Struct serde::lib::core::sync::atomic::AtomicPtr

1.0.0 · source ·
pub struct AtomicPtr<T> {
    p: UnsafeCell<*mut T>,
}
Expand description

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.

Fields

p: UnsafeCell<*mut T>

Implementations

Creates a new AtomicPtr.

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

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

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

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

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)]
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}!");
        });
    }
});
🔬This is a nightly-only experimental API. (atomic_from_mut)

Get atomic access to a slice of pointers.

Examples
#![feature(atomic_from_mut)]
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}!");
}

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);

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);

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);

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);
👎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:

OriginalSuccessFailure
RelaxedRelaxedRelaxed
AcquireAcquireAcquire
ReleaseReleaseRelaxed
AcqRelAcqRelAcquire
SeqCstSeqCstSeqCst

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);

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.

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);

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.

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,
    }
}

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.

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

Considerations

This method is not magic; it is not provided by the hardware. It is implemented in terms of AtomicPtr::compare_exchange_weak, and suffers from the same drawbacks. In particular, this method will not circumvent the ABA Problem.

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

Offsets the pointer’s address by adding val (in units of T), returning the previous pointer.

This is equivalent to using wrapping_add to atomically perform the equivalent of ptr = ptr.wrapping_add(val);.

This method operates in units of T, which means that it cannot be used to offset the pointer by an amount which is not a multiple of size_of::<T>(). This can sometimes be inconvenient, as you may want to work with a deliberately misaligned pointer. In such cases, you may use the fetch_byte_add method instead.

fetch_ptr_add 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 AtomicPtr.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let atom = AtomicPtr::<i64>::new(core::ptr::null_mut());
assert_eq!(atom.fetch_ptr_add(1, Ordering::Relaxed).addr(), 0);
// Note: units of `size_of::<i64>()`.
assert_eq!(atom.load(Ordering::Relaxed).addr(), 8);
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Offsets the pointer’s address by subtracting val (in units of T), returning the previous pointer.

This is equivalent to using wrapping_sub to atomically perform the equivalent of ptr = ptr.wrapping_sub(val);.

This method operates in units of T, which means that it cannot be used to offset the pointer by an amount which is not a multiple of size_of::<T>(). This can sometimes be inconvenient, as you may want to work with a deliberately misaligned pointer. In such cases, you may use the fetch_byte_sub method instead.

fetch_ptr_sub 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 AtomicPtr.

Examples
#![feature(strict_provenance_atomic_ptr)]
use core::sync::atomic::{AtomicPtr, Ordering};

let array = [1i32, 2i32];
let atom = AtomicPtr::new(array.as_ptr().wrapping_add(1) as *mut _);

assert!(core::ptr::eq(
    atom.fetch_ptr_sub(1, Ordering::Relaxed),
    &array[1],
));
assert!(core::ptr::eq(atom.load(Ordering::Relaxed), &array[0]));
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Offsets the pointer’s address by adding val bytes, returning the previous pointer.

This is equivalent to using wrapping_byte_add to atomically perform ptr = ptr.wrapping_byte_add(val).

fetch_byte_add 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 AtomicPtr.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let atom = AtomicPtr::<i64>::new(core::ptr::null_mut());
assert_eq!(atom.fetch_byte_add(1, Ordering::Relaxed).addr(), 0);
// Note: in units of bytes, not `size_of::<i64>()`.
assert_eq!(atom.load(Ordering::Relaxed).addr(), 1);
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Offsets the pointer’s address by subtracting val bytes, returning the previous pointer.

This is equivalent to using wrapping_byte_sub to atomically perform ptr = ptr.wrapping_byte_sub(val).

fetch_byte_sub 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 AtomicPtr.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let atom = AtomicPtr::<i64>::new(core::ptr::invalid_mut(1));
assert_eq!(atom.fetch_byte_sub(1, Ordering::Relaxed).addr(), 1);
assert_eq!(atom.load(Ordering::Relaxed).addr(), 0);
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Performs a bitwise “or” operation on the address of the current pointer, and the argument val, and stores a pointer with provenance of the current pointer and the resulting address.

This is equivalent to using map_addr to atomically perform ptr = ptr.map_addr(|a| a | val). This can be used in tagged pointer schemes to atomically set tag bits.

Caveat: This operation returns the previous value. To compute the stored value without losing provenance, you may use map_addr. For example: a.fetch_or(val).map_addr(|a| a | val).

fetch_or 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 AtomicPtr.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for ptr for details.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let pointer = &mut 3i64 as *mut i64;

let atom = AtomicPtr::<i64>::new(pointer);
// Tag the bottom bit of the pointer.
assert_eq!(atom.fetch_or(1, Ordering::Relaxed).addr() & 1, 0);
// Extract and untag.
let tagged = atom.load(Ordering::Relaxed);
assert_eq!(tagged.addr() & 1, 1);
assert_eq!(tagged.map_addr(|p| p & !1), pointer);
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Performs a bitwise “and” operation on the address of the current pointer, and the argument val, and stores a pointer with provenance of the current pointer and the resulting address.

This is equivalent to using map_addr to atomically perform ptr = ptr.map_addr(|a| a & val). This can be used in tagged pointer schemes to atomically unset tag bits.

Caveat: This operation returns the previous value. To compute the stored value without losing provenance, you may use map_addr. For example: a.fetch_and(val).map_addr(|a| a & val).

fetch_and 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 AtomicPtr.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for ptr for details.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let pointer = &mut 3i64 as *mut i64;
// A tagged pointer
let atom = AtomicPtr::<i64>::new(pointer.map_addr(|a| a | 1));
assert_eq!(atom.fetch_or(1, Ordering::Relaxed).addr() & 1, 1);
// Untag, and extract the previously tagged pointer.
let untagged = atom.fetch_and(!1, Ordering::Relaxed)
    .map_addr(|a| a & !1);
assert_eq!(untagged, pointer);
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr)

Performs a bitwise “xor” operation on the address of the current pointer, and the argument val, and stores a pointer with provenance of the current pointer and the resulting address.

This is equivalent to using map_addr to atomically perform ptr = ptr.map_addr(|a| a ^ val). This can be used in tagged pointer schemes to atomically toggle tag bits.

Caveat: This operation returns the previous value. To compute the stored value without losing provenance, you may use map_addr. For example: a.fetch_xor(val).map_addr(|a| a ^ val).

fetch_xor 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 AtomicPtr.

This API and its claimed semantics are part of the Strict Provenance experiment, see the module documentation for ptr for details.

Examples
#![feature(strict_provenance_atomic_ptr, strict_provenance)]
use core::sync::atomic::{AtomicPtr, Ordering};

let pointer = &mut 3i64 as *mut i64;
let atom = AtomicPtr::<i64>::new(pointer);

// Toggle a tag bit on the pointer.
atom.fetch_xor(1, Ordering::Relaxed);
assert_eq!(atom.load(Ordering::Relaxed).addr() & 1, 1);

Trait Implementations

Formats the value using the given formatter. Read more

Creates a null AtomicPtr<T>.

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

Formats the value using the given formatter.

Auto Trait Implementations

Blanket Implementations

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.