Struct voluntary_servitude::atomics::AtomicOption

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pub struct AtomicOption<T>(_, _);

Expand description

Atomic Option<Box<T>>

It can’t provide a reference to the current value since it may be dropped at any time

You must swap the element to access it

FillOnceAtomicOption provides a API that enables access to the reference, but only enables try_store to write to it

Implementations

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impl<T> AtomicOption<T>

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pub fn new<V>(value: V) -> Selfwhere
V: Into<Option<Box<T>>>,

Creates new AtomicOption

let empty: AtomicOption<()> = AtomicOption::new(None);
assert!(empty.into_inner().is_none());

let filled = AtomicOption::new(Box::new(10));
assert_eq!(filled.into_inner().map(|a| *a), Some(10));

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pub fn try_store<V>(&self, new: V, order: Ordering) -> Result<(), NotEmpty>where
V: Into<Box<T>>,

Stores new value if AtomicOption currently contains a None

This operation is implemented as a single atomic compare_and_swap.

use std::sync::atomic::Ordering;
let option = AtomicOption::default();
let old = option.try_store(5, Ordering::SeqCst);
assert!(old.is_ok());

let failed_to_store = option.try_store(10, Ordering::SeqCst);
assert!(failed_to_store.is_err());
assert_eq!(option.into_inner().map(|a| *a), Some(5));

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pub fn store<V>(&self, new: V, order: Ordering)where
V: Into<Option<Box<T>>>,

Stores value into AtomicOption and drops old one

use std::sync::atomic::Ordering;
let option: AtomicOption<u8> = AtomicOption::new(None);
option.store(Box::new(3), Ordering::SeqCst);
assert_eq!(option.into_inner().map(|a| *a), Some(3));

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pub fn swap<V>(&self, new: V, order: Ordering) -> Option<Box<T>>where
V: Into<Option<Box<T>>>,

Stores value into AtomicOption returning old value

use std::sync::atomic::Ordering;
let option = AtomicOption::default();
assert_eq!(option.swap(Box::new(5), Ordering::SeqCst), None);
assert_eq!(option.swap(None, Ordering::SeqCst), Some(Box::new(5)));

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pub fn take(&self, order: Ordering) -> Option<Box<T>>

Replaces AtomicOption value with None returning old value

use std::sync::atomic::Ordering;
let option = AtomicOption::from(5);
assert_eq!(option.take(Ordering::SeqCst), Some(Box::new(5)));
assert_eq!(option.take(Ordering::SeqCst), None);

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pub unsafe fn atomic_ptr(&self) -> &AtomicPtr<T>

Gives access to inner AtomicPtr (AtomicOption is an abstraction of it).

Safety

This is heavily unsafe.

It’s unsafe because you are responsible for making sure T is not dropped nor replaced with a invalid pointer (or that will be invalidated while still stored).

use std::sync::atomic::Ordering;
let ten = AtomicOption::from(10);
assert_eq!(unsafe { &*ten.atomic_ptr().load(Ordering::SeqCst) }, &10);

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pub fn into_inner(self) -> Option<Box<T>>

Converts itself into a Option<Box<T>>

let ten = AtomicOption::from(10);
assert_eq!(ten.into_inner().map(|a| *a), Some(10));

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pub unsafe fn from_raw(ptr: *mut T) -> Self

Creates new AtomicOption based on raw pointer

Safety

Unsafe because it uses a raw pointer, so it can’t be sure of its origin (and ownership)

You must own the pointer to call this

use std::ptr::null_mut;
let empty = unsafe { AtomicOption::<()>::from_raw(null_mut()) };
assert!(empty.into_inner().is_none());

let filled = unsafe { AtomicOption::from_raw(Box::into_raw(10.into())) };
assert_eq!(filled.into_inner().map(|a| *a), Some(10));

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pub fn get_raw(&self, order: Ordering) -> *mut T

Atomically extracts current pointer stored, this function should probably not be called

Safety

It’s almost never safe to deref this value, it could have been dropped from the moment you extracted it to the moment you deref/access it in any way, it WILL cause UB

It exists to provide a way of implementing safe wrappers (like FillOnceAtomicOption)

use std::{sync::atomic::Ordering, ptr::null_mut};
let empty: AtomicOption<()> = AtomicOption::new(None);
assert_eq!(empty.get_raw(Ordering::SeqCst), null_mut());

let ptr = Box::into_raw(10u8.into());
let filled = unsafe { AtomicOption::from_raw(ptr) };
assert_eq!(filled.get_raw(Ordering::SeqCst), ptr);

// You should probably never deref `ptr`
// You should probably never use this method
// UB will be everywhere, FillOnceAtomicOption is a safe an alternative