the Arc is not consumed. The pointer is valid for as long as there are strong counts in the Arc.

Examples

use portable_atomic_util::Arc;

let x = Arc::new("hello".to_owned());
let y = Arc::clone(&x);
let x_ptr = Arc::as_ptr(&x);
assert_eq!(x_ptr, Arc::as_ptr(&y));
assert_eq!(unsafe { &*x_ptr }, "hello");

pub fn downgrade(this: &Arc<T>) -> Weak<T>

Creates a new Weak pointer to this allocation.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

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

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

Gets the number of Weak pointers to this allocation.

Safety

This method by itself is safe, but using it correctly requires extra care. Another thread can change the weak count at any time, including potentially between calling this method and acting on the result.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);
let _weak_five = Arc::downgrade(&five);

// This assertion is deterministic because we haven't shared
// the `Arc` or `Weak` between threads.
assert_eq!(1, Arc::weak_count(&five));

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

Gets the number of strong (Arc) pointers to this allocation.

Safety

This method by itself is safe, but using it correctly requires extra care. Another thread can change the strong count at any time, including potentially between calling this method and acting on the result.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);
let _also_five = Arc::clone(&five);

// This assertion is deterministic because we haven't shared
// the `Arc` between threads.
assert_eq!(2, Arc::strong_count(&five));

pub fn ptr_eq(this: &Arc<T>, other: &Arc<T>) -> bool

Returns true if the two Arcs point to the same allocation in a vein similar to ptr::eq. This function ignores the metadata of dyn Trait pointers.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);
let same_five = Arc::clone(&five);
let other_five = Arc::new(5);

assert!(Arc::ptr_eq(&five, &same_five));
assert!(!Arc::ptr_eq(&five, &other_five));

impl<T> Arc<T>

where T: CloneToUninit + ?Sized,

pub fn make_mut(this: &mut Arc<T>) -> &mut T

Makes a mutable reference into the given Arc.

If there are other Arc pointers to the same allocation, then make_mut will clone the inner value to a new allocation to ensure unique ownership. This is also referred to as clone-on-write.

However, if there are no other Arc pointers to this allocation, but some Weak pointers, then the Weak pointers will be dissociated and the inner value will not be cloned.

See also get_mut, which will fail rather than cloning the inner value or dissociating Weak pointers.

Examples

use portable_atomic_util::Arc;

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

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

// Now `data` and `other_data` point to different allocations.
assert_eq!(*data, 8);
assert_eq!(*other_data, 12);

Weak pointers will be dissociated:

use portable_atomic_util::Arc;

let mut data = Arc::new(75);
let weak = Arc::downgrade(&data);

assert!(75 == *data);
assert!(75 == *weak.upgrade().unwrap());

*Arc::make_mut(&mut data) += 1;

assert!(76 == *data);
assert!(weak.upgrade().is_none());

impl<T> Arc<T>

where T: Clone,

pub fn unwrap_or_clone(this: Arc<T>) -> T

If we have the only reference to T then unwrap it. Otherwise, clone T and return the clone.

Assuming arc_t is of type Arc<T>, this function is functionally equivalent to (*arc_t).clone(), but will avoid cloning the inner value where possible.

Examples

use portable_atomic_util::Arc;
use std::ptr;

let inner = String::from("test");
let ptr = inner.as_ptr();

let arc = Arc::new(inner);
let inner = Arc::unwrap_or_clone(arc);
// The inner value was not cloned
assert!(ptr::eq(ptr, inner.as_ptr()));

let arc = Arc::new(inner);
let arc2 = arc.clone();
let inner = Arc::unwrap_or_clone(arc);
// Because there were 2 references, we had to clone the inner value.
assert!(!ptr::eq(ptr, inner.as_ptr()));
// `arc2` is the last reference, so when we unwrap it we get back
// the original `String`.
let inner = Arc::unwrap_or_clone(arc2);
assert!(ptr::eq(ptr, inner.as_ptr()));

impl<T> Arc<T>

where T: ?Sized,

pub fn get_mut(this: &mut Arc<T>) -> Option<&mut T>

Returns a mutable reference into the given Arc, if there are no other Arc or Weak pointers to the same allocation.

Returns None otherwise, because it is not safe to mutate a shared value.

See also make_mut, which will clone the inner value when there are other Arc pointers.

Examples

use portable_atomic_util::Arc;

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

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

impl Arc<dyn Any + Sync + Send>

pub fn downcast<T>(self) -> Result<Arc<T>, Arc<dyn Any + Sync + Send>>

where T: Any + Send + Sync,

Attempts to downcast the Arc<dyn Any + Send + Sync> to a concrete type.

Examples

use portable_atomic_util::Arc;
use std::any::Any;

fn print_if_string(value: Arc<dyn Any + Send + Sync>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

let my_string = "Hello World".to_string();
print_if_string(Arc::from(Box::new(my_string) as Box<dyn Any + Send + Sync>));
print_if_string(Arc::from(Box::new(0i8) as Box<dyn Any + Send + Sync>));
// or with "--cfg portable_atomic_unstable_coerce_unsized" in RUSTFLAGS (requires Rust nightly):
// print_if_string(Arc::new(my_string));
// print_if_string(Arc::new(0i8));

Trait Implementations

impl<T> AsRef<T> for Arc<T>

where T: ?Sized,

fn as_ref(&self) -> &T

Converts this type into a shared reference of the (usually inferred) input type.

impl<T> Borrow<T> for Arc<T>

where T: ?Sized,

fn borrow(&self) -> &T

Immutably borrows from an owned value.

impl<T> Clone for Arc<T>

where T: ?Sized,

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

Makes a clone of the Arc pointer.

This creates another pointer to the same allocation, increasing the strong reference count.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

let _ = Arc::clone(&five);

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

Performs copy-assignment from source.

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> Default for Arc<[T]>

fn default() -> Arc<[T]>

Creates an empty [T] inside an Arc.

This may or may not share an allocation with other Arcs.

impl<T> Default for Arc<T>

where T: Default,

fn default() -> Arc<T>

Creates a new Arc<T>, with the Default value for T.

Examples

use portable_atomic_util::Arc;

let x: Arc<i32> = Default::default();
assert_eq!(*x, 0);

impl Default for Arc<str>

fn default() -> Arc<str>

Creates an empty str inside an Arc.

This may or may not share an allocation with other Arcs.

impl<T> Deref for Arc<T>

where T: ?Sized,

type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &<Arc<T> as Deref>::Target

Dereferences the value.

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> Drop for Arc<T>

where T: ?Sized,

fn drop(&mut self)

Drops the Arc.

This will decrement the strong reference count. If the strong reference count reaches zero then the only other references (if any) are Weak, so we drop the inner value.

Examples

use portable_atomic_util::Arc;

struct Foo;

impl Drop for Foo {
    fn drop(&mut self) {
        println!("dropped!");
    }
}

let foo = Arc::new(Foo);
let foo2 = Arc::clone(&foo);

drop(foo); // Doesn't print anything
drop(foo2); // Prints "dropped!"

impl<T> Error for Arc<T>

where T: Error + ?Sized,

fn description(&self) -> &str

👎Deprecated since 1.42.0: use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0: replaced by Error::source, which can support downcasting

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl<T> From<&[T]> for Arc<[T]>

where T: Clone,

fn from(v: &[T]) -> Arc<[T]>

Allocates a reference-counted slice and fills it by cloning v’s items.

Example

use portable_atomic_util::Arc;
let original: &[i32] = &[1, 2, 3];
let shared: Arc<[i32]> = Arc::from(original);
assert_eq!(&[1, 2, 3], &shared[..]);

impl From<&str> for Arc<str>

fn from(v: &str) -> Arc<str>

Allocates a reference-counted str and copies v into it.

Example

use portable_atomic_util::Arc;
let shared: Arc<str> = Arc::from("eggplant");
assert_eq!("eggplant", &shared[..]);

impl<T, const N: usize> From<[T; N]> for Arc<[T]>

fn from(v: [T; N]) -> Arc<[T]>

Converts a [T; N] into an Arc<[T]>.

The conversion moves the array into a newly allocated Arc.

Example

use portable_atomic_util::Arc;
let original: [i32; 3] = [1, 2, 3];
let shared: Arc<[i32]> = Arc::from(original);
assert_eq!(&[1, 2, 3], &shared[..]);

impl From<Arc<str>> for Arc<[u8]>

fn from(rc: Arc<str>) -> Arc<[u8]>

Converts an atomically reference-counted string slice into a byte slice.

Example

use portable_atomic_util::Arc;
let string: Arc<str> = Arc::from("eggplant");
let bytes: Arc<[u8]> = Arc::from(string);
assert_eq!("eggplant".as_bytes(), bytes.as_ref());

impl<T> From<Box<T>> for Arc<T>

where T: ?Sized,

fn from(v: Box<T>) -> Arc<T>

Move a boxed object to a new, reference-counted allocation.

Example

use portable_atomic_util::Arc;
let unique: Box<str> = Box::from("eggplant");
let shared: Arc<str> = Arc::from(unique);
assert_eq!("eggplant", &shared[..]);

impl<'a, B> From<Cow<'a, B>> for Arc<B>

where B: ToOwned + ?Sized, Arc<B>: From<&'a B> + From<<B as ToOwned>::Owned>,

fn from(cow: Cow<'a, B>) -> Arc<B>

Creates an atomically reference-counted pointer from a clone-on-write pointer by copying its content.

Example

use portable_atomic_util::Arc;
use std::borrow::Cow;
let cow: Cow<'_, str> = Cow::Borrowed("eggplant");
let shared: Arc<str> = Arc::from(cow);
assert_eq!("eggplant", &shared[..]);

impl From<String> for Arc<str>

fn from(v: String) -> Arc<str>

Allocates a reference-counted str and copies v into it.

Example

use portable_atomic_util::Arc;
let unique: String = "eggplant".to_owned();
let shared: Arc<str> = Arc::from(unique);
assert_eq!("eggplant", &shared[..]);

impl<T> From<T> for Arc<T>

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

Converts a T into an Arc<T>

The conversion moves the value into a newly allocated Arc. It is equivalent to calling Arc::new(t).

Example

use portable_atomic_util::Arc;
let x = 5;
let arc = Arc::new(5);

assert_eq!(Arc::from(x), arc);

impl<T> From<Vec<T>> for Arc<[T]>

fn from(v: Vec<T>) -> Arc<[T]>

Allocates a reference-counted slice and moves v’s items into it.

Example

use portable_atomic_util::Arc;
let unique: Vec<i32> = vec![1, 2, 3];
let shared: Arc<[i32]> = Arc::from(unique);
assert_eq!(&[1, 2, 3], &shared[..]);

impl<T> FromIterator<T> for Arc<[T]>

fn from_iter<I>(iter: I) -> Arc<[T]>

where I: IntoIterator<Item = T>,

Takes each element in the Iterator and collects it into an Arc<[T]>.

Performance characteristics

The general case

In the general case, collecting into Arc<[T]> is done by first collecting into a Vec<T>. That is, when writing the following:

use portable_atomic_util::Arc;
let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0).collect();

this behaves as if we wrote:

use portable_atomic_util::Arc;
let evens: Arc<[u8]> = (0..10).filter(|&x| x % 2 == 0)
    .collect::<Vec<_>>() // The first set of allocations happens here.
    .into(); // A second allocation for `Arc<[T]>` happens here.

This will allocate as many times as needed for constructing the Vec<T> and then it will allocate once for turning the Vec<T> into the Arc<[T]>.

Iterators of known length

When your Iterator implements TrustedLen and is of an exact size, a single allocation will be made for the Arc<[T]>. For example:

use portable_atomic_util::Arc;
let evens: Arc<[u8]> = (0..10).collect(); // Just a single allocation happens here.

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 given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl<T> Ord for Arc<T>

where T: Ord + ?Sized,

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

Comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;
use std::cmp::Ordering;

let five = Arc::new(5);

assert_eq!(Ordering::Less, five.cmp(&Arc::new(6)));

fn max(self, other: Self) -> Self

where Self: Sized,

Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

where Self: Sized,

Compares and returns the minimum of two values.

fn clamp(self, min: Self, max: Self) -> Self

where Self: Sized,

Restrict a value to a certain interval.

impl<T> PartialEq for Arc<T>

where T: PartialEq + ?Sized,

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

Equality for two Arcs.

Two Arcs are equal if their inner values are equal, even if they are stored in different allocation.

If T also implements Eq (implying reflexivity of equality), two Arcs that point to the same allocation are always equal.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five == Arc::new(5));

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

Inequality for two Arcs.

Two Arcs are not equal if their inner values are not equal.

If T also implements Eq (implying reflexivity of equality), two Arcs that point to the same value are always equal.

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five != Arc::new(6));

impl<T> PartialOrd for Arc<T>

where T: PartialOrd + ?Sized,

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

Partial comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;
use std::cmp::Ordering;

let five = Arc::new(5);

assert_eq!(Some(Ordering::Less), five.partial_cmp(&Arc::new(6)));

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

Less-than comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five < Arc::new(6));

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

‘Less than or equal to’ comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five <= Arc::new(5));

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

Greater-than comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five > Arc::new(4));

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

‘Greater than or equal to’ comparison for two Arcs.

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

Examples

use portable_atomic_util::Arc;

let five = Arc::new(5);

assert!(five >= Arc::new(5));

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, const N: usize> TryFrom<Arc<[T]>> for Arc<[T; N]>

type Error = Arc<[T]>

The type returned in the event of a conversion error.

fn try_from( boxed_slice: Arc<[T]>, ) -> Result<Arc<[T; N]>, <Arc<[T; N]> as TryFrom<Arc<[T]>>>::Error>

Performs the conversion.

impl<T> Eq for Arc<T>

where T: Eq + ?Sized,

impl<T> Send for Arc<T>

where T: Sync + Send + ?Sized,

impl<T> Sync for Arc<T>

where T: Sync + Send + ?Sized,

impl<T> Unpin for Arc<T>

where T: ?Sized,

impl<T> UnwindSafe for Arc<T>

where T: RefUnwindSafe + ?Sized,