diff options
Diffstat (limited to 'library/std/src/sys/thread_local')
| -rw-r--r-- | library/std/src/sys/thread_local/fast_local.rs | 247 | ||||
| -rw-r--r-- | library/std/src/sys/thread_local/mod.rs | 124 | ||||
| -rw-r--r-- | library/std/src/sys/thread_local/os_local.rs | 185 | ||||
| -rw-r--r-- | library/std/src/sys/thread_local/static_local.rs | 108 |
4 files changed, 664 insertions, 0 deletions
diff --git a/library/std/src/sys/thread_local/fast_local.rs b/library/std/src/sys/thread_local/fast_local.rs new file mode 100644 index 00000000000..646dcd7f3a3 --- /dev/null +++ b/library/std/src/sys/thread_local/fast_local.rs @@ -0,0 +1,247 @@ +use super::lazy::LazyKeyInner; +use crate::cell::Cell; +use crate::sys::thread_local_dtor::register_dtor; +use crate::{fmt, mem, panic}; + +#[doc(hidden)] +#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)] +#[allow_internal_unsafe] +#[unstable(feature = "thread_local_internals", issue = "none")] +#[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) => {{ + #[inline] + #[deny(unsafe_op_in_unsafe_fn)] + // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint + #[cfg_attr(bootstrap, allow(static_mut_ref))] + #[cfg_attr(not(bootstrap), allow(static_mut_refs))] + unsafe fn __getit( + _init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + const INIT_EXPR: $t = $init; + // If the platform has support for `#[thread_local]`, use it. + #[thread_local] + static mut VAL: $t = INIT_EXPR; + + // If a dtor isn't needed we can do something "very raw" and + // just get going. + if !$crate::mem::needs_drop::<$t>() { + unsafe { + return $crate::option::Option::Some(&VAL) + } + } + + // 0 == dtor not registered + // 1 == dtor registered, dtor not run + // 2 == dtor registered and is running or has run + #[thread_local] + static STATE: $crate::cell::Cell<$crate::primitive::u8> = $crate::cell::Cell::new(0); + + // Safety: Performs `drop_in_place(ptr as *mut $t)`, and requires + // all that comes with it. + unsafe extern "C" fn destroy(ptr: *mut $crate::primitive::u8) { + $crate::thread::local_impl::abort_on_dtor_unwind(|| { + let old_state = STATE.replace(2); + $crate::debug_assert_eq!(old_state, 1); + // Safety: safety requirement is passed on to caller. + unsafe { $crate::ptr::drop_in_place(ptr.cast::<$t>()); } + }); + } + + unsafe { + match STATE.get() { + // 0 == we haven't registered a destructor, so do + // so now. + 0 => { + $crate::thread::local_impl::Key::<$t>::register_dtor( + $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8, + destroy, + ); + STATE.set(1); + $crate::option::Option::Some(&VAL) + } + // 1 == the destructor is registered and the value + // is valid, so return the pointer. + 1 => $crate::option::Option::Some(&VAL), + // otherwise the destructor has already run, so we + // can't give access. + _ => $crate::option::Option::None, + } + } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + }}, + + // used to generate the `LocalKey` value for `thread_local!` + (@key $t:ty, $init:expr) => { + { + #[inline] + fn __init() -> $t { $init } + + #[inline] + unsafe fn __getit( + init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + #[thread_local] + static __KEY: $crate::thread::local_impl::Key<$t> = + $crate::thread::local_impl::Key::<$t>::new(); + + unsafe { + __KEY.get(move || { + if let $crate::option::Option::Some(init) = init { + if let $crate::option::Option::Some(value) = init.take() { + return value; + } + if $crate::cfg!(debug_assertions) { + $crate::unreachable!("missing default value"); + } + } + __init() + }) + } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + } + }, + ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => { + $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> = + $crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*); + }, +} + +#[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.debug_struct("Key").finish_non_exhaustive() + } +} +impl<T> Key<T> { + pub const fn new() -> Key<T> { + Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) } + } + + // note that this is just a publicly-callable function only for the + // const-initialized form of thread locals, basically a way to call the + // free `register_dtor` function defined elsewhere in std. + pub unsafe fn register_dtor(a: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) { + unsafe { + register_dtor(a, dtor); + } + } + + pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> { + // SAFETY: See the definitions of `LazyKeyInner::get` and + // `try_initialize` for more information. + // + // The caller must ensure no mutable references are ever active to + // the inner cell or the inner T when this is called. + // The `try_initialize` is dependant on the passed `init` function + // for this. + unsafe { + 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`. + // LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722 + #[inline(never)] + unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> { + // SAFETY: See comment above (this function doc). + if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } { + // SAFETY: See comment above (this function doc). + Some(unsafe { 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 => { + // SAFETY: dtor registration happens before initialization. + // Passing `self` as a pointer while using `destroy_value<T>` + // is safe because the function will build a pointer to a + // Key<T>, which is the type of self and so find the correct + // size. + unsafe { 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>; + + // SAFETY: + // + // The pointer `ptr` has been built just above and comes from + // `try_register_dtor` where it is originally a Key<T> coming from `self`, + // making it non-NUL and of the correct type. + // + // 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`. + // + // Wrap the call in a catch to ensure unwinding is caught in the event + // a panic takes place in a destructor. + if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe { + let value = (*ptr).inner.take(); + (*ptr).dtor_state.set(DtorState::RunningOrHasRun); + drop(value); + })) { + rtabort!("thread local panicked on drop"); + } +} diff --git a/library/std/src/sys/thread_local/mod.rs b/library/std/src/sys/thread_local/mod.rs new file mode 100644 index 00000000000..8b2c839f837 --- /dev/null +++ b/library/std/src/sys/thread_local/mod.rs @@ -0,0 +1,124 @@ +#![unstable(feature = "thread_local_internals", reason = "should not be necessary", issue = "none")] + +// There are three thread-local implementations: "static", "fast", "OS". +// The "OS" thread local key type is accessed via platform-specific API calls and is slow, while the +// "fast" key type is accessed via code generated via LLVM, where TLS keys are set up by the linker. +// "static" is for single-threaded platforms where a global static is sufficient. + +cfg_if::cfg_if! { + if #[cfg(any(all(target_family = "wasm", not(target_feature = "atomics")), target_os = "uefi"))] { + #[doc(hidden)] + mod static_local; + #[doc(hidden)] + pub use static_local::{Key, thread_local_inner}; + } else if #[cfg(target_thread_local)] { + #[doc(hidden)] + mod fast_local; + #[doc(hidden)] + pub use fast_local::{Key, thread_local_inner}; + } else { + #[doc(hidden)] + mod os_local; + #[doc(hidden)] + pub use os_local::{Key, thread_local_inner}; + } +} + +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> { + // SAFETY: The caller must ensure no reference is ever handed out to + // the inner cell nor mutable reference to the Option<T> inside said + // cell. This make it safe to hand a reference, though the lifetime + // of 'static is itself unsafe, making the get method unsafe. + unsafe { (*self.inner.get()).as_ref() } + } + + /// The caller must ensure that no reference is active: this method + /// needs unique access. + 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(); + + // SAFETY: + // + // 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. + // + // The precondition also ensures that we are the only one accessing + // `self` at the moment so replacing is fine. + unsafe { + let _ = mem::replace(&mut *ptr, Some(value)); + } + + // SAFETY: With the call to `mem::replace` it is guaranteed there is + // a `Some` behind `ptr`, not a `None` so `unreachable_unchecked` + // will never be reached. + unsafe { + // 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(), + } + } + } + + /// The other methods hand out references while taking &self. + /// As such, callers of this method must ensure no `&` and `&mut` are + /// available and used at the same time. + #[allow(unused)] + pub unsafe fn take(&mut self) -> Option<T> { + // SAFETY: See doc comment for this method. + unsafe { (*self.inner.get()).take() } + } + } +} + +/// Run a callback in a scenario which must not unwind (such as a `extern "C" +/// fn` declared in a user crate). If the callback unwinds anyway, then +/// `rtabort` with a message about thread local panicking on drop. +#[inline] +pub fn abort_on_dtor_unwind(f: impl FnOnce()) { + // Using a guard like this is lower cost. + let guard = DtorUnwindGuard; + f(); + core::mem::forget(guard); + + struct DtorUnwindGuard; + impl Drop for DtorUnwindGuard { + #[inline] + fn drop(&mut self) { + // This is not terribly descriptive, but it doesn't need to be as we'll + // already have printed a panic message at this point. + rtabort!("thread local panicked on drop"); + } + } +} diff --git a/library/std/src/sys/thread_local/os_local.rs b/library/std/src/sys/thread_local/os_local.rs new file mode 100644 index 00000000000..3edffd7e443 --- /dev/null +++ b/library/std/src/sys/thread_local/os_local.rs @@ -0,0 +1,185 @@ +use super::lazy::LazyKeyInner; +use crate::cell::Cell; +use crate::sys_common::thread_local_key::StaticKey as OsStaticKey; +use crate::{fmt, marker, panic, ptr}; + +#[doc(hidden)] +#[allow_internal_unstable(thread_local_internals)] +#[allow_internal_unsafe] +#[unstable(feature = "thread_local_internals", issue = "none")] +#[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) => {{ + #[inline] + #[deny(unsafe_op_in_unsafe_fn)] + unsafe fn __getit( + _init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + const INIT_EXPR: $t = $init; + + // On platforms without `#[thread_local]` we fall back to the + // same implementation as below for os thread locals. + #[inline] + const fn __init() -> $t { INIT_EXPR } + static __KEY: $crate::thread::local_impl::Key<$t> = + $crate::thread::local_impl::Key::new(); + unsafe { + __KEY.get(move || { + if let $crate::option::Option::Some(init) = _init { + if let $crate::option::Option::Some(value) = init.take() { + return value; + } else if $crate::cfg!(debug_assertions) { + $crate::unreachable!("missing initial value"); + } + } + __init() + }) + } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + }}, + + // used to generate the `LocalKey` value for `thread_local!` + (@key $t:ty, $init:expr) => { + { + #[inline] + fn __init() -> $t { $init } + + // `#[inline] does not work on windows-gnu due to linking errors around dllimports. + // See https://github.com/rust-lang/rust/issues/109797. + #[cfg_attr(not(windows), inline)] + unsafe fn __getit( + init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + static __KEY: $crate::thread::local_impl::Key<$t> = + $crate::thread::local_impl::Key::new(); + + unsafe { + __KEY.get(move || { + if let $crate::option::Option::Some(init) = init { + if let $crate::option::Option::Some(value) = init.take() { + return value; + } else if $crate::cfg!(debug_assertions) { + $crate::unreachable!("missing default value"); + } + } + __init() + }) + } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + } + }, + ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => { + $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> = + $crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*); + }, +} + +/// Use a regular global static to store this key; the state provided will then be +/// thread-local. +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.debug_struct("Key").finish_non_exhaustive() + } +} + +unsafe impl<T> Sync for Key<T> {} + +struct Value<T: 'static> { + inner: LazyKeyInner<T>, + key: &'static Key<T>, +} + +impl<T: 'static> Key<T> { + #[rustc_const_unstable(feature = "thread_local_internals", issue = "none")] + pub const fn new() -> Key<T> { + Key { os: OsStaticKey::new(Some(destroy_value::<T>)), marker: marker::PhantomData } + } + + /// It is a requirement for the caller to ensure that no mutable + /// reference is active when this method is called. + pub unsafe fn get(&'static self, init: impl FnOnce() -> T) -> Option<&'static T> { + // SAFETY: See the documentation for this method. + let ptr = unsafe { self.os.get() as *mut Value<T> }; + if ptr.addr() > 1 { + // SAFETY: the check ensured the pointer is safe (its destructor + // is not running) + it is coming from a trusted source (self). + if let Some(ref value) = unsafe { (*ptr).inner.get() } { + return Some(value); + } + } + // SAFETY: At this point we are sure we have no value and so + // initializing (or trying to) is safe. + unsafe { 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: impl FnOnce() -> T) -> Option<&'static T> { + // SAFETY: No mutable references are ever handed out meaning getting + // the value is ok. + let ptr = unsafe { self.os.get() as *mut Value<T> }; + if ptr.addr() == 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::into_raw(Box::new(Value { inner: LazyKeyInner::new(), key: self })); + // SAFETY: At this point we are sure there is no value inside + // ptr so setting it will not affect anyone else. + unsafe { + self.os.set(ptr as *mut u8); + } + ptr + } else { + // recursive initialization + ptr + }; + + // SAFETY: ptr has been ensured as non-NUL just above an so can be + // dereferenced safely. + unsafe { Some((*ptr).inner.initialize(init)) } + } +} + +unsafe extern "C" fn destroy_value<T: 'static>(ptr: *mut u8) { + // SAFETY: + // + // 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. + // + // Wrap the call in a catch to ensure unwinding is caught in the event + // a panic takes place in a destructor. + if let Err(_) = panic::catch_unwind(|| unsafe { + let ptr = Box::from_raw(ptr as *mut Value<T>); + let key = ptr.key; + key.os.set(ptr::without_provenance_mut(1)); + drop(ptr); + key.os.set(ptr::null_mut()); + }) { + rtabort!("thread local panicked on drop"); + } +} diff --git a/library/std/src/sys/thread_local/static_local.rs b/library/std/src/sys/thread_local/static_local.rs new file mode 100644 index 00000000000..4f2b6868962 --- /dev/null +++ b/library/std/src/sys/thread_local/static_local.rs @@ -0,0 +1,108 @@ +use super::lazy::LazyKeyInner; +use crate::fmt; + +#[doc(hidden)] +#[allow_internal_unstable(thread_local_internals)] +#[allow_internal_unsafe] +#[unstable(feature = "thread_local_internals", issue = "none")] +#[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) => {{ + #[inline] // see comments below + #[deny(unsafe_op_in_unsafe_fn)] + // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint + #[cfg_attr(bootstrap, allow(static_mut_ref))] + #[cfg_attr(not(bootstrap), allow(static_mut_refs))] + unsafe fn __getit( + _init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + const INIT_EXPR: $t = $init; + + // wasm without atomics maps directly to `static mut`, and dtors + // aren't implemented because thread dtors aren't really a thing + // on wasm right now + // + // FIXME(#84224) this should come after the `target_thread_local` + // block. + static mut VAL: $t = INIT_EXPR; + unsafe { $crate::option::Option::Some(&VAL) } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + }}, + + // used to generate the `LocalKey` value for `thread_local!` + (@key $t:ty, $init:expr) => { + { + #[inline] + fn __init() -> $t { $init } + #[inline] + unsafe fn __getit( + init: $crate::option::Option<&mut $crate::option::Option<$t>>, + ) -> $crate::option::Option<&'static $t> { + static __KEY: $crate::thread::local_impl::Key<$t> = + $crate::thread::local_impl::Key::new(); + + unsafe { + __KEY.get(move || { + if let $crate::option::Option::Some(init) = init { + if let $crate::option::Option::Some(value) = init.take() { + return value; + } else if $crate::cfg!(debug_assertions) { + $crate::unreachable!("missing default value"); + } + } + __init() + }) + } + } + + unsafe { + $crate::thread::LocalKey::new(__getit) + } + } + }, + ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => { + $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> = + $crate::thread::local_impl::thread_local_inner!(@key $t, $($init)*); + }, +} + +/// On some targets like wasm there's no threads, so no need to generate +/// thread locals and we can instead just use plain statics! + +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.debug_struct("Key").finish_non_exhaustive() + } +} + +impl<T> Key<T> { + pub const fn new() -> Key<T> { + Key { inner: LazyKeyInner::new() } + } + + pub unsafe fn get(&self, init: impl FnOnce() -> T) -> Option<&'static T> { + // SAFETY: The caller must ensure no reference is ever handed out to + // the inner cell nor mutable reference to the Option<T> inside said + // cell. This make it safe to hand a reference, though the lifetime + // of 'static is itself unsafe, making the get method unsafe. + let value = unsafe { + match self.inner.get() { + Some(ref value) => value, + None => self.inner.initialize(init), + } + }; + + Some(value) + } +} |