diff options
Diffstat (limited to 'library/std/src/thread/local.rs')
| -rw-r--r-- | library/std/src/thread/local.rs | 34 |
1 files changed, 26 insertions, 8 deletions
diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs index 7fdf03acc..1b86d898c 100644 --- a/library/std/src/thread/local.rs +++ b/library/std/src/thread/local.rs @@ -18,8 +18,8 @@ use crate::fmt; /// 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. +/// The [`with`] method yields a reference to the contained value which cannot +/// outlive the current thread or escape the given closure. /// /// [`thread_local!`]: crate::thread_local /// @@ -134,10 +134,28 @@ impl<T: 'static> fmt::Debug for LocalKey<T> { /// thread_local! { /// pub static FOO: RefCell<u32> = RefCell::new(1); /// -/// #[allow(unused)] /// static BAR: RefCell<f32> = RefCell::new(1.0); /// } -/// # fn main() {} +/// +/// FOO.with(|foo| assert_eq!(*foo.borrow(), 1)); +/// BAR.with(|bar| assert_eq!(*bar.borrow(), 1.0)); +/// ``` +/// +/// This macro supports a special `const {}` syntax that can be used +/// when the initialization expression can be evaluated as a constant. +/// This can enable a more efficient thread local implementation that +/// can avoid lazy initialization. For types that do not +/// [need to be dropped][crate::mem::needs_drop], this can enable an +/// even more efficient implementation that does not need to +/// track any additional state. +/// +/// ``` +/// use std::cell::Cell; +/// thread_local! { +/// pub static FOO: Cell<u32> = const { Cell::new(1) }; +/// } +/// +/// FOO.with(|foo| assert_eq!(foo.get(), 1)); /// ``` /// /// See [`LocalKey` documentation][`std::thread::LocalKey`] for more @@ -153,23 +171,23 @@ macro_rules! thread_local { () => {}; ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }; $($rest:tt)*) => ( - $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, const $init); + $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, const $init); $crate::thread_local!($($rest)*); ); ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const { $init:expr }) => ( - $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, const $init); + $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, const $init); ); // process multiple declarations ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => ( - $crate::__thread_local_inner!($(#[$attr])* $vis $name, $t, $init); + $crate::thread::local_impl::thread_local_inner!($(#[$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); + $crate::thread::local_impl::thread_local_inner!($(#[$attr])* $vis $name, $t, $init); ); } |