Struct core::sync::atomic::AtomicPtr

#[repr(C, align(8))]
pub struct AtomicPtr<T> { /* private fields */ }

A raw pointer type which can be safely shared between threads.

This type has the same in-memory representation as a *mut T.

Note: This type is only available on platforms that support atomic loads and stores of pointers. Its size depends on the target pointer’s size.

Implementations

impl<T> AtomicPtr<T>

pub const fn new(p: *mut T) -> AtomicPtr<T>

Creates a new AtomicPtr.

Examples

use std::sync::atomic::AtomicPtr;

let ptr = &mut 5;
let atomic_ptr  = AtomicPtr::new(ptr);

pub fn get_mut(&mut self) -> &mut *mut T

Returns a mutable reference to the underlying pointer.

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let mut data = 10;
let mut atomic_ptr = AtomicPtr::new(&mut data);
let mut other_data = 5;
*atomic_ptr.get_mut() = &mut other_data;
assert_eq!(unsafe { *atomic_ptr.load(Ordering::SeqCst) }, 5);

pub fn from_mut(v: &mut *mut T) -> &mut Self

🔬 This is a nightly-only experimental API. (atomic_from_mut #76314)

Get atomic access to a pointer.

Examples

#![feature(atomic_from_mut)]
use std::sync::atomic::{AtomicPtr, Ordering};

let mut data = 123;
let mut some_ptr = &mut data as *mut i32;
let a = AtomicPtr::from_mut(&mut some_ptr);
let mut other_data = 456;
a.store(&mut other_data, Ordering::Relaxed);
assert_eq!(unsafe { *some_ptr }, 456);

pub fn get_mut_slice(this: &mut [Self]) -> &mut [*mut T]

🔬 This is a nightly-only experimental API. (atomic_from_mut #76314)

Get non-atomic access to a &mut [AtomicPtr] slice.

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

Examples

#![feature(atomic_from_mut, inline_const, scoped_threads)]
use std::ptr::null_mut;
use std::sync::atomic::{AtomicPtr, Ordering};

let mut some_ptrs = [const { AtomicPtr::new(null_mut::<String>()) }; 10];

let view: &mut [*mut String] = AtomicPtr::get_mut_slice(&mut some_ptrs);
assert_eq!(view, [null_mut::<String>(); 10]);
view
    .iter_mut()
    .enumerate()
    .for_each(|(i, ptr)| *ptr = Box::into_raw(Box::new(format!("iteration#{i}"))));

std::thread::scope(|s| {
    for ptr in &some_ptrs {
        s.spawn(move || {
            let ptr = ptr.load(Ordering::Relaxed);
            assert!(!ptr.is_null());

            let name = unsafe { Box::from_raw(ptr) };
            println!("Hello, {name}!");
        });
    }
});

pub fn from_mut_slice(v: &mut [*mut T]) -> &mut [Self]

🔬 This is a nightly-only experimental API. (atomic_from_mut #76314)

Get atomic access to a slice of pointers.

Examples

#![feature(atomic_from_mut, scoped_threads)]
use std::ptr::null_mut;
use std::sync::atomic::{AtomicPtr, Ordering};

let mut some_ptrs = [null_mut::<String>(); 10];
let a = &*AtomicPtr::from_mut_slice(&mut some_ptrs);
std::thread::scope(|s| {
    for i in 0..a.len() {
        s.spawn(move || {
            let name = Box::new(format!("thread{i}"));
            a[i].store(Box::into_raw(name), Ordering::Relaxed);
        });
    }
});
for p in some_ptrs {
    assert!(!p.is_null());
    let name = unsafe { Box::from_raw(p) };
    println!("Hello, {name}!");
}

pub fn into_inner(self) -> *mut T

Consumes the atomic and returns the contained value.

This is safe because passing self by value guarantees that no other threads are concurrently accessing the atomic data.

Examples

use std::sync::atomic::AtomicPtr;

let mut data = 5;
let atomic_ptr = AtomicPtr::new(&mut data);
assert_eq!(unsafe { *atomic_ptr.into_inner() }, 5);

pub fn load(&self, order: Ordering) -> *mut T

Loads a value from the pointer.

load takes an Ordering argument which describes the memory ordering of this operation. Possible values are SeqCst, Acquire and Relaxed.

Panics

Panics if order is Release or AcqRel.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr = &mut 5;
let some_ptr  = AtomicPtr::new(ptr);

let value = some_ptr.load(Ordering::Relaxed);

pub fn store(&self, ptr: *mut T, order: Ordering)

Stores a value into the pointer.

store takes an Ordering argument which describes the memory ordering of this operation. Possible values are SeqCst, Release and Relaxed.

Panics

Panics if order is Acquire or AcqRel.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr = &mut 5;
let some_ptr  = AtomicPtr::new(ptr);

let other_ptr = &mut 10;

some_ptr.store(other_ptr, Ordering::Relaxed);

pub fn swap(&self, ptr: *mut T, order: Ordering) -> *mut T

Stores a value into the pointer, returning the previous value.

swap takes an Ordering argument which describes the memory ordering of this operation. All ordering modes are possible. Note that using Acquire makes the store part of this operation Relaxed, and using Release makes the load part Relaxed.

Note: This method is only available on platforms that support atomic operations on pointers.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr = &mut 5;
let some_ptr  = AtomicPtr::new(ptr);

let other_ptr = &mut 10;

let value = some_ptr.swap(other_ptr, Ordering::Relaxed);

pub fn compare_and_swap(
    &self,
    current: *mut T,
    new: *mut T,
    order: Ordering
) -> *mut T

👎 Deprecated since 1.50.0:

Use compare_exchange or compare_exchange_weak instead

Stores a value into the pointer if the current value is the same as the current value.

The return value is always the previous value. If it is equal to current, then the value was updated.

compare_and_swap also takes an Ordering argument which describes the memory ordering of this operation. Notice that even when using AcqRel, the operation might fail and hence just perform an Acquire load, but not have Release semantics. Using Acquire makes the store part of this operation Relaxed if it happens, and using Release makes the load part Relaxed.

Note: This method is only available on platforms that support atomic operations on pointers.

Migrating to compare_exchange and compare_exchange_weak

compare_and_swap is equivalent to compare_exchange with the following mapping for memory orderings:

Original	Success	Failure
Relaxed	Relaxed	Relaxed
Acquire	Acquire	Acquire
Release	Release	Relaxed
AcqRel	AcqRel	Acquire
SeqCst	SeqCst	SeqCst

compare_exchange_weak is allowed to fail spuriously even when the comparison succeeds, which allows the compiler to generate better assembly code when the compare and swap is used in a loop.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr = &mut 5;
let some_ptr  = AtomicPtr::new(ptr);

let other_ptr   = &mut 10;

let value = some_ptr.compare_and_swap(ptr, other_ptr, Ordering::Relaxed);

pub fn compare_exchange(
    &self,
    current: *mut T,
    new: *mut T,
    success: Ordering,
    failure: Ordering
) -> Result<*mut T, *mut T>

Stores a value into the pointer if the current value is the same as the current value.

The return value is a result indicating whether the new value was written and containing the previous value. On success this value is guaranteed to be equal to current.

compare_exchange takes two Ordering arguments to describe the memory ordering of this operation. success describes the required ordering for the read-modify-write operation that takes place if the comparison with current succeeds. failure describes the required ordering for the load operation that takes place when the comparison fails. Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the successful load Relaxed. The failure ordering can only be SeqCst, Acquire or Relaxed and must be equivalent to or weaker than the success ordering.

Note: This method is only available on platforms that support atomic operations on pointers.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr = &mut 5;
let some_ptr  = AtomicPtr::new(ptr);

let other_ptr   = &mut 10;

let value = some_ptr.compare_exchange(ptr, other_ptr,
                                      Ordering::SeqCst, Ordering::Relaxed);

pub fn compare_exchange_weak(
    &self,
    current: *mut T,
    new: *mut T,
    success: Ordering,
    failure: Ordering
) -> Result<*mut T, *mut T>

Stores a value into the pointer if the current value is the same as the current value.

Unlike AtomicPtr::compare_exchange, this function is allowed to spuriously fail even when the comparison succeeds, which can result in more efficient code on some platforms. The return value is a result indicating whether the new value was written and containing the previous value.

compare_exchange_weak takes two Ordering arguments to describe the memory ordering of this operation. success describes the required ordering for the read-modify-write operation that takes place if the comparison with current succeeds. failure describes the required ordering for the load operation that takes place when the comparison fails. Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the successful load Relaxed. The failure ordering can only be SeqCst, Acquire or Relaxed and must be equivalent to or weaker than the success ordering.

Note: This method is only available on platforms that support atomic operations on pointers.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let some_ptr = AtomicPtr::new(&mut 5);

let new = &mut 10;
let mut old = some_ptr.load(Ordering::Relaxed);
loop {
    match some_ptr.compare_exchange_weak(old, new, Ordering::SeqCst, Ordering::Relaxed) {
        Ok(_) => break,
        Err(x) => old = x,
    }
}

pub fn fetch_update<F>(
    &self,
    set_order: Ordering,
    fetch_order: Ordering,
    f: F
) -> Result<*mut T, *mut T> where
    F: FnMut(*mut T) -> Option<*mut T>, 

Fetches the value, and applies a function to it that returns an optional new value. Returns a Result of Ok(previous_value) if the function returned Some(_), else Err(previous_value).

Note: This may call the function multiple times if the value has been changed from other threads in the meantime, as long as the function returns Some(_), but the function will have been applied only once to the stored value.

fetch_update takes two Ordering arguments to describe the memory ordering of this operation. The first describes the required ordering for when the operation finally succeeds while the second describes the required ordering for loads. These correspond to the success and failure orderings of AtomicPtr::compare_exchange respectively.

Using Acquire as success ordering makes the store part of this operation Relaxed, and using Release makes the final successful load Relaxed. The (failed) load ordering can only be SeqCst, Acquire or Relaxed and must be equivalent to or weaker than the success ordering.

Note: This method is only available on platforms that support atomic operations on pointers.

Examples

use std::sync::atomic::{AtomicPtr, Ordering};

let ptr: *mut _ = &mut 5;
let some_ptr = AtomicPtr::new(ptr);

let new: *mut _ = &mut 10;
assert_eq!(some_ptr.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |_| None), Err(ptr));
let result = some_ptr.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| {
    if x == ptr {
        Some(new)
    } else {
        None
    }
});
assert_eq!(result, Ok(ptr));
assert_eq!(some_ptr.load(Ordering::SeqCst), new);

Trait Implementations

impl<T> Debug for AtomicPtr<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Default for AtomicPtr<T>

fn default() -> AtomicPtr<T>

Creates a null AtomicPtr<T>.

impl<T> From<*mut T> for AtomicPtr<T>

fn from(p: *mut T) -> Self

Converts a *mut T into an AtomicPtr<T>.

impl<T> Pointer for AtomicPtr<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> RefUnwindSafe for AtomicPtr<T>

impl<T> Send for AtomicPtr<T>

impl<T> Sync for AtomicPtr<T>