#[repr(C, align(8))]pub struct AtomicU64 { /* private fields */ }Expand description
An integer type which can be safely shared between threads.
This type has the same
size and bit validity
as the underlying integer type, u64.
However, the alignment of this type is always equal to its size, even on targets where u64 has a lesser alignment.
For more about the differences between atomic types and non-atomic types as well as information about the portability of this type, please see the module-level documentation.
Note: This type is only available on platforms that support
atomic loads and stores of u64.
Implementations§
source§impl AtomicU64
impl AtomicU64
1.34.0 (const: 1.34.0) · sourcepub const fn new(v: u64) -> Self
pub const fn new(v: u64) -> Self
Creates a new atomic integer.
§Examples
1.75.0 (const: unstable) · sourcepub unsafe fn from_ptr<'a>(ptr: *mut u64) -> &'a AtomicU64
pub unsafe fn from_ptr<'a>(ptr: *mut u64) -> &'a AtomicU64
Creates a new reference to an atomic integer from a pointer.
§Examples
use std::sync::atomic::{self, AtomicU64};
// Get a pointer to an allocated value
let ptr: *mut u64 = Box::into_raw(Box::new(0));
assert!(ptr.cast::<AtomicU64>().is_aligned());
{
// Create an atomic view of the allocated value
let atomic = unsafe {AtomicU64::from_ptr(ptr) };
// Use `atomic` for atomic operations, possibly share it with other threads
atomic.store(1, 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_eq!(unsafe { *ptr }, 1);
// Deallocate the value
unsafe { drop(Box::from_raw(ptr)) }§Safety
ptrmust be aligned toalign_of::<AtomicU64>()(note that on some platforms this can be bigger thanalign_of::<u64>()).ptrmust 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.
1.34.0 · sourcepub fn get_mut(&mut self) -> &mut u64
pub fn get_mut(&mut self) -> &mut u64
Returns a mutable reference to the underlying integer.
This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.
§Examples
sourcepub fn get_mut_slice(this: &mut [Self]) -> &mut [u64]
🔬This is a nightly-only experimental API. (atomic_from_mut #76314)
pub fn get_mut_slice(this: &mut [Self]) -> &mut [u64]
atomic_from_mut #76314)Get non-atomic access to a &mut [AtomicU64] slice
This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.
§Examples
#![feature(atomic_from_mut)]
use std::sync::atomic::{AtomicU64, Ordering};
let mut some_ints = [const { AtomicU64::new(0) }; 10];
let view: &mut [u64] = AtomicU64::get_mut_slice(&mut some_ints);
assert_eq!(view, [0; 10]);
view
.iter_mut()
.enumerate()
.for_each(|(idx, int)| *int = idx as _);
std::thread::scope(|s| {
some_ints
.iter()
.enumerate()
.for_each(|(idx, int)| {
s.spawn(move || assert_eq!(int.load(Ordering::Relaxed), idx as _));
})
});1.34.0 (const: 1.79.0) · sourcepub const fn into_inner(self) -> u64
pub const fn into_inner(self) -> u64
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
1.34.0 · sourcepub fn load(&self, order: Ordering) -> u64
pub fn load(&self, order: Ordering) -> u64
1.34.0 · sourcepub fn store(&self, val: u64, order: Ordering)
pub fn store(&self, val: u64, order: Ordering)
1.34.0 · sourcepub fn swap(&self, val: u64, order: Ordering) -> u64
pub fn swap(&self, val: u64, order: Ordering) -> u64
Stores a value into the atomic integer, 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
u64.
§Examples
1.34.0 · sourcepub fn compare_and_swap(&self, current: u64, new: u64, order: Ordering) -> u64
👎Deprecated since 1.50.0: Use compare_exchange or compare_exchange_weak instead
pub fn compare_and_swap(&self, current: u64, new: u64, order: Ordering) -> u64
compare_exchange or compare_exchange_weak insteadStores a value into the atomic integer 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
u64.
§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::{AtomicU64, Ordering};
let some_var = AtomicU64::new(5);
assert_eq!(some_var.compare_and_swap(5, 10, Ordering::Relaxed), 5);
assert_eq!(some_var.load(Ordering::Relaxed), 10);
assert_eq!(some_var.compare_and_swap(6, 12, Ordering::Relaxed), 10);
assert_eq!(some_var.load(Ordering::Relaxed), 10);1.34.0 · sourcepub fn compare_exchange(
&self,
current: u64,
new: u64,
success: Ordering,
failure: Ordering,
) -> Result<u64, u64>
pub fn compare_exchange( &self, current: u64, new: u64, success: Ordering, failure: Ordering, ) -> Result<u64, u64>
Stores a value into the atomic integer 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
u64.
§Examples
use std::sync::atomic::{AtomicU64, Ordering};
let some_var = AtomicU64::new(5);
assert_eq!(some_var.compare_exchange(5, 10,
Ordering::Acquire,
Ordering::Relaxed),
Ok(5));
assert_eq!(some_var.load(Ordering::Relaxed), 10);
assert_eq!(some_var.compare_exchange(6, 12,
Ordering::SeqCst,
Ordering::Acquire),
Err(10));
assert_eq!(some_var.load(Ordering::Relaxed), 10);1.34.0 · sourcepub fn compare_exchange_weak(
&self,
current: u64,
new: u64,
success: Ordering,
failure: Ordering,
) -> Result<u64, u64>
pub fn compare_exchange_weak( &self, current: u64, new: u64, success: Ordering, failure: Ordering, ) -> Result<u64, u64>
Stores a value into the atomic integer if the current value is the same as
the current value.
Unlike AtomicU64::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
u64.
§Examples
1.34.0 · sourcepub fn fetch_add(&self, val: u64, order: Ordering) -> u64
pub fn fetch_add(&self, val: u64, order: Ordering) -> u64
Adds to the current value, returning the previous value.
This operation wraps around on overflow.
fetch_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
u64.
§Examples
1.34.0 · sourcepub fn fetch_sub(&self, val: u64, order: Ordering) -> u64
pub fn fetch_sub(&self, val: u64, order: Ordering) -> u64
Subtracts from the current value, returning the previous value.
This operation wraps around on overflow.
fetch_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
u64.
§Examples
1.34.0 · sourcepub fn fetch_and(&self, val: u64, order: Ordering) -> u64
pub fn fetch_and(&self, val: u64, order: Ordering) -> u64
Bitwise “and” with the current value.
Performs a bitwise “and” operation on the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
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
u64.
§Examples
1.34.0 · sourcepub fn fetch_nand(&self, val: u64, order: Ordering) -> u64
pub fn fetch_nand(&self, val: u64, order: Ordering) -> u64
Bitwise “nand” with the current value.
Performs a bitwise “nand” operation on the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
fetch_nand 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
u64.
§Examples
1.34.0 · sourcepub fn fetch_or(&self, val: u64, order: Ordering) -> u64
pub fn fetch_or(&self, val: u64, order: Ordering) -> u64
Bitwise “or” with the current value.
Performs a bitwise “or” operation on the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
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
u64.
§Examples
1.34.0 · sourcepub fn fetch_xor(&self, val: u64, order: Ordering) -> u64
pub fn fetch_xor(&self, val: u64, order: Ordering) -> u64
Bitwise “xor” with the current value.
Performs a bitwise “xor” operation on the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
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
u64.
§Examples
1.45.0 · sourcepub fn fetch_update<F>(
&self,
set_order: Ordering,
fetch_order: Ordering,
f: F,
) -> Result<u64, u64>
pub fn fetch_update<F>( &self, set_order: Ordering, fetch_order: Ordering, f: F, ) -> Result<u64, u64>
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
AtomicU64::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
u64.
§Considerations
This method is not magic; it is not provided by the hardware.
It is implemented in terms of
AtomicU64::compare_exchange_weak,
and suffers from the same drawbacks.
In particular, this method will not circumvent the ABA Problem.
§Examples
use std::sync::atomic::{AtomicU64, Ordering};
let x = AtomicU64::new(7);
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |_| None), Err(7));
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(7));
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(x + 1)), Ok(8));
assert_eq!(x.load(Ordering::SeqCst), 9);1.45.0 · sourcepub fn fetch_max(&self, val: u64, order: Ordering) -> u64
pub fn fetch_max(&self, val: u64, order: Ordering) -> u64
Maximum with the current value.
Finds the maximum of the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
fetch_max 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
u64.
§Examples
use std::sync::atomic::{AtomicU64, Ordering};
let foo = AtomicU64::new(23);
assert_eq!(foo.fetch_max(42, Ordering::SeqCst), 23);
assert_eq!(foo.load(Ordering::SeqCst), 42);If you want to obtain the maximum value in one step, you can use the following:
1.45.0 · sourcepub fn fetch_min(&self, val: u64, order: Ordering) -> u64
pub fn fetch_min(&self, val: u64, order: Ordering) -> u64
Minimum with the current value.
Finds the minimum of the current value and the argument val, and
sets the new value to the result.
Returns the previous value.
fetch_min 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
u64.
§Examples
use std::sync::atomic::{AtomicU64, Ordering};
let foo = AtomicU64::new(23);
assert_eq!(foo.fetch_min(42, Ordering::Relaxed), 23);
assert_eq!(foo.load(Ordering::Relaxed), 23);
assert_eq!(foo.fetch_min(22, Ordering::Relaxed), 23);
assert_eq!(foo.load(Ordering::Relaxed), 22);If you want to obtain the minimum value in one step, you can use the following:
1.70.0 (const: 1.70.0) · sourcepub const fn as_ptr(&self) -> *mut u64
pub const fn as_ptr(&self) -> *mut u64
Returns a mutable pointer to the underlying integer.
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 u64 instead of &AtomicU64.
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.
§Examples
use std::sync::atomic::AtomicU64;
extern "C" {
fn my_atomic_op(arg: *mut u64);
}
let atomic = AtomicU64::new(1);
// SAFETY: Safe as long as `my_atomic_op` is atomic.
unsafe {
my_atomic_op(atomic.as_ptr());
}