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Auto merge of #110861 - m-ou-se:thread-local-restructure, r=workingjubilee
Restructure and rename std thread_local internals to make it less of a maze Every time I try to work on std's thread local internals, it feels like I'm trying to navigate a confusing maze made of macros, deeply nested modules, and types with multiple names/aliases. Time to clean it up a bit. This PR: - Exports `Key` with its own name (`Key`), instead of `__LocalKeyInner` - Uses `pub macro` to put `__thread_local_inner` into a (unstable, hidden) module, removing `#[macro_export]`, removing it from the crate root. - Removes the `__` from `__thread_local_inner`. - Removes a few unnecessary `allow_internal_unstable` features from the macros - Removes the `libstd_thread_internals` feature. (Merged with `thread_local_internals`.) - And removes it from the unstable book - Gets rid of the deeply nested modules for the `Key` definitions (`mod fast` / `mod os` / `mod statik`). - Turns a `#[cfg]` mess into a single `cfg_if`, now that there's no `#[macro_export]` anymore that breaks with `cfg_if`. - Simplifies the `cfg_if` conditions to not repeat the conditions. - Removes useless `normalize-stderr-test`, which were left over from when the `Key` types had different names on different platforms. - Removes a seemingly unnecessary `realstd` re-export on `cfg(test)`. This PR changes nothing about the thread local implementation. That's for a later PR. (Which should hopefully be easier once all this stuff is a bit cleaned up.)
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‎library/std/src/sys/common/thread_local/fast_local.rs

+124-131
Original file line numberDiff line numberDiff line change
@@ -1,13 +1,14 @@
1+
use super::lazy::LazyKeyInner;
2+
use crate::cell::Cell;
3+
use crate::sys::thread_local_dtor::register_dtor;
4+
use crate::{fmt, mem, panic};
5+
16
#[doc(hidden)]
2-
#[macro_export]
3-
#[allow_internal_unstable(
4-
thread_local_internals,
5-
cfg_target_thread_local,
6-
thread_local,
7-
libstd_thread_internals
8-
)]
7+
#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)]
98
#[allow_internal_unsafe]
10-
macro_rules! __thread_local_inner {
9+
#[unstable(feature = "thread_local_internals", issue = "none")]
10+
#[rustc_macro_transparency = "semitransparent"]
11+
pub macro thread_local_inner {
1112
// used to generate the `LocalKey` value for const-initialized thread locals
1213
(@key $t:ty, const $init:expr) => {{
1314
#[cfg_attr(not(bootstrap), inline)]
@@ -49,7 +50,7 @@ macro_rules! __thread_local_inner {
4950
// 0 == we haven't registered a destructor, so do
5051
// so now.
5152
0 => {
52-
$crate::thread::__LocalKeyInner::<$t>::register_dtor(
53+
$crate::thread::local_impl::Key::<$t>::register_dtor(
5354
$crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8,
5455
destroy,
5556
);
@@ -69,7 +70,7 @@ macro_rules! __thread_local_inner {
6970
unsafe {
7071
$crate::thread::LocalKey::new(__getit)
7172
}
72-
}};
73+
}},
7374

7475
// used to generate the `LocalKey` value for `thread_local!`
7576
(@key $t:ty, $init:expr) => {
@@ -82,8 +83,8 @@ macro_rules! __thread_local_inner {
8283
init: $crate::option::Option<&mut $crate::option::Option<$t>>,
8384
) -> $crate::option::Option<&'static $t> {
8485
#[thread_local]
85-
static __KEY: $crate::thread::__LocalKeyInner<$t> =
86-
$crate::thread::__LocalKeyInner::<$t>::new();
86+
static __KEY: $crate::thread::local_impl::Key<$t> =
87+
$crate::thread::local_impl::Key::<$t>::new();
8788

8889
// FIXME: remove the #[allow(...)] marker when macros don't
8990
// raise warning for missing/extraneous unsafe blocks anymore.
@@ -107,148 +108,140 @@ macro_rules! __thread_local_inner {
107108
$crate::thread::LocalKey::new(__getit)
108109
}
109110
}
110-
};
111+
},
111112
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => {
112113
$(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
113-
$crate::__thread_local_inner!(@key $t, $($init)*);
114-
}
114+
$crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*);
115+
},
115116
}
116117

117-
#[doc(hidden)]
118-
pub mod fast {
119-
use super::super::lazy::LazyKeyInner;
120-
use crate::cell::Cell;
121-
use crate::sys::thread_local_dtor::register_dtor;
122-
use crate::{fmt, mem, panic};
123-
124-
#[derive(Copy, Clone)]
125-
enum DtorState {
126-
Unregistered,
127-
Registered,
128-
RunningOrHasRun,
129-
}
118+
#[derive(Copy, Clone)]
119+
enum DtorState {
120+
Unregistered,
121+
Registered,
122+
RunningOrHasRun,
123+
}
130124

131-
// This data structure has been carefully constructed so that the fast path
132-
// only contains one branch on x86. That optimization is necessary to avoid
133-
// duplicated tls lookups on OSX.
125+
// This data structure has been carefully constructed so that the fast path
126+
// only contains one branch on x86. That optimization is necessary to avoid
127+
// duplicated tls lookups on OSX.
128+
//
129+
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
130+
pub struct Key<T> {
131+
// If `LazyKeyInner::get` returns `None`, that indicates either:
132+
// * The value has never been initialized
133+
// * The value is being recursively initialized
134+
// * The value has already been destroyed or is being destroyed
135+
// To determine which kind of `None`, check `dtor_state`.
134136
//
135-
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
136-
pub struct Key<T> {
137-
// If `LazyKeyInner::get` returns `None`, that indicates either:
138-
// * The value has never been initialized
139-
// * The value is being recursively initialized
140-
// * The value has already been destroyed or is being destroyed
141-
// To determine which kind of `None`, check `dtor_state`.
142-
//
143-
// This is very optimizer friendly for the fast path - initialized but
144-
// not yet dropped.
145-
inner: LazyKeyInner<T>,
137+
// This is very optimizer friendly for the fast path - initialized but
138+
// not yet dropped.
139+
inner: LazyKeyInner<T>,
146140

147-
// Metadata to keep track of the state of the destructor. Remember that
148-
// this variable is thread-local, not global.
149-
dtor_state: Cell<DtorState>,
150-
}
141+
// Metadata to keep track of the state of the destructor. Remember that
142+
// this variable is thread-local, not global.
143+
dtor_state: Cell<DtorState>,
144+
}
151145

152-
impl<T> fmt::Debug for Key<T> {
153-
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
154-
f.debug_struct("Key").finish_non_exhaustive()
155-
}
146+
impl<T> fmt::Debug for Key<T> {
147+
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
148+
f.debug_struct("Key").finish_non_exhaustive()
156149
}
150+
}
157151

158-
impl<T> Key<T> {
159-
pub const fn new() -> Key<T> {
160-
Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) }
161-
}
152+
impl<T> Key<T> {
153+
pub const fn new() -> Key<T> {
154+
Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) }
155+
}
162156

163-
// note that this is just a publicly-callable function only for the
164-
// const-initialized form of thread locals, basically a way to call the
165-
// free `register_dtor` function defined elsewhere in std.
166-
pub unsafe fn register_dtor(a: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
167-
unsafe {
168-
register_dtor(a, dtor);
169-
}
157+
// note that this is just a publicly-callable function only for the
158+
// const-initialized form of thread locals, basically a way to call the
159+
// free `register_dtor` function defined elsewhere in std.
160+
pub unsafe fn register_dtor(a: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) {
161+
unsafe {
162+
register_dtor(a, dtor);
170163
}
164+
}
171165

172-
pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
173-
// SAFETY: See the definitions of `LazyKeyInner::get` and
174-
// `try_initialize` for more information.
175-
//
176-
// The caller must ensure no mutable references are ever active to
177-
// the inner cell or the inner T when this is called.
178-
// The `try_initialize` is dependant on the passed `init` function
179-
// for this.
180-
unsafe {
181-
match self.inner.get() {
182-
Some(val) => Some(val),
183-
None => self.try_initialize(init),
184-
}
166+
pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
167+
// SAFETY: See the definitions of `LazyKeyInner::get` and
168+
// `try_initialize` for more information.
169+
//
170+
// The caller must ensure no mutable references are ever active to
171+
// the inner cell or the inner T when this is called.
172+
// The `try_initialize` is dependant on the passed `init` function
173+
// for this.
174+
unsafe {
175+
match self.inner.get() {
176+
Some(val) => Some(val),
177+
None => self.try_initialize(init),
185178
}
186179
}
180+
}
187181

188-
// `try_initialize` is only called once per fast thread local variable,
189-
// except in corner cases where thread_local dtors reference other
190-
// thread_local's, or it is being recursively initialized.
191-
//
192-
// Macos: Inlining this function can cause two `tlv_get_addr` calls to
193-
// be performed for every call to `Key::get`.
194-
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
195-
#[inline(never)]
196-
unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
182+
// `try_initialize` is only called once per fast thread local variable,
183+
// except in corner cases where thread_local dtors reference other
184+
// thread_local's, or it is being recursively initialized.
185+
//
186+
// Macos: Inlining this function can cause two `tlv_get_addr` calls to
187+
// be performed for every call to `Key::get`.
188+
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
189+
#[inline(never)]
190+
unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
191+
// SAFETY: See comment above (this function doc).
192+
if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } {
197193
// SAFETY: See comment above (this function doc).
198-
if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } {
199-
// SAFETY: See comment above (this function doc).
200-
Some(unsafe { self.inner.initialize(init) })
201-
} else {
202-
None
203-
}
194+
Some(unsafe { self.inner.initialize(init) })
195+
} else {
196+
None
204197
}
198+
}
205199

206-
// `try_register_dtor` is only called once per fast thread local
207-
// variable, except in corner cases where thread_local dtors reference
208-
// other thread_local's, or it is being recursively initialized.
209-
unsafe fn try_register_dtor(&self) -> bool {
210-
match self.dtor_state.get() {
211-
DtorState::Unregistered => {
212-
// SAFETY: dtor registration happens before initialization.
213-
// Passing `self` as a pointer while using `destroy_value<T>`
214-
// is safe because the function will build a pointer to a
215-
// Key<T>, which is the type of self and so find the correct
216-
// size.
217-
unsafe { register_dtor(self as *const _ as *mut u8, destroy_value::<T>) };
218-
self.dtor_state.set(DtorState::Registered);
219-
true
220-
}
221-
DtorState::Registered => {
222-
// recursively initialized
223-
true
224-
}
225-
DtorState::RunningOrHasRun => false,
200+
// `try_register_dtor` is only called once per fast thread local
201+
// variable, except in corner cases where thread_local dtors reference
202+
// other thread_local's, or it is being recursively initialized.
203+
unsafe fn try_register_dtor(&self) -> bool {
204+
match self.dtor_state.get() {
205+
DtorState::Unregistered => {
206+
// SAFETY: dtor registration happens before initialization.
207+
// Passing `self` as a pointer while using `destroy_value<T>`
208+
// is safe because the function will build a pointer to a
209+
// Key<T>, which is the type of self and so find the correct
210+
// size.
211+
unsafe { register_dtor(self as *const _ as *mut u8, destroy_value::<T>) };
212+
self.dtor_state.set(DtorState::Registered);
213+
true
226214
}
215+
DtorState::Registered => {
216+
// recursively initialized
217+
true
218+
}
219+
DtorState::RunningOrHasRun => false,
227220
}
228221
}
222+
}
229223

230-
unsafe extern "C" fn destroy_value<T>(ptr: *mut u8) {
231-
let ptr = ptr as *mut Key<T>;
224+
unsafe extern "C" fn destroy_value<T>(ptr: *mut u8) {
225+
let ptr = ptr as *mut Key<T>;
232226

233-
// SAFETY:
234-
//
235-
// The pointer `ptr` has been built just above and comes from
236-
// `try_register_dtor` where it is originally a Key<T> coming from `self`,
237-
// making it non-NUL and of the correct type.
238-
//
239-
// Right before we run the user destructor be sure to set the
240-
// `Option<T>` to `None`, and `dtor_state` to `RunningOrHasRun`. This
241-
// causes future calls to `get` to run `try_initialize_drop` again,
242-
// which will now fail, and return `None`.
243-
//
244-
// Wrap the call in a catch to ensure unwinding is caught in the event
245-
// a panic takes place in a destructor.
246-
if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe {
247-
let value = (*ptr).inner.take();
248-
(*ptr).dtor_state.set(DtorState::RunningOrHasRun);
249-
drop(value);
250-
})) {
251-
rtabort!("thread local panicked on drop");
252-
}
227+
// SAFETY:
228+
//
229+
// The pointer `ptr` has been built just above and comes from
230+
// `try_register_dtor` where it is originally a Key<T> coming from `self`,
231+
// making it non-NUL and of the correct type.
232+
//
233+
// Right before we run the user destructor be sure to set the
234+
// `Option<T>` to `None`, and `dtor_state` to `RunningOrHasRun`. This
235+
// causes future calls to `get` to run `try_initialize_drop` again,
236+
// which will now fail, and return `None`.
237+
//
238+
// Wrap the call in a catch to ensure unwinding is caught in the event
239+
// a panic takes place in a destructor.
240+
if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe {
241+
let value = (*ptr).inner.take();
242+
(*ptr).dtor_state.set(DtorState::RunningOrHasRun);
243+
drop(value);
244+
})) {
245+
rtabort!("thread local panicked on drop");
253246
}
254247
}

‎library/std/src/sys/common/thread_local/mod.rs

+11-22
Original file line numberDiff line numberDiff line change
@@ -1,35 +1,24 @@
1-
//! The following module declarations are outside cfg_if because the internal
2-
//! `__thread_local_internal` macro does not seem to be exported properly when using cfg_if
31
#![unstable(feature = "thread_local_internals", reason = "should not be necessary", issue = "none")]
42

5-
#[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics")))))]
6-
mod fast_local;
7-
#[cfg(all(
8-
not(target_thread_local),
9-
not(all(target_family = "wasm", not(target_feature = "atomics")))
10-
))]
11-
mod os_local;
12-
#[cfg(all(target_family = "wasm", not(target_feature = "atomics")))]
13-
mod static_local;
14-
15-
#[cfg(not(test))]
163
cfg_if::cfg_if! {
174
if #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] {
185
#[doc(hidden)]
19-
pub use static_local::statik::Key;
20-
} else if #[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics")))))] {
6+
mod static_local;
7+
#[doc(hidden)]
8+
pub use static_local::{Key, thread_local_inner};
9+
} else if #[cfg(all(target_thread_local))] {
10+
#[doc(hidden)]
11+
mod fast_local;
2112
#[doc(hidden)]
22-
pub use fast_local::fast::Key;
23-
} else if #[cfg(all(not(target_thread_local), not(all(target_family = "wasm", not(target_feature = "atomics")))))] {
13+
pub use fast_local::{Key, thread_local_inner};
14+
} else {
2415
#[doc(hidden)]
25-
pub use os_local::os::Key;
16+
mod os_local;
17+
#[doc(hidden)]
18+
pub use os_local::{Key, thread_local_inner};
2619
}
2720
}
2821

29-
#[doc(hidden)]
30-
#[cfg(test)]
31-
pub use realstd::thread::__LocalKeyInner as Key;
32-
3322
mod lazy {
3423
use crate::cell::UnsafeCell;
3524
use crate::hint;

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