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Auto merge of #74532 - fusion-engineering-forks:atomic-from-mut, r=KodrAus

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Add Atomic*::from_mut.

The atomic equivalent of [`Cell::from_mut`](https://doc.rust-lang.org/stable/std/cell/struct.Cell.html#method.from_mut).
This commit is contained in:
bors 2020-09-15 02:09:34 +00:00
commit 715e9340a1
1 changed files with 98 additions and 1 deletions
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99
library/core/src/sync/atomic.rs
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@ -110,6 +110,7 @@ use self::Ordering::*;
use crate::cell::UnsafeCell;
use crate::fmt;
use crate::intrinsics;
use crate::mem::align_of;
use crate::hint::spin_loop;
@ -327,6 +328,27 @@ impl AtomicBool {
unsafe { &mut *(self.v.get() as *mut bool) }
}
/// Get 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);
/// ```
#[inline]
#[unstable(feature = "atomic_from_mut", issue = "76314")]
pub fn from_mut(v: &mut bool) -> &Self {
// SAFETY: the mutable reference guarantees unique ownership, and
// alignment of both `bool` and `Self` is 1.
unsafe { &*(v as *mut bool as *mut Self) }
}
/// Consumes the atomic and returns the contained value.
///
/// This is safe because passing `self` by value guarantees that no other threads are
@ -820,6 +842,30 @@ impl<T> AtomicPtr<T> {
unsafe { &mut *self.p.get() }
}
/// Get atomic access to a pointer.
///
/// # Examples
///
/// ```
/// #![feature(atomic_from_mut)]
/// use std::sync::atomic::{AtomicPtr, Ordering};
///
/// let mut some_ptr = &mut 123 as *mut i32;
/// let a = AtomicPtr::from_mut(&mut some_ptr);
/// a.store(&mut 456, Ordering::Relaxed);
/// assert_eq!(unsafe { *some_ptr }, 456);
/// ```
#[inline]
#[unstable(feature = "atomic_from_mut", issue = "76314")]
pub fn from_mut(v: &mut *mut T) -> &Self {
let [] = [(); align_of::<AtomicPtr<()>>() - align_of::<*mut ()>()];
// SAFETY:
// - the mutable reference guarantees unique ownership.
// - the alignment of `*mut T` and `Self` is the same on all platforms
// supported by rust, as verified above.
unsafe { &*(v as *mut *mut T as *mut Self) }
}
/// Consumes the atomic and returns the contained value.
///
/// This is safe because passing `self` by value guarantees that no other threads are
@ -1104,6 +1150,13 @@ impl<T> From<*mut T> for AtomicPtr<T> {
}
}
#[allow(unused_macros)] // This macro ends up being unused on some architectures.
macro_rules! if_not_8_bit {
(u8, $($tt:tt)*) => { "" };
(i8, $($tt:tt)*) => { "" };
($_:ident, $($tt:tt)*) => { $($tt)* };
}
#[cfg(target_has_atomic_load_store = "8")]
macro_rules! atomic_int {
($cfg_cas:meta,
@ -1115,7 +1168,8 @@ macro_rules! atomic_int {
$stable_nand:meta,
$const_stable:meta,
$stable_init_const:meta,
$s_int_type:expr, $int_ref:expr,
$(from_mut: cfg($from_mut_cfg:meta),)?
$s_int_type:literal, $int_ref:expr,
$extra_feature:expr,
$min_fn:ident, $max_fn:ident,
$align:expr,
@ -1226,6 +1280,45 @@ assert_eq!(some_var.load(Ordering::SeqCst), 5);
}
}
doc_comment! {
concat!("Get atomic access to a `&mut ", stringify!($int_type), "`.
",
if_not_8_bit! {
$int_type,
concat!(
"**Note:** This function is only available on targets where `",
stringify!($int_type), "` has an alignment of ", $align, " bytes."
)
},
"
# Examples
```
#![feature(atomic_from_mut)]
", $extra_feature, "use std::sync::atomic::{", stringify!($atomic_type), ", Ordering};
let mut some_int = 123;
let a = ", stringify!($atomic_type), "::from_mut(&mut some_int);
a.store(100, Ordering::Relaxed);
assert_eq!(some_int, 100);
```
"),
#[inline]
$(#[cfg($from_mut_cfg)])?
#[unstable(feature = "atomic_from_mut", issue = "76314")]
pub fn from_mut(v: &mut $int_type) -> &Self {
let [] = [(); align_of::<Self>() - align_of::<$int_type>()];
// SAFETY:
// - the mutable reference guarantees unique ownership.
// - the alignment of `$int_type` and `Self` is the
// same on all platforms enabled by `$from_mut_cfg`
// as verified above.
unsafe { &*(v as *mut $int_type as *mut Self) }
}
}
doc_comment! {
concat!("Consumes the atomic and returns the contained value.
@ -1984,6 +2077,7 @@ atomic_int! {
stable(feature = "integer_atomics_stable", since = "1.34.0"),
rustc_const_stable(feature = "const_integer_atomics", since = "1.34.0"),
unstable(feature = "integer_atomics", issue = "32976"),
from_mut: cfg(not(target_arch = "x86")),
"i64", "../../../std/primitive.i64.html",
"",
atomic_min, atomic_max,
@ -2002,6 +2096,7 @@ atomic_int! {
stable(feature = "integer_atomics_stable", since = "1.34.0"),
rustc_const_stable(feature = "const_integer_atomics", since = "1.34.0"),
unstable(feature = "integer_atomics", issue = "32976"),
from_mut: cfg(not(target_arch = "x86")),
"u64", "../../../std/primitive.u64.html",
"",
atomic_umin, atomic_umax,
@ -2020,6 +2115,7 @@ atomic_int! {
unstable(feature = "integer_atomics", issue = "32976"),
rustc_const_stable(feature = "const_integer_atomics", since = "1.34.0"),
unstable(feature = "integer_atomics", issue = "32976"),
from_mut: cfg(not(target_arch = "x86_64")),
"i128", "../../../std/primitive.i128.html",
"#![feature(integer_atomics)]\n\n",
atomic_min, atomic_max,
@ -2038,6 +2134,7 @@ atomic_int! {
unstable(feature = "integer_atomics", issue = "32976"),
rustc_const_stable(feature = "const_integer_atomics", since = "1.34.0"),
unstable(feature = "integer_atomics", issue = "32976"),
from_mut: cfg(not(target_arch = "x86_64")),
"u128", "../../../std/primitive.u128.html",
"#![feature(integer_atomics)]\n\n",
atomic_umin, atomic_umax,