-
-
Notifications
You must be signed in to change notification settings - Fork 2.5k
New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
task: Introduce a new pattern for task-local storage #2126
Merged
Merged
Changes from all commits
Commits
File filter
Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,240 @@ | ||
use pin_project_lite::pin_project; | ||
use std::cell::RefCell; | ||
use std::error::Error; | ||
use std::future::Future; | ||
use std::pin::Pin; | ||
use std::task::{Context, Poll}; | ||
use std::{fmt, thread}; | ||
|
||
/// Declare a new task local storage key of type [`tokio::task::LocalKey`]. | ||
/// | ||
/// # Syntax | ||
/// | ||
/// The macro wraps any number of static declarations and makes them task locals. | ||
/// Publicity and attributes for each static are allowed. | ||
/// | ||
/// # Examples | ||
/// | ||
/// ``` | ||
/// # use tokio::task_local; | ||
/// task_local! { | ||
/// pub static FOO: u32; | ||
/// | ||
/// #[allow(unused)] | ||
/// static BAR: f32; | ||
/// } | ||
/// # fn main() {} | ||
/// ``` | ||
/// | ||
/// See [LocalKey documentation][`tokio::task::LocalKey`] for more | ||
/// information. | ||
/// | ||
/// [`tokio::task::LocalKey`]: ../tokio/task/struct.LocalKey.html | ||
#[macro_export] | ||
macro_rules! task_local { | ||
// empty (base case for the recursion) | ||
() => {}; | ||
|
||
($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty; $($rest:tt)*) => { | ||
$crate::__task_local_inner!($(#[$attr])* $vis $name, $t); | ||
$crate::task_local!($($rest)*); | ||
}; | ||
|
||
($(#[$attr:meta])* $vis:vis static $name:ident: $t:ty) => { | ||
$crate::__task_local_inner!($(#[$attr])* $vis $name, $t); | ||
} | ||
} | ||
|
||
#[doc(hidden)] | ||
#[macro_export] | ||
macro_rules! __task_local_inner { | ||
($(#[$attr:meta])* $vis:vis $name:ident, $t:ty) => { | ||
static $name: $crate::task::LocalKey<$t> = { | ||
std::thread_local! { | ||
static __KEY: std::cell::RefCell<Option<$t>> = std::cell::RefCell::new(None); | ||
} | ||
|
||
$crate::task::LocalKey { inner: __KEY } | ||
}; | ||
}; | ||
} | ||
|
||
/// A key for task-local data. | ||
/// | ||
/// This type is generated by `task_local!` macro and unlike `thread_local!` it has | ||
/// no concept of lazily initialization. Instead, it is designed to provide task local | ||
/// storage the future that is passed to `set`. | ||
/// | ||
/// # Initialization and Destruction | ||
/// | ||
/// Initialization is done via `set` which is an `async fn` that wraps another | ||
/// [`std::future::Future`] and will set the value on each `Future::poll` call. | ||
/// Once the `set` future is dropped the corresponding task local value is also | ||
/// dropped. | ||
/// | ||
/// # Examples | ||
/// | ||
/// ``` | ||
/// # async fn dox() { | ||
/// tokio::task_local! { | ||
/// static FOO: u32; | ||
/// } | ||
/// | ||
/// FOO.scope(1, async move { | ||
/// assert_eq!(FOO.get(), 1); | ||
/// }).await; | ||
/// | ||
/// FOO.scope(2, async move { | ||
/// assert_eq!(FOO.get(), 2); | ||
/// | ||
/// FOO.scope(3, async move { | ||
/// assert_eq!(FOO.get(), 3); | ||
/// }).await; | ||
/// }).await; | ||
/// # } | ||
/// ``` | ||
pub struct LocalKey<T: 'static> { | ||
#[doc(hidden)] | ||
pub inner: thread::LocalKey<RefCell<Option<T>>>, | ||
} | ||
|
||
impl<T: 'static> LocalKey<T> { | ||
/// Sets a value `T` as the task local value for the future `F`. | ||
/// | ||
/// This will run the provided future to completion and set the | ||
/// provided value as the task local under this key. Once the returned | ||
/// future is dropped so will the value passed be dropped. | ||
/// | ||
/// # async fn dox() { | ||
/// tokio::task_local! { | ||
/// static FOO: u32; | ||
/// } | ||
/// | ||
/// FOO.scope(1, async move { | ||
/// println!("task local value: {}", FOO.get()); | ||
/// }).await; | ||
/// # } | ||
pub async fn scope<F>(&'static self, value: T, f: F) -> F::Output | ||
where | ||
F: Future, | ||
{ | ||
TaskLocalFuture { | ||
local: &self, | ||
slot: Some(value), | ||
future: f, | ||
} | ||
.await | ||
} | ||
|
||
/// Access this task-local key, running the provided closure with a reference | ||
/// passed to the value. | ||
/// | ||
/// # Panics | ||
/// | ||
/// This function will panic if not called within a future that has not been | ||
/// set via `LocalKey::set`. | ||
pub fn with<F, R>(&'static self, f: F) -> R | ||
where | ||
F: FnOnce(&T) -> R, | ||
{ | ||
self.try_with(f).expect( | ||
"cannot access a Task Local Storage value \ | ||
without setting it via `LocalKey::set`", | ||
) | ||
} | ||
|
||
/// Access this task-local key, running the provided closure with a reference | ||
/// passed to the value. Unlike `with` this function will return a `Result<R, AccessError>` | ||
/// instead of panicking. | ||
pub fn try_with<F, R>(&'static self, f: F) -> Result<R, AccessError> | ||
where | ||
F: FnOnce(&T) -> R, | ||
{ | ||
self.inner.with(|v| { | ||
if let Some(val) = v.borrow().as_ref() { | ||
Ok(f(val)) | ||
} else { | ||
Err(AccessError { _private: () }) | ||
} | ||
}) | ||
} | ||
} | ||
|
||
impl<T: Copy + 'static> LocalKey<T> { | ||
/// Get a copy of the task-local value if it implements | ||
/// the `Copy` trait. | ||
pub fn get(&'static self) -> T { | ||
self.with(|v| *v) | ||
} | ||
} | ||
|
||
impl<T: 'static> fmt::Debug for LocalKey<T> { | ||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
f.pad("LocalKey { .. }") | ||
} | ||
} | ||
|
||
pin_project! { | ||
struct TaskLocalFuture<T: StaticLifetime, F> { | ||
local: &'static LocalKey<T>, | ||
slot: Option<T>, | ||
#[pin] | ||
future: F, | ||
} | ||
} | ||
|
||
impl<T: 'static, F: Future> Future for TaskLocalFuture<T, F> { | ||
type Output = F::Output; | ||
|
||
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { | ||
struct Guard<'a, T: 'static> { | ||
local: &'static LocalKey<T>, | ||
slot: &'a mut Option<T>, | ||
prev: Option<T>, | ||
} | ||
|
||
impl<T> Drop for Guard<'_, T> { | ||
fn drop(&mut self) { | ||
let value = self.local.inner.with(|c| c.replace(self.prev.take())); | ||
*self.slot = value; | ||
} | ||
} | ||
|
||
let mut project = self.project(); | ||
let val = project.slot.take(); | ||
|
||
let prev = project.local.inner.with(|c| c.replace(val)); | ||
|
||
let _guard = Guard { | ||
prev, | ||
slot: &mut project.slot, | ||
local: *project.local, | ||
}; | ||
|
||
project.future.poll(cx) | ||
} | ||
} | ||
|
||
// Required to make `pin_project` happy. | ||
trait StaticLifetime: 'static {} | ||
impl<T: 'static> StaticLifetime for T {} | ||
|
||
/// An error returned by [`LocalKey::try_with`](struct.LocalKey.html#method.try_with). | ||
#[derive(Clone, Copy, Eq, PartialEq)] | ||
pub struct AccessError { | ||
_private: (), | ||
} | ||
|
||
impl fmt::Debug for AccessError { | ||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
f.debug_struct("AccessError").finish() | ||
} | ||
} | ||
|
||
impl fmt::Display for AccessError { | ||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
fmt::Display::fmt("task-local value not set", f) | ||
} | ||
} | ||
|
||
impl Error for AccessError {} |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,31 @@ | ||
tokio::task_local! { | ||
static REQ_ID: u32; | ||
pub static FOO: bool; | ||
} | ||
|
||
#[tokio::test(threaded_scheduler)] | ||
async fn local() { | ||
let j1 = tokio::spawn(REQ_ID.scope(1, async move { | ||
assert_eq!(REQ_ID.get(), 1); | ||
assert_eq!(REQ_ID.get(), 1); | ||
})); | ||
|
||
let j2 = tokio::spawn(REQ_ID.scope(2, async move { | ||
REQ_ID.with(|v| { | ||
assert_eq!(REQ_ID.get(), 2); | ||
assert_eq!(*v, 2); | ||
}); | ||
|
||
tokio::time::delay_for(std::time::Duration::from_millis(10)).await; | ||
|
||
assert_eq!(REQ_ID.get(), 2); | ||
})); | ||
|
||
let j3 = tokio::spawn(FOO.scope(true, async move { | ||
assert!(FOO.get()); | ||
})); | ||
|
||
j1.await.unwrap(); | ||
j2.await.unwrap(); | ||
j3.await.unwrap(); | ||
} |
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
I'm not super familiar with how thread-locals are implemented. Do they when defined use memory on every thread - even if that one doesn't make use of them? Or is it lazily allocated? If it requires memory everywhere then adding lots of task-locals will obviously make it worse. But on the other hand I don't expect people to use too many task-locals with this kind declaration mechanism.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
IIRC, thread-local pages are copy-on-write.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
https://akkadia.org/drepper/tls.pdf