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use crate::loom::thread::LocalKey;
use std::cell::Cell;
use std::marker;
/// Sets a reference as a thread-local.
macro_rules! scoped_thread_local {
($(#[$attrs:meta])* $vis:vis static $name:ident: $ty:ty) => (
$(#[$attrs])*
$vis static $name: $crate::macros::scoped_tls::ScopedKey<$ty>
= $crate::macros::scoped_tls::ScopedKey {
inner: {
thread_local!(static FOO: ::std::cell::Cell<*const ()> = {
std::cell::Cell::new(::std::ptr::null())
});
&FOO
},
_marker: ::std::marker::PhantomData,
};
)
}
/// Type representing a thread local storage key corresponding to a reference
/// to the type parameter `T`.
pub(crate) struct ScopedKey<T> {
pub(crate) inner: &'static LocalKey<Cell<*const ()>>,
pub(crate) _marker: marker::PhantomData<T>,
}
unsafe impl<T> Sync for ScopedKey<T> {}
impl<T> ScopedKey<T> {
/// Inserts a value into this scoped thread local storage slot for a
/// duration of a closure.
pub(crate) fn set<F, R>(&'static self, t: &T, f: F) -> R
where
F: FnOnce() -> R,
{
struct Reset {
key: &'static LocalKey<Cell<*const ()>>,
val: *const (),
}
impl Drop for Reset {
fn drop(&mut self) {
self.key.with(|c| c.set(self.val));
}
}
let prev = self.inner.with(|c| {
let prev = c.get();
c.set(t as *const _ as *const ());
prev
});
let _reset = Reset {
key: self.inner,
val: prev,
};
f()
}
/// Gets a value out of this scoped variable.
pub(crate) fn with<F, R>(&'static self, f: F) -> R
where
F: FnOnce(Option<&T>) -> R,
{
let val = self.inner.with(|c| c.get());
if val.is_null() {
f(None)
} else {
unsafe { f(Some(&*(val as *const T))) }
}
}
}
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