#[repr(C, align(8))]pub struct AtomicPtr<T> { /* private fields */ }
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.
Implementations§
source§impl<T> AtomicPtr<T>
impl<T> AtomicPtr<T>
1.75.0 (const: unstable) · sourcepub unsafe fn from_ptr<'a>(ptr: *mut *mut T) -> &'a AtomicPtr<T>
pub unsafe fn from_ptr<'a>(ptr: *mut *mut T) -> &'a AtomicPtr<T>
Creates a new AtomicPtr
from a pointer.
§Examples
#![feature(pointer_is_aligned)]
use std::sync::atomic::{self, AtomicPtr};
use std::mem::align_of;
// Get a pointer to an allocated value
let ptr: *mut *mut u8 = Box::into_raw(Box::new(std::ptr::null_mut()));
assert!(ptr.is_aligned_to(align_of::<AtomicPtr<u8>>()));
{
// Create an atomic view of the allocated value
let atomic = unsafe { AtomicPtr::from_ptr(ptr) };
// Use `atomic` for atomic operations, possibly share it with other threads
atomic.store(std::ptr::NonNull::dangling().as_ptr(), atomic::Ordering::Relaxed);
}
// It's ok to non-atomically access the value behind `ptr`,
// since the reference to the atomic ended its lifetime in the block above
assert!(!unsafe { *ptr }.is_null());
// Deallocate the value
unsafe { drop(Box::from_raw(ptr)) }
Run§Safety
ptr
must be aligned toalign_of::<AtomicPtr<T>>()
(note that on some platforms this can be bigger thanalign_of::<*mut T>()
).ptr
must be valid for both reads and writes for the whole lifetime'a
.- You must adhere to the Memory model for atomic accesses. In particular, it is not allowed to mix atomic and non-atomic accesses, or atomic accesses of different sizes, without synchronization.
1.15.0 · sourcepub fn get_mut(&mut self) -> &mut *mut T
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);
Runsourcepub fn from_mut(v: &mut *mut T) -> &mut Self
🔬This is a nightly-only experimental API. (atomic_from_mut
#76314)
pub fn from_mut(v: &mut *mut T) -> &mut Self
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);
Runsourcepub fn get_mut_slice(this: &mut [Self]) -> &mut [*mut T]
🔬This is a nightly-only experimental API. (atomic_from_mut
#76314)
pub fn get_mut_slice(this: &mut [Self]) -> &mut [*mut T]
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)]
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}!");
});
}
});
Runsourcepub fn from_mut_slice(v: &mut [*mut T]) -> &mut [Self]
🔬This is a nightly-only experimental API. (atomic_from_mut
#76314)
pub fn from_mut_slice(v: &mut [*mut T]) -> &mut [Self]
atomic_from_mut
#76314)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}!");
}
Run1.15.0 (const: unstable) · sourcepub fn into_inner(self) -> *mut T
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);
Runsourcepub fn load(&self, order: Ordering) -> *mut T
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);
Runsourcepub fn store(&self, ptr: *mut T, order: Ordering)
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);
Runsourcepub fn swap(&self, ptr: *mut T, order: Ordering) -> *mut T
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);
Runsourcepub 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
pub fn compare_and_swap( &self, current: *mut T, new: *mut T, order: Ordering ) -> *mut T
compare_exchange
or compare_exchange_weak
insteadStores 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);
Run1.10.0 · sourcepub fn compare_exchange(
&self,
current: *mut T,
new: *mut T,
success: Ordering,
failure: Ordering
) -> Result<*mut T, *mut T>
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
.
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);
Run1.10.0 · sourcepub fn compare_exchange_weak(
&self,
current: *mut T,
new: *mut T,
success: Ordering,
failure: Ordering
) -> Result<*mut T, *mut T>
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
.
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,
}
}
Run1.53.0 · sourcepub fn fetch_update<F>(
&self,
set_order: Ordering,
fetch_order: Ordering,
f: F
) -> Result<*mut T, *mut T>
pub fn fetch_update<F>( &self, set_order: Ordering, fetch_order: Ordering, f: F ) -> Result<*mut T, *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
.
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);
Runsourcepub fn fetch_ptr_add(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_ptr_add(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Runsourcepub fn fetch_ptr_sub(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_ptr_sub(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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]));
Runsourcepub fn fetch_byte_add(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_byte_add(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Runsourcepub fn fetch_byte_sub(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_byte_sub(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Runsourcepub fn fetch_or(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_or(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Runsourcepub fn fetch_and(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_and(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Runsourcepub fn fetch_xor(&self, val: usize, order: Ordering) -> *mut T
🔬This is a nightly-only experimental API. (strict_provenance_atomic_ptr
#99108)
pub fn fetch_xor(&self, val: usize, order: Ordering) -> *mut T
strict_provenance_atomic_ptr
#99108)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);
Run1.70.0 (const: 1.70.0) · sourcepub const fn as_ptr(&self) -> *mut *mut T
pub const fn as_ptr(&self) -> *mut *mut T
Returns a mutable pointer to the underlying pointer.
Doing non-atomic reads and writes on the resulting integer can be a data race.
This method is mostly useful for FFI, where the function signature may use
*mut *mut T
instead of &AtomicPtr<T>
.
Returning an *mut
pointer from a shared reference to this atomic is safe because the
atomic types work with interior mutability. All modifications of an atomic change the value
through a shared reference, and can do so safely as long as they use atomic operations. Any
use of the returned raw pointer requires an unsafe
block and still has to uphold the same
restriction: operations on it must be atomic.