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Support #[rustc_align_static] inside thread_local! #146281

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4 changes: 3 additions & 1 deletion library/std/src/sys/thread_local/native/eager.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -10,9 +10,11 @@ enum State {
}

#[allow(missing_debug_implementations)]
#[repr(C)]
pub struct Storage<T> {
state:Cell<State>,
// This field must be first, for correctness of `#[rustc_align_static]`
val: UnsafeCell<T>,
state: Cell<State>,
}

impl<T> Storage<T> {
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4 changes: 3 additions & 1 deletion library/std/src/sys/thread_local/native/lazy.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -27,9 +27,11 @@ enum State<D> {
}

#[allow(missing_debug_implementations)]
#[repr(C)]
pub struct Storage<T, D> {
state: Cell<State<D>>,
// This field must be first, for correctness of `#[rustc_align_static]`
value: UnsafeCell<MaybeUninit<T>>,
state: Cell<State<D>>,
}

impl<T, D> Storage<T, D>
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12 changes: 8 additions & 4 deletions library/std/src/sys/thread_local/native/mod.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -54,21 +54,23 @@ pub macro thread_local_inner {
// test in `tests/thread.rs` if these types are renamed.

// Used to generate the `LocalKey` value for const-initialized thread locals.
(@key $t:ty, const $init:expr) => {{
(@key $t:ty, $(#[$align_attr:meta])*, const $init:expr) => {{
const __INIT: $t = $init;

unsafe {
$crate::thread::LocalKey::new(const {
if $crate::mem::needs_drop::<$t>() {
|_| {
#[thread_local]
$(#[$align_attr])*
static VAL: $crate::thread::local_impl::EagerStorage<$t>
= $crate::thread::local_impl::EagerStorage::new(__INIT);
VAL.get()
}
} else {
|_| {
#[thread_local]
$(#[$align_attr])*
static VAL: $t = __INIT;
&VAL
}
Expand All @@ -78,7 +80,7 @@ pub macro thread_local_inner {
}},

// used to generate the `LocalKey` value for `thread_local!`
(@key $t:ty, $init:expr) => {{
(@key $t:ty, $(#[$align_attr:meta])*, $init:expr) => {{
#[inline]
fn __init() -> $t {
$init
Expand All @@ -89,13 +91,15 @@ pub macro thread_local_inner {
if $crate::mem::needs_drop::<$t>() {
|init| {
#[thread_local]
$(#[$align_attr])*
static VAL: $crate::thread::local_impl::LazyStorage<$t, ()>
= $crate::thread::local_impl::LazyStorage::new();
VAL.get_or_init(init, __init)
}
} else {
|init| {
#[thread_local]
$(#[$align_attr])*
static VAL: $crate::thread::local_impl::LazyStorage<$t, !>
= $crate::thread::local_impl::LazyStorage::new();
VAL.get_or_init(init, __init)
Expand All @@ -104,9 +108,9 @@ pub macro thread_local_inner {
})
}
}},
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $(#[$align_attr:meta])*, $($init:tt)*) => {
$(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
$crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*);
$crate::thread::local_impl::thread_local_inner!(@key $t, $(#[$align_attr])*, $($init)*);
},
}

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62 changes: 47 additions & 15 deletions library/std/src/sys/thread_local/no_threads.rs
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
//! thread locals and we can instead just use plain statics!

use crate::cell::{Cell, UnsafeCell};
use crate::mem::MaybeUninit;
use crate::ptr;

#[doc(hidden)]
Expand All @@ -11,12 +12,13 @@ use crate::ptr;
#[rustc_macro_transparency = "semitransparent"]
pub macro thread_local_inner {
// used to generate the `LocalKey` value for const-initialized thread locals
(@key $t:ty, const $init:expr) => {{
(@key $t:ty, $(#[$align_attr:meta])*, const $init:expr) => {{
const __INIT: $t = $init;

// NOTE: Please update the shadowing test in `tests/thread.rs` if these types are renamed.
unsafe {
$crate::thread::LocalKey::new(|_| {
$(#[$align_attr])*
static VAL: $crate::thread::local_impl::EagerStorage<$t> =
$crate::thread::local_impl::EagerStorage { value: __INIT };
&VAL.value
Expand All @@ -25,7 +27,7 @@ pub macro thread_local_inner {
}},

// used to generate the `LocalKey` value for `thread_local!`
(@key $t:ty, $init:expr) => {{
(@key $t:ty, $(#[$align_attr:meta])*, $init:expr) => {{
#[inline]
fn __init() -> $t { $init }

Expand All @@ -34,33 +36,48 @@ pub macro thread_local_inner {
use $crate::thread::local_impl::LazyStorage;

LocalKey::new(|init| {
$(#[$align_attr])*
static VAL: LazyStorage<$t> = LazyStorage::new();
VAL.get(init, __init)
})
}
}},
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $(#[$align_attr:meta])*, $($init:tt)*) => {
$(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
$crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*);
$crate::thread::local_impl::thread_local_inner!(@key $t, $(#[$align_attr])*, $($init)*);
},
}

#[allow(missing_debug_implementations)]
#[repr(transparent)] // Required for correctness of `#[rustc_align_static]`
pub struct EagerStorage<T> {
pub value: T,
}

// SAFETY: the target doesn't have threads.
unsafe impl<T> Sync for EagerStorage<T> {}

#[derive(Clone, Copy, PartialEq, Eq)]
enum State {
Initial,
Alive,
Destroying,
}

#[allow(missing_debug_implementations)]
#[repr(C)]
pub struct LazyStorage<T> {
value: UnsafeCell<Option<T>>,
// This field must be first, for correctness of `#[rustc_align_static]`
value: UnsafeCell<MaybeUninit<T>>,
state: Cell<State>,
}

impl<T> LazyStorage<T> {
pub const fn new() -> LazyStorage<T> {
LazyStorage { value: UnsafeCell::new(None) }
LazyStorage {
value: UnsafeCell::new(MaybeUninit::uninit()),
state: Cell::new(State::Initial),
}
}

/// Gets a pointer to the TLS value, potentially initializing it with the
Expand All @@ -70,24 +87,39 @@ impl<T> LazyStorage<T> {
/// has occurred.
#[inline]
pub fn get(&'static self, i: Option<&mut Option<T>>, f: impl FnOnce() -> T) -> *const T {
let value = unsafe { &*self.value.get() };
match value {
Some(v) => v,
None => self.initialize(i, f),
if self.state.get() == State::Alive {
self.value.get() as *const T
} else {
self.initialize(i, f)
}
}

#[cold]
fn initialize(&'static self, i: Option<&mut Option<T>>, f: impl FnOnce() -> T) -> *const T {
let value = i.and_then(Option::take).unwrap_or_else(f);
// Destroy the old value, after updating the TLS variable as the
// destructor might reference it.

// Destroy the old value if it is initialized
// FIXME(#110897): maybe panic on recursive initialization.
if self.state.get() == State::Alive {
self.state.set(State::Destroying);
// Safety: we check for no initialization during drop below
unsafe {
ptr::drop_in_place(self.value.get() as *mut T);
}
self.state.set(State::Initial);
}

// Guard against initialization during drop
if self.state.get() == State::Destroying {
panic!("Attempted to initialize thread-local while it is being dropped");
}

unsafe {
self.value.get().replace(Some(value));
self.value.get().write(MaybeUninit::new(value));
}
// SAFETY: we just set this to `Some`.
unsafe { (*self.value.get()).as_ref().unwrap_unchecked() }
self.state.set(State::Alive);

self.value.get() as *const T
}
}

Expand Down
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