blob: 770912b219a098115544f84bf49871e188f0a13b [file] [log] [blame]
use std::prelude::v1::*;
use std::any::TypeId;
use std::cell::RefCell;
use std::hash::{BuildHasherDefault, Hasher};
use std::collections::HashMap;
use task_impl::with;
/// A macro to create a `static` of type `LocalKey`
///
/// This macro is intentionally similar to the `thread_local!`, and creates a
/// `static` which has a `with` method to access the data on a task.
///
/// The data associated with each task local is per-task, so different tasks
/// will contain different values.
#[macro_export]
macro_rules! task_local {
(static $NAME:ident: $t:ty = $e:expr) => (
static $NAME: $crate::task::LocalKey<$t> = {
fn __init() -> $t { $e }
fn __key() -> ::std::any::TypeId {
struct __A;
::std::any::TypeId::of::<__A>()
}
$crate::task::LocalKey {
__init: __init,
__key: __key,
}
};
)
}
pub type LocalMap = RefCell<HashMap<TypeId,
Box<Opaque>,
BuildHasherDefault<IdHasher>>>;
pub fn local_map() -> LocalMap {
RefCell::new(HashMap::default())
}
pub trait Opaque: Send {}
impl<T: Send> Opaque for T {}
/// A key for task-local data stored in a future's task.
///
/// This type is generated by the `task_local!` macro and performs very
/// similarly to the `thread_local!` macro and `std::thread::LocalKey` types.
/// Data associated with a `LocalKey<T>` is stored inside of a future's task,
/// and the data is destroyed when the future is completed and the task is
/// destroyed.
///
/// Task-local data can migrate between threads and hence requires a `Send`
/// bound. Additionally, task-local data also requires the `'static` bound to
/// ensure it lives long enough. When a key is accessed for the first time the
/// task's data is initialized with the provided initialization expression to
/// the macro.
#[derive(Debug)]
pub struct LocalKey<T> {
// "private" fields which have to be public to get around macro hygiene, not
// included in the stability story for this type. Can change at any time.
#[doc(hidden)]
pub __key: fn() -> TypeId,
#[doc(hidden)]
pub __init: fn() -> T,
}
pub struct IdHasher {
id: u64,
}
impl Default for IdHasher {
fn default() -> IdHasher {
IdHasher { id: 0 }
}
}
impl Hasher for IdHasher {
fn write(&mut self, _bytes: &[u8]) {
// TODO: need to do something sensible
panic!("can only hash u64");
}
fn write_u64(&mut self, u: u64) {
self.id = u;
}
fn finish(&self) -> u64 {
self.id
}
}
impl<T: Send + 'static> LocalKey<T> {
/// Access this task-local key, running the provided closure with a
/// reference to the value.
///
/// This function will access this task-local key to retrieve the data
/// associated with the current task and this key. If this is the first time
/// this key has been accessed on this task, then the key will be
/// initialized with the initialization expression provided at the time the
/// `task_local!` macro was called.
///
/// The provided closure will be provided a shared reference to the
/// underlying data associated with this task-local-key. The data itself is
/// stored inside of the current task.
///
/// # Panics
///
/// This function can possibly panic for a number of reasons:
///
/// * If there is not a current task.
/// * If the initialization expression is run and it panics
/// * If the closure provided panics
pub fn with<F, R>(&'static self, f: F) -> R
where F: FnOnce(&T) -> R
{
let key = (self.__key)();
with(|task| {
let raw_pointer = {
let mut data = task.map.borrow_mut();
let entry = data.entry(key).or_insert_with(|| {
Box::new((self.__init)())
});
&**entry as *const Opaque as *const T
};
unsafe {
f(&*raw_pointer)
}
})
}
}