Struct AtomicUsize

#[repr(C, align(8))]
pub struct AtomicUsize { /* private fields */ }

⚛️ ?core An unsigned integer type which can be safely shared between threads.

Re-exported either from core or from the portable-atomic crate.

---

An integer type which can be safely shared between threads.

This type has the same in-memory representation as the underlying integer type, usize.

If the compiler and the platform support atomic loads and stores of usize, this type is a wrapper for the standard library’s AtomicUsize. If the platform supports it but the compiler does not, atomic operations are implemented using inline assembly. Otherwise synchronizes using global locks. You can call AtomicUsize::is_lock_free() to check whether atomic instructions or locks will be used.

Implementations

impl AtomicUsize

pub const fn new(v: usize) -> AtomicUsize

Creates a new atomic integer.

Examples

use portable_atomic::AtomicUsize;

let atomic_forty_two = AtomicUsize::new(42);

pub const unsafe fn from_ptr<'a>(ptr: *mut usize) -> &'a AtomicUsize

Creates a new reference to an atomic integer from a pointer.

This is const fn on Rust 1.83+.

Safety

• ptr must be aligned to align_of::<AtomicUsize>() (note that on some platforms this can be bigger than align_of::<usize>()).
• ptr must be valid for both reads and writes for the whole lifetime 'a.
• If this atomic type is lock-free, non-atomic accesses to the value behind ptr must have a happens-before relationship with atomic accesses via the returned value (or vice-versa).
  • In other words, time periods where the value is accessed atomically may not overlap with periods where the value is accessed non-atomically.
  • This requirement is trivially satisfied if ptr is never used non-atomically for the duration of lifetime 'a. Most use cases should be able to follow this guideline.
  • This requirement is also trivially satisfied if all accesses (atomic or not) are done from the same thread.
• If this atomic type is not lock-free:
  • Any accesses to the value behind ptr must have a happens-before relationship with accesses via the returned value (or vice-versa).
  • Any concurrent accesses to the value behind ptr for the duration of lifetime 'a must be compatible with operations performed by this atomic type.
• This method must not be used to create overlapping or mixed-size atomic accesses, as these are not supported by the memory model.

pub fn is_lock_free() -> bool

Returns true if operations on values of this type are lock-free.

If the compiler or the platform doesn’t support the necessary atomic instructions, global locks for every potentially concurrent atomic operation will be used.

Examples

use portable_atomic::AtomicUsize;

let is_lock_free = AtomicUsize::is_lock_free();

pub const fn is_always_lock_free() -> bool

Returns true if operations on values of this type are lock-free.

If the compiler or the platform doesn’t support the necessary atomic instructions, global locks for every potentially concurrent atomic operation will be used.

Note: If the atomic operation relies on dynamic CPU feature detection, this type may be lock-free even if the function returns false.

Examples

use portable_atomic::AtomicUsize;

const IS_ALWAYS_LOCK_FREE: bool = AtomicUsize::is_always_lock_free();

pub const fn get_mut(&mut self) -> &mut usize

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.

This is const fn on Rust 1.83+.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let mut some_var = AtomicUsize::new(10);
assert_eq!(*some_var.get_mut(), 10);
*some_var.get_mut() = 5;
assert_eq!(some_var.load(Ordering::SeqCst), 5);

pub const fn into_inner(self) -> usize

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.

This is const fn on Rust 1.56+.

Examples

use portable_atomic::AtomicUsize;

let some_var = AtomicUsize::new(5);
assert_eq!(some_var.into_inner(), 5);

pub fn load(&self, order: Ordering) -> usize

Loads a value from the atomic integer.

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 portable_atomic::{AtomicUsize, Ordering};

let some_var = AtomicUsize::new(5);

assert_eq!(some_var.load(Ordering::Relaxed), 5);

pub fn store(&self, val: usize, order: Ordering)

Stores a value into the atomic integer.

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 portable_atomic::{AtomicUsize, Ordering};

let some_var = AtomicUsize::new(5);

some_var.store(10, Ordering::Relaxed);
assert_eq!(some_var.load(Ordering::Relaxed), 10);

pub fn swap(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let some_var = AtomicUsize::new(5);

assert_eq!(some_var.swap(10, Ordering::Relaxed), 5);

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

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].

Panics

Panics if failure is [Release], [AcqRel].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let some_var = AtomicUsize::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);

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

Stores a value into the atomic integer if the current value is the same as the current value. Unlike 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].

Panics

Panics if failure is [Release], [AcqRel].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let val = AtomicUsize::new(4);

let mut old = val.load(Ordering::Relaxed);
loop {
    let new = old * 2;
    match val.compare_exchange_weak(old, new, Ordering::SeqCst, Ordering::Relaxed) {
        Ok(_) => break,
        Err(x) => old = x,
    }
}

pub fn fetch_add(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0);
assert_eq!(foo.fetch_add(10, Ordering::SeqCst), 0);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn add(&self, val: usize, order: Ordering)

Adds to the current value.

This operation wraps around on overflow.

Unlike fetch_add, this does not return the previous value.

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].

This function may generate more efficient code than fetch_add on some platforms.

• MSP430: add instead of disabling interrupts ({8,16}-bit atomics)

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0);
foo.add(10, Ordering::SeqCst);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn fetch_sub(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(20);
assert_eq!(foo.fetch_sub(10, Ordering::SeqCst), 20);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn sub(&self, val: usize, order: Ordering)

Subtracts from the current value.

This operation wraps around on overflow.

Unlike fetch_sub, this does not return the previous value.

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].

This function may generate more efficient code than fetch_sub on some platforms.

• MSP430: sub instead of disabling interrupts ({8,16}-bit atomics)

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(20);
foo.sub(10, Ordering::SeqCst);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn fetch_and(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b100001);

pub fn and(&self, val: usize, order: Ordering)

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.

Unlike fetch_and, this does not return the previous value.

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].

This function may generate more efficient code than fetch_and on some platforms.

• x86/x86_64: lock and instead of cmpxchg loop ({8,16,32}-bit atomics on x86, but additionally 64-bit atomics on x86_64)
• MSP430: and instead of disabling interrupts ({8,16}-bit atomics)

Note: On x86/x86_64, the use of either function should not usually affect the generated code, because LLVM can properly optimize the case where the result is unused.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b100001);

pub fn fetch_nand(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0x13);
assert_eq!(foo.fetch_nand(0x31, Ordering::SeqCst), 0x13);
assert_eq!(foo.load(Ordering::SeqCst), !(0x13 & 0x31));

pub fn fetch_or(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b111111);

pub fn or(&self, val: usize, order: Ordering)

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.

Unlike fetch_or, this does not return the previous value.

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].

This function may generate more efficient code than fetch_or on some platforms.

• x86/x86_64: lock or instead of cmpxchg loop ({8,16,32}-bit atomics on x86, but additionally 64-bit atomics on x86_64)
• MSP430: or instead of disabling interrupts ({8,16}-bit atomics)

Note: On x86/x86_64, the use of either function should not usually affect the generated code, because LLVM can properly optimize the case where the result is unused.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b111111);

pub fn fetch_xor(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
assert_eq!(foo.fetch_xor(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b011110);

pub fn xor(&self, val: usize, order: Ordering)

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.

Unlike fetch_xor, this does not return the previous value.

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].

This function may generate more efficient code than fetch_xor on some platforms.

• x86/x86_64: lock xor instead of cmpxchg loop ({8,16,32}-bit atomics on x86, but additionally 64-bit atomics on x86_64)
• MSP430: xor instead of disabling interrupts ({8,16}-bit atomics)

Note: On x86/x86_64, the use of either function should not usually affect the generated code, because LLVM can properly optimize the case where the result is unused.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b101101);
foo.xor(0b110011, Ordering::SeqCst);
assert_eq!(foo.load(Ordering::SeqCst), 0b011110);

pub fn fetch_update<F>( &self, set_order: Ordering, fetch_order: Ordering, f: F, ) -> Result<usize, usize>

where F: FnMut(usize) -> Option<usize>,

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 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].

Panics

Panics if fetch_order is [Release], [AcqRel].

Considerations

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

Examples

use portable_atomic::{AtomicUsize, Ordering};

let x = AtomicUsize::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);

pub fn fetch_max(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::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:

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(23);
let bar = 42;
let max_foo = foo.fetch_max(bar, Ordering::SeqCst).max(bar);
assert!(max_foo == 42);

pub fn fetch_min(&self, val: usize, order: Ordering) -> usize

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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::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:

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(23);
let bar = 12;
let min_foo = foo.fetch_min(bar, Ordering::SeqCst).min(bar);
assert_eq!(min_foo, 12);

pub fn bit_set(&self, bit: u32, order: Ordering) -> bool

Sets the bit at the specified bit-position to 1.

Returns true if the specified bit was previously set to 1.

bit_set 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].

This corresponds to x86’s lock bts, and the implementation calls them on x86/x86_64.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b0000);
assert!(!foo.bit_set(0, Ordering::Relaxed));
assert_eq!(foo.load(Ordering::Relaxed), 0b0001);
assert!(foo.bit_set(0, Ordering::Relaxed));
assert_eq!(foo.load(Ordering::Relaxed), 0b0001);

pub fn bit_clear(&self, bit: u32, order: Ordering) -> bool

Clears the bit at the specified bit-position to 1.

Returns true if the specified bit was previously set to 1.

bit_clear 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].

This corresponds to x86’s lock btr, and the implementation calls them on x86/x86_64.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b0001);
assert!(foo.bit_clear(0, Ordering::Relaxed));
assert_eq!(foo.load(Ordering::Relaxed), 0b0000);

pub fn bit_toggle(&self, bit: u32, order: Ordering) -> bool

Toggles the bit at the specified bit-position.

Returns true if the specified bit was previously set to 1.

bit_toggle 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].

This corresponds to x86’s lock btc, and the implementation calls them on x86/x86_64.

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0b0000);
assert!(!foo.bit_toggle(0, Ordering::Relaxed));
assert_eq!(foo.load(Ordering::Relaxed), 0b0001);
assert!(foo.bit_toggle(0, Ordering::Relaxed));
assert_eq!(foo.load(Ordering::Relaxed), 0b0000);

pub fn fetch_not(&self, order: Ordering) -> usize

Logical negates the current value, and sets the new value to the result.

Returns the previous value.

fetch_not 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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0);
assert_eq!(foo.fetch_not(Ordering::Relaxed), 0);
assert_eq!(foo.load(Ordering::Relaxed), !0);

pub fn not(&self, order: Ordering)

Logical negates the current value, and sets the new value to the result.

Unlike fetch_not, this does not return the previous value.

not 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].

This function may generate more efficient code than fetch_not on some platforms.

• x86/x86_64: lock not instead of cmpxchg loop ({8,16,32}-bit atomics on x86, but additionally 64-bit atomics on x86_64)
• MSP430: inv instead of disabling interrupts ({8,16}-bit atomics)

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(0);
foo.not(Ordering::Relaxed);
assert_eq!(foo.load(Ordering::Relaxed), !0);

pub fn fetch_neg(&self, order: Ordering) -> usize

Negates the current value, and sets the new value to the result.

Returns the previous value.

fetch_neg 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].

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(5);
assert_eq!(foo.fetch_neg(Ordering::Relaxed), 5);
assert_eq!(foo.load(Ordering::Relaxed), 5_usize.wrapping_neg());
assert_eq!(foo.fetch_neg(Ordering::Relaxed), 5_usize.wrapping_neg());
assert_eq!(foo.load(Ordering::Relaxed), 5);

pub fn neg(&self, order: Ordering)

Negates the current value, and sets the new value to the result.

Unlike fetch_neg, this does not return the previous value.

neg 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].

This function may generate more efficient code than fetch_neg on some platforms.

• x86/x86_64: lock neg instead of cmpxchg loop ({8,16,32}-bit atomics on x86, but additionally 64-bit atomics on x86_64)

Examples

use portable_atomic::{AtomicUsize, Ordering};

let foo = AtomicUsize::new(5);
foo.neg(Ordering::Relaxed);
assert_eq!(foo.load(Ordering::Relaxed), 5_usize.wrapping_neg());
foo.neg(Ordering::Relaxed);
assert_eq!(foo.load(Ordering::Relaxed), 5);

pub const fn as_ptr(&self) -> *mut usize

Returns a mutable pointer to the underlying integer.

Returning an *mut pointer from a shared reference to this atomic is safe because the atomic types work with interior mutability. Any use of the returned raw pointer requires an unsafe block and has to uphold the safety requirements. If there is concurrent access, note the following additional safety requirements:

• If this atomic type is lock-free, any concurrent operations on it must be atomic.
• Otherwise, any concurrent operations on it must be compatible with operations performed by this atomic type.

This is const fn on Rust 1.58+.

Trait Implementations

impl BitSized<64> for AtomicUsize

const BIT_SIZE: usize = _

The bit size of this type (only the relevant data part, without padding).

const MIN_BYTE_SIZE: usize = _

The rounded up byte size for this type.

fn bit_size(&self) -> usize

Returns the bit size of this type (only the relevant data part, without padding).

fn min_byte_size(&self) -> usize

Returns the rounded up byte size for this type.

impl ConstDefault for AtomicUsize

const DEFAULT: Self

Returns the compile-time “default value” for a type.

impl Debug for AtomicUsize

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

Formats the value using the given formatter.

impl Default for AtomicUsize

fn default() -> AtomicUsize

Returns the “default value” for a type.

impl From<usize> for AtomicUsize

fn from(v: usize) -> AtomicUsize

Converts to this type from the input type.

impl RefUnwindSafe for AtomicUsize