Struct AtomicBool

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

A boolean type which can be safely shared between threads.

This type has the same size, alignment, and bit validity as a bool.

Note: This type is only available on platforms that support atomic loads and stores of u8.

Implementations

impl AtomicBool

pub const fn new(v: bool) -> AtomicBool

Creates a new AtomicBool.

Examples

use std::sync::atomic::AtomicBool;

let atomic_true = AtomicBool::new(true);
let atomic_false = AtomicBool::new(false);

pub unsafe fn from_ptr<'a>(ptr: *mut bool) -> &'a AtomicBool

Creates a new AtomicBool from a pointer.

Examples

use std::sync::atomic::{self, AtomicBool};

// Get a pointer to an allocated value
let ptr: *mut bool = Box::into_raw(Box::new(false));

assert!(ptr.cast::<AtomicBool>().is_aligned());

{
    // Create an atomic view of the allocated value
    let atomic = unsafe { AtomicBool::from_ptr(ptr) };

    // Use `atomic` for atomic operations, possibly share it with other threads
    atomic.store(true, 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 }, true);

// Deallocate the value
unsafe { drop(Box::from_raw(ptr)) }

Safety

• ptr must be aligned to align_of::<AtomicBool>() (note that this is always true, since align_of::<AtomicBool>() == 1).
• 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.

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

Returns a mutable reference to the underlying bool.

This is safe because the mutable reference guarantees that no other threads are concurrently accessing the atomic data.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let mut some_bool = AtomicBool::new(true);
assert_eq!(*some_bool.get_mut(), true);
*some_bool.get_mut() = false;
assert_eq!(some_bool.load(Ordering::SeqCst), false);

pub fn from_mut(v: &mut bool) -> &mut Self

🔬This is a nightly-only experimental API. (atomic_from_mut #76314)

Gets atomic access to a &mut bool.

Examples

#![feature(atomic_from_mut)]
use std::sync::atomic::{AtomicBool, Ordering};

let mut some_bool = true;
let a = AtomicBool::from_mut(&mut some_bool);
a.store(false, Ordering::Relaxed);
assert_eq!(some_bool, false);

pub fn get_mut_slice(this: &mut [Self]) -> &mut [bool]

🔬This is a nightly-only experimental API. (atomic_from_mut #76314)

Gets non-atomic access to a &mut [AtomicBool] 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::{AtomicBool, Ordering};

let mut some_bools = [const { AtomicBool::new(false) }; 10];

let view: &mut [bool] = AtomicBool::get_mut_slice(&mut some_bools);
assert_eq!(view, [false; 10]);
view[..5].copy_from_slice(&[true; 5]);

std::thread::scope(|s| {
    for t in &some_bools[..5] {
        s.spawn(move || assert_eq!(t.load(Ordering::Relaxed), true));
    }

    for f in &some_bools[5..] {
        s.spawn(move || assert_eq!(f.load(Ordering::Relaxed), false));
    }
});

pub fn from_mut_slice(v: &mut [bool]) -> &mut [Self]

🔬This is a nightly-only experimental API. (atomic_from_mut #76314)

Gets atomic access to a &mut [bool] slice.

Examples

#![feature(atomic_from_mut)]
use std::sync::atomic::{AtomicBool, Ordering};

let mut some_bools = [false; 10];
let a = &*AtomicBool::from_mut_slice(&mut some_bools);
std::thread::scope(|s| {
    for i in 0..a.len() {
        s.spawn(move || a[i].store(true, Ordering::Relaxed));
    }
});
assert_eq!(some_bools, [true; 10]);

pub const fn into_inner(self) -> bool

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::AtomicBool;

let some_bool = AtomicBool::new(true);
assert_eq!(some_bool.into_inner(), true);

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

Loads a value from the bool.

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::{AtomicBool, Ordering};

let some_bool = AtomicBool::new(true);

assert_eq!(some_bool.load(Ordering::Relaxed), true);

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

Stores a value into the bool.

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::{AtomicBool, Ordering};

let some_bool = AtomicBool::new(true);

some_bool.store(false, Ordering::Relaxed);
assert_eq!(some_bool.load(Ordering::Relaxed), false);

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

Stores a value into the bool, 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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let some_bool = AtomicBool::new(true);

assert_eq!(some_bool.swap(false, Ordering::Relaxed), true);
assert_eq!(some_bool.load(Ordering::Relaxed), false);

pub fn compare_and_swap( &self, current: bool, new: bool, order: Ordering, ) -> bool

👎Deprecated since 1.50.0: Use compare_exchange or compare_exchange_weak instead

Stores a value into the bool 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 u8.

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::{AtomicBool, Ordering};

let some_bool = AtomicBool::new(true);

assert_eq!(some_bool.compare_and_swap(true, false, Ordering::Relaxed), true);
assert_eq!(some_bool.load(Ordering::Relaxed), false);

assert_eq!(some_bool.compare_and_swap(true, true, Ordering::Relaxed), false);
assert_eq!(some_bool.load(Ordering::Relaxed), false);

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

Stores a value into the bool 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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let some_bool = AtomicBool::new(true);

assert_eq!(some_bool.compare_exchange(true,
                                      false,
                                      Ordering::Acquire,
                                      Ordering::Relaxed),
           Ok(true));
assert_eq!(some_bool.load(Ordering::Relaxed), false);

assert_eq!(some_bool.compare_exchange(true, true,
                                      Ordering::SeqCst,
                                      Ordering::Acquire),
           Err(false));
assert_eq!(some_bool.load(Ordering::Relaxed), false);

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

Stores a value into the bool if the current value is the same as the current value.

Unlike AtomicBool::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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let val = AtomicBool::new(false);

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

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

Logical “and” with a boolean value.

Performs a logical “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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_and(false, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), false);

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_and(true, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), true);

let foo = AtomicBool::new(false);
assert_eq!(foo.fetch_and(false, Ordering::SeqCst), false);
assert_eq!(foo.load(Ordering::SeqCst), false);

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

Logical “nand” with a boolean value.

Performs a logical “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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_nand(false, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), true);

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_nand(true, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst) as usize, 0);
assert_eq!(foo.load(Ordering::SeqCst), false);

let foo = AtomicBool::new(false);
assert_eq!(foo.fetch_nand(false, Ordering::SeqCst), false);
assert_eq!(foo.load(Ordering::SeqCst), true);

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

Logical “or” with a boolean value.

Performs a logical “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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_or(false, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), true);

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_or(true, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), true);

let foo = AtomicBool::new(false);
assert_eq!(foo.fetch_or(false, Ordering::SeqCst), false);
assert_eq!(foo.load(Ordering::SeqCst), false);

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

Logical “xor” with a boolean value.

Performs a logical “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 u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_xor(false, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), true);

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_xor(true, Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), false);

let foo = AtomicBool::new(false);
assert_eq!(foo.fetch_xor(false, Ordering::SeqCst), false);
assert_eq!(foo.load(Ordering::SeqCst), false);

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

Logical “not” with a boolean value.

Performs a logical “not” operation on 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.

Note: This method is only available on platforms that support atomic operations on u8.

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let foo = AtomicBool::new(true);
assert_eq!(foo.fetch_not(Ordering::SeqCst), true);
assert_eq!(foo.load(Ordering::SeqCst), false);

let foo = AtomicBool::new(false);
assert_eq!(foo.fetch_not(Ordering::SeqCst), false);
assert_eq!(foo.load(Ordering::SeqCst), true);

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

Returns a mutable pointer to the underlying bool.

Doing non-atomic reads and writes on the resulting boolean can be a data race. This method is mostly useful for FFI, where the function signature may use *mut bool instead of &AtomicBool.

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::AtomicBool;

extern "C" {
    fn my_atomic_op(arg: *mut bool);
}

let mut atomic = AtomicBool::new(true);
unsafe {
    my_atomic_op(atomic.as_ptr());
}

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

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

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 AtomicBool::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 u8.

Considerations

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

Examples

use std::sync::atomic::{AtomicBool, Ordering};

let x = AtomicBool::new(false);
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |_| None), Err(false));
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(!x)), Ok(false));
assert_eq!(x.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |x| Some(!x)), Ok(true));
assert_eq!(x.load(Ordering::SeqCst), false);

Trait Implementations

impl Debug for AtomicBool

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

Formats the value using the given formatter.

impl Default for AtomicBool

fn default() -> Self

Creates an AtomicBool initialized to false.

impl From<bool> for AtomicBool

fn from(b: bool) -> Self

Converts a bool into an AtomicBool.

Examples

use std::sync::atomic::AtomicBool;
let atomic_bool = AtomicBool::from(true);
assert_eq!(format!("{atomic_bool:?}"), "true")

impl RefUnwindSafe for AtomicBool

impl Sync for AtomicBool