Macro std::thread_local
1.0.0 · source · macro_rules! thread_local { () => { ... }; ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const $init:block; $($rest:tt)*) => { ... }; ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = const $init:block) => { ... }; ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr; $($rest:tt)*) => { ... }; ($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty = $init:expr) => { ... }; }
Expand description
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);
static BAR: RefCell<f32> = RefCell::new(1.0);
}
FOO.with_borrow(|v| assert_eq!(*v, 1));
BAR.with_borrow(|v| assert_eq!(*v, 1.0));
RunNote that only shared references (&T
) to the inner data may be obtained, so a
type such as Cell
or RefCell
is typically used to allow mutating access.
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, 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) };
}
assert_eq!(FOO.get(), 1);
RunSee LocalKey
documentation for more
information.