/
context.rs
66 lines (56 loc) · 1.77 KB
/
context.rs
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//! Thread local runtime context
use crate::runtime::{Handle, TryCurrentError};
use crate::util::{replace_thread_rng, RngSeed};
use std::cell::RefCell;
tokio_thread_local! {
static CONTEXT: RefCell<Option<Handle>> = const { RefCell::new(None) }
}
pub(crate) fn try_current() -> Result<Handle, crate::runtime::TryCurrentError> {
match CONTEXT.try_with(|ctx| ctx.borrow().clone()) {
Ok(Some(handle)) => Ok(handle),
Ok(None) => Err(TryCurrentError::new_no_context()),
Err(_access_error) => Err(TryCurrentError::new_thread_local_destroyed()),
}
}
#[track_caller]
pub(crate) fn current() -> Handle {
match try_current() {
Ok(handle) => handle,
Err(e) => panic!("{}", e),
}
}
/// Sets this [`Handle`] as the current active [`Handle`].
///
/// [`Handle`]: Handle
pub(crate) fn enter(new: Handle) -> EnterGuard {
match try_enter(new) {
Some(guard) => guard,
None => panic!("{}", crate::util::error::THREAD_LOCAL_DESTROYED_ERROR),
}
}
/// Sets this [`Handle`] as the current active [`Handle`].
///
/// [`Handle`]: Handle
pub(crate) fn try_enter(new: Handle) -> Option<EnterGuard> {
let rng_seed = new.inner.seed_generator().next_seed();
let old_handle = CONTEXT.try_with(|ctx| ctx.borrow_mut().replace(new)).ok()?;
let old_seed = replace_thread_rng(rng_seed);
Some(EnterGuard {
old_handle,
old_seed,
})
}
#[derive(Debug)]
pub(crate) struct EnterGuard {
old_handle: Option<Handle>,
old_seed: RngSeed,
}
impl Drop for EnterGuard {
fn drop(&mut self) {
CONTEXT.with(|ctx| {
*ctx.borrow_mut() = self.old_handle.take();
});
// We discard the RngSeed associated with this guard
let _ = replace_thread_rng(self.old_seed.clone());
}
}