Struct portable_atomic::AtomicU8

#[repr(C, align(1))]
pub struct AtomicU8 { /* private fields */ }

An integer type which can be safely shared between threads.

This type has the same in-memory representation as the underlying integer type, u8.

If the compiler and the platform support atomic loads and stores of u8, this type is a wrapper for the standard library’s AtomicU8. 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 AtomicU8::is_lock_free() to check whether atomic instructions or locks will be used.

Implementations

impl AtomicU8

pub const fn new(v: u8) -> Self

Creates a new atomic integer.

Examples

use portable_atomic::AtomicU8;

let atomic_forty_two = AtomicU8::new(42);

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::AtomicU8;

let is_lock_free = AtomicU8::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::AtomicU8;

const IS_ALWAYS_LOCK_FREE: bool = AtomicU8::is_always_lock_free();

pub fn get_mut(&mut self) -> &mut u8

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

use portable_atomic::{AtomicU8, Ordering};

let mut some_var = AtomicU8::new(10);
assert_eq!(*some_var.get_mut(), 10);
*some_var.get_mut() = 5;
assert_eq!(some_var.load(Ordering::SeqCst), 5);

pub fn into_inner(self) -> u8

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 portable_atomic::AtomicU8;

let some_var = AtomicU8::new(5);
assert_eq!(some_var.into_inner(), 5);

pub fn load(&self, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let some_var = AtomicU8::new(5);

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

pub fn store(&self, val: u8, 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::{AtomicU8, Ordering};

let some_var = AtomicU8::new(5);

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

pub fn swap(&self, val: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let some_var = AtomicU8::new(5);

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

pub fn compare_exchange(
    &self,
    current: u8,
    new: u8,
    success: Ordering,
    failure: Ordering
) -> Result<u8, u8>

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::{AtomicU8, Ordering};

let some_var = AtomicU8::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: u8,
    new: u8,
    success: Ordering,
    failure: Ordering
) -> Result<u8, u8>

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::{AtomicU8, Ordering};

let val = AtomicU8::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: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0);
assert_eq!(foo.fetch_add(10, Ordering::SeqCst), 0);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn add(&self, val: u8, 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

Examples

use portable_atomic::{AtomicU8, Ordering};

let foo = AtomicU8::new(0);
foo.add(10, Ordering::SeqCst);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn fetch_sub(&self, val: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::new(20);
assert_eq!(foo.fetch_sub(10, Ordering::SeqCst), 20);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn sub(&self, val: u8, 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

Examples

use portable_atomic::{AtomicU8, Ordering};

let foo = AtomicU8::new(20);
foo.sub(10, Ordering::SeqCst);
assert_eq!(foo.load(Ordering::SeqCst), 10);

pub fn fetch_and(&self, val: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0b101101);
assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b100001);

pub fn and(&self, val: u8, 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: lock and instead of cmpxchg loop
• MSP430: and instead of disabling interrupts

Note: On x86, 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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0b101101);
assert_eq!(foo.fetch_and(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b100001);

pub fn fetch_nand(&self, val: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::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: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0b101101);
assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b111111);

pub fn or(&self, val: u8, 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: lock or instead of cmpxchg loop
• MSP430: or instead of disabling interrupts

Note: On x86, 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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0b101101);
assert_eq!(foo.fetch_or(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b111111);

pub fn fetch_xor(&self, val: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::new(0b101101);
assert_eq!(foo.fetch_xor(0b110011, Ordering::SeqCst), 0b101101);
assert_eq!(foo.load(Ordering::SeqCst), 0b011110);

pub fn xor(&self, val: u8, 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: lock xor instead of cmpxchg loop
• MSP430: xor instead of disabling interrupts

Note: On x86, 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::{AtomicU8, Ordering};

let foo = AtomicU8::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<u8, u8>where
    F: FnMut(u8) -> Option<u8>,

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::{AtomicU8, Ordering};

let x = AtomicU8::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: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::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::{AtomicU8, Ordering};

let foo = AtomicU8::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: u8, order: Ordering) -> u8

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::{AtomicU8, Ordering};

let foo = AtomicU8::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::{AtomicU8, Ordering};

let foo = AtomicU8::new(23);
let bar = 12;
let min_foo = foo.fetch_min(bar, Ordering::SeqCst).min(bar);
assert_eq!(min_foo, 12);

Trait Implementations

impl Debug for AtomicU8

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

Formats the value using the given formatter.

impl Default for AtomicU8

fn default() -> Self

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for AtomicU8

Available on crate feature serde only.

fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>where
    D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl From<u8> for AtomicU8

fn from(v: u8) -> Self

Converts to this type from the input type.

impl Serialize for AtomicU8

Available on crate feature serde only.

fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>where
    S: Serializer,

Serialize this value into the given Serde serializer.

impl RefUnwindSafe for AtomicU8