<commit_before>//! Thread local storage

#![unstable(feature = "thread_local_internals", issue = "0")]

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 = "0")]
#[macro_export]
#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)]
#[allow_internal_unsafe]
macro_rules! __thread_local_inner {
    (@key $(#[$attr:meta])* $vis:vis $name:ident, $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 $(#[$attr])* $vis $name, $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 = "0")]
    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 it is destroyed")
    }

    /// 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")]
    pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError>
    where
        F: FnOnce(&T) -> R,<commit_msg>updated the panic message wording<commit_after>//! Thread local storage

#![unstable(feature = "thread_local_internals", issue = "0")]

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 = "0")]
#[macro_export]
#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)]
#[allow_internal_unsafe]
macro_rules! __thread_local_inner {
    (@key $(#[$attr:meta])* $vis:vis $name:ident, $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 $(#[$attr])* $vis $name, $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 = "0")]
    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")]
    pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError>
    where
        F: FnOnce(&T) -> R,
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