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mv std libs to library/

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2020-06-11 21:31:49 -05:00
parent 9be8ffcb02
commit 2c31b45ae8
875 changed files with 1255 additions and 1223 deletions
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library/std/src/thread/local.rs Normal file
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//! Thread local storage
#![unstable(feature = "thread_local_internals", issue = "none")]
use crate::error::Error;
use crate::fmt;
/// A thread local storage key which owns its contents.
///
/// This key uses the fastest possible implementation available to it for the
/// target platform. It is instantiated with the [`thread_local!`] macro and the
/// primary method is the [`with`] method.
///
/// The [`with`] method yields a reference to the contained value which cannot be
/// sent across threads or escape the given closure.
///
/// # Initialization and Destruction
///
/// Initialization is dynamically performed on the first call to [`with`]
/// within a thread, and values that implement [`Drop`] get destructed when a
/// thread exits. Some caveats apply, which are explained below.
///
/// A `LocalKey`'s initializer cannot recursively depend on itself, and using
/// a `LocalKey` in this way will cause the initializer to infinitely recurse
/// on the first call to `with`.
///
/// # Examples
///
/// ```
/// use std::cell::RefCell;
/// use std::thread;
///
/// thread_local!(static FOO: RefCell<u32> = RefCell::new(1));
///
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 1);
/// *f.borrow_mut() = 2;
/// });
///
/// // each thread starts out with the initial value of 1
/// let t = thread::spawn(move|| {
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 1);
/// *f.borrow_mut() = 3;
/// });
/// });
///
/// // wait for the thread to complete and bail out on panic
/// t.join().unwrap();
///
/// // we retain our original value of 2 despite the child thread
/// FOO.with(|f| {
/// assert_eq!(*f.borrow(), 2);
/// });
/// ```
///
/// # Platform-specific behavior
///
/// Note that a "best effort" is made to ensure that destructors for types
/// stored in thread local storage are run, but not all platforms can guarantee
/// that destructors will be run for all types in thread local storage. For
/// example, there are a number of known caveats where destructors are not run:
///
/// 1. On Unix systems when pthread-based TLS is being used, destructors will
/// not be run for TLS values on the main thread when it exits. Note that the
/// application will exit immediately after the main thread exits as well.
/// 2. On all platforms it's possible for TLS to re-initialize other TLS slots
/// during destruction. Some platforms ensure that this cannot happen
/// infinitely by preventing re-initialization of any slot that has been
/// destroyed, but not all platforms have this guard. Those platforms that do
/// not guard typically have a synthetic limit after which point no more
/// destructors are run.
///
/// [`with`]: ../../std/thread/struct.LocalKey.html#method.with
/// [`thread_local!`]: ../../std/macro.thread_local.html
/// [`Drop`]: ../../std/ops/trait.Drop.html
#[stable(feature = "rust1", since = "1.0.0")]
pub struct LocalKey<T: 'static> {
// This outer `LocalKey<T>` type is what's going to be stored in statics,
// but actual data inside will sometimes be tagged with #[thread_local].
// It's not valid for a true static to reference a #[thread_local] static,
// so we get around that by exposing an accessor through a layer of function
// indirection (this thunk).
//
// Note that the thunk is itself unsafe because the returned lifetime of the
// slot where data lives, `'static`, is not actually valid. The lifetime
// here is actually slightly shorter than the currently running thread!
//
// Although this is an extra layer of indirection, it should in theory be
// trivially devirtualizable by LLVM because the value of `inner` never
// changes and the constant should be readonly within a crate. This mainly
// only runs into problems when TLS statics are exported across crates.
inner: unsafe fn() -> Option<&'static T>,
}
#[stable(feature = "std_debug", since = "1.16.0")]
impl<T: 'static> fmt::Debug for LocalKey<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("LocalKey { .. }")
}
}
/// Declare a new thread local storage key of type [`std::thread::LocalKey`].
///
/// # Syntax
///
/// The macro wraps any number of static declarations and makes them thread local.
/// Publicity and attributes for each static are allowed. Example:
///
/// ```
/// use std::cell::RefCell;
/// thread_local! {
/// pub static FOO: RefCell<u32> = RefCell::new(1);
///
/// #[allow(unused)]
/// static BAR: RefCell<f32> = RefCell::new(1.0);
/// }
/// # fn main() {}
/// ```
///
/// See [LocalKey documentation][`std::thread::LocalKey`] for more
/// information.
///
/// [`std::thread::LocalKey`]: ../std/thread/struct.LocalKey.html
#[macro_export]
#[stable(feature = "rust1", since = "1.0.0")]
#[allow_internal_unstable(thread_local_internals)]
macro_rules! thread_local {
// empty (base case for the recursion)
() => {};
// process multiple declarations
($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => (
$crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
$crate::thread_local!($($rest)*);
);
// handle a single declaration
($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr) => (
$crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, $init);
);
}
#[doc(hidden)]
#[unstable(feature = "thread_local_internals", reason = "should not be necessary", issue = "none")]
#[macro_export]
#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)]
#[allow_internal_unsafe]
macro_rules! __thread_local_inner {
(@key $t:ty, $init:expr) => {
{
#[inline]
fn __init() -> $t { $init }
unsafe fn __getit() -> $crate::option::Option<&'static $t> {
#[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))]
static __KEY: $crate::thread::__StaticLocalKeyInner<$t> =
$crate::thread::__StaticLocalKeyInner::new();
#[thread_local]
#[cfg(all(
target_thread_local,
not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
))]
static __KEY: $crate::thread::__FastLocalKeyInner<$t> =
$crate::thread::__FastLocalKeyInner::new();
#[cfg(all(
not(target_thread_local),
not(all(target_arch = "wasm32", not(target_feature = "atomics"))),
))]
static __KEY: $crate::thread::__OsLocalKeyInner<$t> =
$crate::thread::__OsLocalKeyInner::new();
__KEY.get(__init)
}
unsafe {
$crate::thread::LocalKey::new(__getit)
}
}
};
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $init:expr) => {
$(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> =
$crate::__thread_local_inner!(@key $t, $init);
}
}
/// An error returned by [`LocalKey::try_with`](struct.LocalKey.html#method.try_with).
#[stable(feature = "thread_local_try_with", since = "1.26.0")]
#[derive(Clone, Copy, Eq, PartialEq)]
pub struct AccessError {
_private: (),
}
#[stable(feature = "thread_local_try_with", since = "1.26.0")]
impl fmt::Debug for AccessError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("AccessError").finish()
}
}
#[stable(feature = "thread_local_try_with", since = "1.26.0")]
impl fmt::Display for AccessError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt::Display::fmt("already destroyed", f)
}
}
#[stable(feature = "thread_local_try_with", since = "1.26.0")]
impl Error for AccessError {}
impl<T: 'static> LocalKey<T> {
#[doc(hidden)]
#[unstable(
feature = "thread_local_internals",
reason = "recently added to create a key",
issue = "none"
)]
pub const unsafe fn new(inner: unsafe fn() -> Option<&'static T>) -> LocalKey<T> {
LocalKey { inner }
}
/// Acquires a reference to the value in this TLS key.
///
/// This will lazily initialize the value if this thread has not referenced
/// this key yet.
///
/// # Panics
///
/// This function will `panic!()` if the key currently has its
/// destructor running, and it **may** panic if the destructor has
/// previously been run for this thread.
#[stable(feature = "rust1", since = "1.0.0")]
pub fn with<F, R>(&'static self, f: F) -> R
where
F: FnOnce(&T) -> R,
{
self.try_with(f).expect(
"cannot access a Thread Local Storage value \
during or after destruction",
)
}
/// Acquires a reference to the value in this TLS key.
///
/// This will lazily initialize the value if this thread has not referenced
/// this key yet. If the key has been destroyed (which may happen if this is called
/// in a destructor), this function will return an [`AccessError`](struct.AccessError.html).
///
/// # Panics
///
/// This function will still `panic!()` if the key is uninitialized and the
/// key's initializer panics.
#[stable(feature = "thread_local_try_with", since = "1.26.0")]
#[inline]
pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError>
where
F: FnOnce(&T) -> R,
{
unsafe {
let thread_local = (self.inner)().ok_or(AccessError { _private: () })?;
Ok(f(thread_local))
}
}
}
mod lazy {
use crate::cell::UnsafeCell;
use crate::hint;
use crate::mem;
pub struct LazyKeyInner<T> {
inner: UnsafeCell<Option<T>>,
}
impl<T> LazyKeyInner<T> {
pub const fn new() -> LazyKeyInner<T> {
LazyKeyInner { inner: UnsafeCell::new(None) }
}
pub unsafe fn get(&self) -> Option<&'static T> {
(*self.inner.get()).as_ref()
}
pub unsafe fn initialize<F: FnOnce() -> T>(&self, init: F) -> &'static T {
// Execute the initialization up front, *then* move it into our slot,
// just in case initialization fails.
let value = init();
let ptr = self.inner.get();
// note that this can in theory just be `*ptr = Some(value)`, but due to
// the compiler will currently codegen that pattern with something like:
//
// ptr::drop_in_place(ptr)
// ptr::write(ptr, Some(value))
//
// Due to this pattern it's possible for the destructor of the value in
// `ptr` (e.g., if this is being recursively initialized) to re-access
// TLS, in which case there will be a `&` and `&mut` pointer to the same
// value (an aliasing violation). To avoid setting the "I'm running a
// destructor" flag we just use `mem::replace` which should sequence the
// operations a little differently and make this safe to call.
let _ = mem::replace(&mut *ptr, Some(value));
// After storing `Some` we want to get a reference to the contents of
// what we just stored. While we could use `unwrap` here and it should
// always work it empirically doesn't seem to always get optimized away,
// which means that using something like `try_with` can pull in
// panicking code and cause a large size bloat.
match *ptr {
Some(ref x) => x,
None => hint::unreachable_unchecked(),
}
}
#[allow(unused)]
pub unsafe fn take(&mut self) -> Option<T> {
(*self.inner.get()).take()
}
}
}
/// On some platforms like wasm32 there's no threads, so no need to generate
/// thread locals and we can instead just use plain statics!
#[doc(hidden)]
#[cfg(all(target_arch = "wasm32", not(target_feature = "atomics")))]
pub mod statik {
use super::lazy::LazyKeyInner;
use crate::fmt;
pub struct Key<T> {
inner: LazyKeyInner<T>,
}
unsafe impl<T> Sync for Key<T> {}
impl<T> fmt::Debug for Key<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Key { .. }")
}
}
impl<T> Key<T> {
pub const fn new() -> Key<T> {
Key { inner: LazyKeyInner::new() }
}
pub unsafe fn get(&self, init: fn() -> T) -> Option<&'static T> {
let value = match self.inner.get() {
Some(ref value) => value,
None => self.inner.initialize(init),
};
Some(value)
}
}
}
#[doc(hidden)]
#[cfg(target_thread_local)]
pub mod fast {
use super::lazy::LazyKeyInner;
use crate::cell::Cell;
use crate::fmt;
use crate::mem;
use crate::sys::thread_local_dtor::register_dtor;
#[derive(Copy, Clone)]
enum DtorState {
Unregistered,
Registered,
RunningOrHasRun,
}
// This data structure has been carefully constructed so that the fast path
// only contains one branch on x86. That optimization is necessary to avoid
// duplicated tls lookups on OSX.
//
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
pub struct Key<T> {
// If `LazyKeyInner::get` returns `None`, that indicates either:
// * The value has never been initialized
// * The value is being recursively initialized
// * The value has already been destroyed or is being destroyed
// To determine which kind of `None`, check `dtor_state`.
//
// This is very optimizer friendly for the fast path - initialized but
// not yet dropped.
inner: LazyKeyInner<T>,
// Metadata to keep track of the state of the destructor. Remember that
// this variable is thread-local, not global.
dtor_state: Cell<DtorState>,
}
impl<T> fmt::Debug for Key<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Key { .. }")
}
}
impl<T> Key<T> {
pub const fn new() -> Key<T> {
Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) }
}
pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
match self.inner.get() {
Some(val) => Some(val),
None => self.try_initialize(init),
}
}
// `try_initialize` is only called once per fast thread local variable,
// except in corner cases where thread_local dtors reference other
// thread_local's, or it is being recursively initialized.
//
// Macos: Inlining this function can cause two `tlv_get_addr` calls to
// be performed for every call to `Key::get`. The #[cold] hint makes
// that less likely.
// LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722
#[cold]
unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> {
if !mem::needs_drop::<T>() || self.try_register_dtor() {
Some(self.inner.initialize(init))
} else {
None
}
}
// `try_register_dtor` is only called once per fast thread local
// variable, except in corner cases where thread_local dtors reference
// other thread_local's, or it is being recursively initialized.
unsafe fn try_register_dtor(&self) -> bool {
match self.dtor_state.get() {
DtorState::Unregistered => {
// dtor registration happens before initialization.
register_dtor(self as *const _ as *mut u8, destroy_value::<T>);
self.dtor_state.set(DtorState::Registered);
true
}
DtorState::Registered => {
// recursively initialized
true
}
DtorState::RunningOrHasRun => false,
}
}
}
unsafe extern "C" fn destroy_value<T>(ptr: *mut u8) {
let ptr = ptr as *mut Key<T>;
// Right before we run the user destructor be sure to set the
// `Option<T>` to `None`, and `dtor_state` to `RunningOrHasRun`. This
// causes future calls to `get` to run `try_initialize_drop` again,
// which will now fail, and return `None`.
let value = (*ptr).inner.take();
(*ptr).dtor_state.set(DtorState::RunningOrHasRun);
drop(value);
}
}
#[doc(hidden)]
pub mod os {
use super::lazy::LazyKeyInner;
use crate::cell::Cell;
use crate::fmt;
use crate::marker;
use crate::ptr;
use crate::sys_common::thread_local_key::StaticKey as OsStaticKey;
pub struct Key<T> {
// OS-TLS key that we'll use to key off.
os: OsStaticKey,
marker: marker::PhantomData<Cell<T>>,
}
impl<T> fmt::Debug for Key<T> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.pad("Key { .. }")
}
}
unsafe impl<T> Sync for Key<T> {}
struct Value<T: 'static> {
inner: LazyKeyInner<T>,
key: &'static Key<T>,
}
impl<T: 'static> Key<T> {
pub const fn new() -> Key<T> {
Key { os: OsStaticKey::new(Some(destroy_value::<T>)), marker: marker::PhantomData }
}
pub unsafe fn get(&'static self, init: fn() -> T) -> Option<&'static T> {
let ptr = self.os.get() as *mut Value<T>;
if ptr as usize > 1 {
if let Some(ref value) = (*ptr).inner.get() {
return Some(value);
}
}
self.try_initialize(init)
}
// `try_initialize` is only called once per os thread local variable,
// except in corner cases where thread_local dtors reference other
// thread_local's, or it is being recursively initialized.
unsafe fn try_initialize(&'static self, init: fn() -> T) -> Option<&'static T> {
let ptr = self.os.get() as *mut Value<T>;
if ptr as usize == 1 {
// destructor is running
return None;
}
let ptr = if ptr.is_null() {
// If the lookup returned null, we haven't initialized our own
// local copy, so do that now.
let ptr: Box<Value<T>> = box Value { inner: LazyKeyInner::new(), key: self };
let ptr = Box::into_raw(ptr);
self.os.set(ptr as *mut u8);
ptr
} else {
// recursive initialization
ptr
};
Some((*ptr).inner.initialize(init))
}
}
unsafe extern "C" fn destroy_value<T: 'static>(ptr: *mut u8) {
// The OS TLS ensures that this key contains a NULL value when this
// destructor starts to run. We set it back to a sentinel value of 1 to
// ensure that any future calls to `get` for this thread will return
// `None`.
//
// Note that to prevent an infinite loop we reset it back to null right
// before we return from the destructor ourselves.
let ptr = Box::from_raw(ptr as *mut Value<T>);
let key = ptr.key;
key.os.set(1 as *mut u8);
drop(ptr);
key.os.set(ptr::null_mut());
}
}
#[cfg(all(test, not(target_os = "emscripten")))]
mod tests {
use crate::cell::{Cell, UnsafeCell};
use crate::sync::mpsc::{channel, Sender};
use crate::thread;
struct Foo(Sender<()>);
impl Drop for Foo {
fn drop(&mut self) {
let Foo(ref s) = *self;
s.send(()).unwrap();
}
}
#[test]
fn smoke_no_dtor() {
thread_local!(static FOO: Cell<i32> = Cell::new(1));
FOO.with(|f| {
assert_eq!(f.get(), 1);
f.set(2);
});
let (tx, rx) = channel();
let _t = thread::spawn(move || {
FOO.with(|f| {
assert_eq!(f.get(), 1);
});
tx.send(()).unwrap();
});
rx.recv().unwrap();
FOO.with(|f| {
assert_eq!(f.get(), 2);
});
}
#[test]
fn states() {
struct Foo;
impl Drop for Foo {
fn drop(&mut self) {
assert!(FOO.try_with(|_| ()).is_err());
}
}
thread_local!(static FOO: Foo = Foo);
thread::spawn(|| {
assert!(FOO.try_with(|_| ()).is_ok());
})
.join()
.ok()
.expect("thread panicked");
}
#[test]
fn smoke_dtor() {
thread_local!(static FOO: UnsafeCell<Option<Foo>> = UnsafeCell::new(None));
let (tx, rx) = channel();
let _t = thread::spawn(move || unsafe {
let mut tx = Some(tx);
FOO.with(|f| {
*f.get() = Some(Foo(tx.take().unwrap()));
});
});
rx.recv().unwrap();
}
#[test]
fn circular() {
struct S1;
struct S2;
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
thread_local!(static K2: UnsafeCell<Option<S2>> = UnsafeCell::new(None));
static mut HITS: u32 = 0;
impl Drop for S1 {
fn drop(&mut self) {
unsafe {
HITS += 1;
if K2.try_with(|_| ()).is_err() {
assert_eq!(HITS, 3);
} else {
if HITS == 1 {
K2.with(|s| *s.get() = Some(S2));
} else {
assert_eq!(HITS, 3);
}
}
}
}
}
impl Drop for S2 {
fn drop(&mut self) {
unsafe {
HITS += 1;
assert!(K1.try_with(|_| ()).is_ok());
assert_eq!(HITS, 2);
K1.with(|s| *s.get() = Some(S1));
}
}
}
thread::spawn(move || {
drop(S1);
})
.join()
.ok()
.expect("thread panicked");
}
#[test]
fn self_referential() {
struct S1;
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
impl Drop for S1 {
fn drop(&mut self) {
assert!(K1.try_with(|_| ()).is_err());
}
}
thread::spawn(move || unsafe {
K1.with(|s| *s.get() = Some(S1));
})
.join()
.ok()
.expect("thread panicked");
}
// Note that this test will deadlock if TLS destructors aren't run (this
// requires the destructor to be run to pass the test).
#[test]
fn dtors_in_dtors_in_dtors() {
struct S1(Sender<()>);
thread_local!(static K1: UnsafeCell<Option<S1>> = UnsafeCell::new(None));
thread_local!(static K2: UnsafeCell<Option<Foo>> = UnsafeCell::new(None));
impl Drop for S1 {
fn drop(&mut self) {
let S1(ref tx) = *self;
unsafe {
let _ = K2.try_with(|s| *s.get() = Some(Foo(tx.clone())));
}
}
}
let (tx, rx) = channel();
let _t = thread::spawn(move || unsafe {
let mut tx = Some(tx);
K1.with(|s| *s.get() = Some(S1(tx.take().unwrap())));
});
rx.recv().unwrap();
}
}
#[cfg(test)]
mod dynamic_tests {
use crate::cell::RefCell;
use crate::collections::HashMap;
#[test]
fn smoke() {
fn square(i: i32) -> i32 {
i * i
}
thread_local!(static FOO: i32 = square(3));
FOO.with(|f| {
assert_eq!(*f, 9);
});
}
#[test]
fn hashmap() {
fn map() -> RefCell<HashMap<i32, i32>> {
let mut m = HashMap::new();
m.insert(1, 2);
RefCell::new(m)
}
thread_local!(static FOO: RefCell<HashMap<i32, i32>> = map());
FOO.with(|map| {
assert_eq!(map.borrow()[&1], 2);
});
}
#[test]
fn refcell_vec() {
thread_local!(static FOO: RefCell<Vec<u32>> = RefCell::new(vec![1, 2, 3]));
FOO.with(|vec| {
assert_eq!(vec.borrow().len(), 3);
vec.borrow_mut().push(4);
assert_eq!(vec.borrow()[3], 4);
});
}
}

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