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utils: add DetachableTask & ContextGuard (#2138)
This commit is contained in:
Luna Yao
@@ -0,0 +1,638 @@
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//! # Guard Module Utilities
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//!
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//! This module provides mechanisms for scope-based resource management and deferred execution.
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//!
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//! ### ⚠️ Critical Usage Note: Diverging Expressions
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//!
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//! Do not use "naked" diverging expressions—such as `panic!`, `todo!`, or `loop {}`—as
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//! the sole content of sync guard closure. This prevents the compiler from
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//! distinguishing between synchronous (`ASYNC = false`) and asynchronous
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//! (`ASYNC = true`) implementations, leading to a type inference error (E0277).
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//!
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//! ### Technical Context
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//!
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//! The `!` (Never Type) is a bottom type that can be coerced into any other type.
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//! Because it satisfies both the `()` requirement for sync guards and the `Future`
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//! requirement for async guards, the compiler encounters an inference deadlock.
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//!
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//! ### Workaround
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//!
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//! For macros like `guard!` or `guarded!`, force the closure to resolve to `()`
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//! by explicitly setting the guard to `sync`:
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//!
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//! ```rust
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//! let _g = guard!([val] sync {
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//! panic!("critical failure");
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//! });
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//! ```
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use crate::utils::task::{DetachableTask, TaskSpawner};
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use std::fmt::Debug;
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use std::mem::ManuallyDrop;
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use std::ops::{Deref, DerefMut};
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pub trait CallableGuard<const ASYNC: bool, Context> {
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type Output;
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fn call(self, context: Context) -> Self::Output;
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}
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impl<Context, Guard> CallableGuard<false, Context> for Guard
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where
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Guard: FnOnce(Context),
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{
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type Output = ();
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fn call(self, context: Context) -> Self::Output {
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self(context)
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}
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}
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impl<Context, Guard, Task, _R> CallableGuard<true, Context> for Guard
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where
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Guard: FnOnce(Context) -> Task + Send + 'static,
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Task: Future<Output = _R> + Send + 'static,
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_R: Send + 'static,
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{
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type Output = DetachableTask<TaskSpawner<Task>, Task>;
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fn call(self, context: Context) -> Self::Output {
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DetachableTask::new(self(context))
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}
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}
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pub struct ContextGuard<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>> {
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context: ManuallyDrop<Context>,
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guard: ManuallyDrop<Guard>,
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}
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impl<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>> Deref
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for ContextGuard<ASYNC, Context, Guard>
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{
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type Target = Context;
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fn deref(&self) -> &Self::Target {
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&self.context
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}
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}
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impl<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>> DerefMut
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for ContextGuard<ASYNC, Context, Guard>
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{
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fn deref_mut(&mut self) -> &mut Self::Target {
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&mut self.context
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}
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}
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impl<const ASYNC: bool, Context: Debug, Guard: CallableGuard<ASYNC, Context>> Debug
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for ContextGuard<ASYNC, Context, Guard>
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{
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fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
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let name = if ASYNC {
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"ContextGuard::Async"
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} else {
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"ContextGuard::Sync"
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};
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f.debug_struct(name)
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.field("context", &self.context)
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.finish_non_exhaustive()
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}
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}
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impl<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>>
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ContextGuard<ASYNC, Context, Guard>
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{
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/// Creates a new `ContextGuard`.
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///
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/// **Note on generics:** The seemingly unused `_R` generic parameter and the
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/// `Guard: FnOnce(Context) -> _R` trait bound are intentionally included.
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/// They act as a hint to help the compiler infer closure types.
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pub fn new<_R>(context: Context, guard: Guard) -> Self
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where
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Guard: FnOnce(Context) -> _R,
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{
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ContextGuard {
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context: ManuallyDrop::new(context),
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guard: ManuallyDrop::new(guard),
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}
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}
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}
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impl<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>>
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ContextGuard<ASYNC, Context, Guard>
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{
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unsafe fn call(&mut self) -> Guard::Output {
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unsafe {
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let context = ManuallyDrop::take(&mut self.context);
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let guard = ManuallyDrop::take(&mut self.guard);
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guard.call(context)
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}
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}
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pub fn trigger(self) -> Guard::Output {
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let mut this = ManuallyDrop::new(self);
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unsafe { this.call() }
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}
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pub fn defuse(self) -> Context {
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let mut this = ManuallyDrop::new(self);
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unsafe {
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ManuallyDrop::drop(&mut this.guard);
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ManuallyDrop::take(&mut this.context)
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}
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}
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}
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impl<const ASYNC: bool, Context, Guard: CallableGuard<ASYNC, Context>> Drop
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for ContextGuard<ASYNC, Context, Guard>
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{
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fn drop(&mut self) {
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let _: Guard::Output = unsafe { self.call() };
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}
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}
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// region macro
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#[doc(hidden)]
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#[macro_export]
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macro_rules! __guarded {
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(@parse@action $guard:ident => $($tt:tt)*) => {
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$crate::__guarded! { @parse@async action: [ @stmt $guard ] ; $($tt)* }
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};
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(@parse@action $($tt:tt)*) => {
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$crate::__guarded! { @parse@async action: [ @stmt __guard ] ; $($tt)* }
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};
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(@parse@async action: [ $($action:tt)* ] ; sync $($tt:tt)*) => {
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$crate::__guarded! { @parse@move action: [ $($action)* ] ; async: [ false ] ; $($tt)* }
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};
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(@parse@async action: [ $($action:tt)* ] ; $($tt:tt)*) => {
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$crate::__guarded! { @parse@move action: [ $($action)* ] ; async: [ _ ] ; $($tt)* }
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};
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(@parse@move action: [ $($action:tt)* ] ; async: [ $async:tt ] ; move $($tt:tt)*) => {
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$crate::__guarded! { @parse action: [ $($action)* ] ; async: [ $async ] ; move: [ move ] ; $($tt)* }
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};
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(@parse@move action: [ $($action:tt)* ] ; async: [ $async:tt ] ; $($tt:tt)*) => {
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$crate::__guarded! { @parse action: [ $($action)* ] ; async: [ $async ] ; move: [] ; $($tt)* }
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};
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(
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@parse action: [ $($action:tt)* ] ; async: [ $async:tt ] ; move: [ $($move:tt)? ] ;
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[ $($args:tt)* ] $body:block
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) => {
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$crate::__guarded! {
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action: [ $($action)* ]
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async: [ $async ]
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move: [ $($move)? ]
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mut: []
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rest: [ $($args)* , ]
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args: []
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vars: []
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body: [ $body ]
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}
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};
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(
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@parse action: [ $($action:tt)* ] ; async: [ $async:tt ] ; move: [ $($move:tt)? ] ;
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$body:block
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) => {
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$crate::__guarded! {
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@parse action: [ $($action)* ] ; async: [ $async ] ; move: [ $($move)? ] ;
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[] $body
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}
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};
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(
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@parse action: [ $($action:tt)* ] ; async: [ $async:tt ] ; move: [ $($move:tt)? ] ;
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[ $($args:tt)* ] $($body:tt)*
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) => {
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$crate::__guarded! {
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@parse action: [ $($action)* ] ; async: [ $async ] ; move: [ $($move)? ] ;
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[ $($args)* ] { $($body)* }
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}
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};
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(
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@parse action: [ $($action:tt)* ] ; async: [ $async:tt ] ; move: [ $($move:tt)? ] ;
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$($body:tt)*
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) => {
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$crate::__guarded! {
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@parse action: [ $($action)* ] ; async: [ $async ] ; move: [ $($move)? ] ;
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[] { $($body)* }
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}
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};
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(
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action: [ $($action:tt)* ]
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async: [ $async:tt ]
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move: [ $($move:tt)? ]
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mut: [ $($mut:tt)? ]
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rest: [ mut $arg:ident , $($rest:tt)* ]
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args: [ $($args:ident)* ]
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vars: [ $($vars:tt)* ]
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body: [ $body:expr ]
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) => {
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$crate::__guarded! {
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action: [ $($action)* ]
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async: [ $async ]
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move: [ $($move)? ]
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mut: [ mut ]
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rest: [ $($rest)* ]
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args: [ $($args)* $arg ]
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vars: [ $($vars)* [mut $arg] ]
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body: [ $body ]
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}
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};
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(
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action: [ $($action:tt)* ]
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async: [ $async:tt ]
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move: [ $($move:tt)? ]
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mut: [ $($mut:tt)? ]
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rest: [ $arg:ident , $($rest:tt)* ]
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args: [ $($args:ident)* ]
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vars: [ $($vars:tt)* ]
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body: [ $body:expr ]
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) => {
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$crate::__guarded! {
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action: [ $($action)* ]
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async: [ $async ]
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move: [ $($move)? ]
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mut: [ $($mut)? ]
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rest: [ $($rest)* ]
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args: [ $($args)* $arg ]
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vars: [ $($vars)* [$arg] ]
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body: [ $body ]
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}
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};
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(
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action: [ @stmt $guard:ident ]
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async: [ $async:tt ]
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move: [ $($move:tt)? ]
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mut: [ $($mut:tt)? ]
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rest: [ $(,)* ]
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args: [ $($args:ident)* ]
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vars: [ $([$($vars:tt)*])* ]
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body: [ $body:expr ]
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) => {
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let $($mut)? $guard = $crate::utils::guard::ContextGuard::<$async, _, _>::new(
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( $($args),* ),
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$($move)? |#[allow(unused_parens, unused_mut)] ( $($($vars)*),* )| $body
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);
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#[allow(unused_parens, unused_variables, clippy::toplevel_ref_arg)]
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let ( $(ref $($vars)*),* ) = *$guard;
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};
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(
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action: [ @expr ]
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async: [ $async:tt ]
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move: [ $($move:tt)? ]
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mut: [ $($mut:tt)? ]
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rest: [ $(,)* ]
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args: [ $($args:ident)* ]
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vars: [ $([$($vars:tt)*])* ]
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body: [ $body:expr ]
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) => {
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$crate::utils::guard::ContextGuard::<$async, _, _>::new(
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( $($args),* ),
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$($move)? |#[allow(unused_parens)] ( $($($vars)*),* )| $body
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)
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};
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}
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/// Creates a [`ContextGuard`] object, binding it to a variable with the specified name (e.g., `_guard`).
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/// Context variables specified in the macro invocation are available within and after the guard body.
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///
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/// **Note:** For usage with `panic!` or `loop`, see the [module-level documentation](self)
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/// regarding type inference deadlocks.
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#[macro_export]
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macro_rules! guarded {
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( $($tt:tt)* ) => {
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$crate::__guarded! { @parse@action $($tt)* }
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};
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}
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/// Creates a [`ContextGuard`] object, without binding it to a variable.
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/// Context variables specified in the macro invocation are available within the guard body.
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///
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/// **Note:** For usage with `panic!` or `loop`, see the [module-level documentation](self)
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/// regarding type inference deadlocks.
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#[macro_export]
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macro_rules! guard {
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( $($tt:tt)* ) => {
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$crate::__guarded! { @parse@async action: [ @expr ] ; $($tt)* }
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};
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}
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// endregion
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/// Alias for [`guarded!`].
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///
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/// **Note:** For usage with `panic!` or `loop`, see the [module-level documentation](self)
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/// regarding type inference deadlocks.
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#[macro_export]
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macro_rules! defer {
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( $($tt:tt)* ) => {
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$crate::guarded! { $($tt)* }
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};
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}
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#[cfg(test)]
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mod tests {
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use std::panic::catch_unwind;
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use std::sync::Arc;
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use std::sync::atomic::{AtomicUsize, Ordering};
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use std::time::Duration;
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use tokio::sync::oneshot;
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#[test]
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fn trigger_sync_executes_once() {
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let called = Arc::new(AtomicUsize::new(0));
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let observed = Arc::new(AtomicUsize::new(0));
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let value = 7usize;
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let guard = {
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let called = called.clone();
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let observed = observed.clone();
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crate::guard!(move [value] {
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called.fetch_add(1, Ordering::SeqCst);
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observed.store(value, Ordering::SeqCst);
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})
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};
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guard.trigger();
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assert_eq!(called.load(Ordering::SeqCst), 1);
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assert_eq!(observed.load(Ordering::SeqCst), 7);
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}
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#[test]
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fn defuse_sync_returns_context_without_running_guard() {
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let called = Arc::new(AtomicUsize::new(0));
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let value = String::from("hello");
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let guard = {
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let called = called.clone();
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crate::guard!(move [mut value] {
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value.push_str(" world");
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called.fetch_add(1, Ordering::SeqCst);
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})
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};
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let context = guard.defuse();
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assert_eq!(context, "hello");
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assert_eq!(called.load(Ordering::SeqCst), 0);
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}
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#[test]
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fn drop_sync_triggers_guard() {
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let called = Arc::new(AtomicUsize::new(0));
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{
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let called = called.clone();
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crate::guarded!([called] {
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called.fetch_add(1, Ordering::SeqCst);
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});
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}
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assert_eq!(called.load(Ordering::SeqCst), 1);
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}
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#[test]
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fn drop_propagates_guard_panic() {
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let dropped = catch_unwind(|| {
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guarded! {
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sync {
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panic!("boom");
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}
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}
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});
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assert!(dropped.is_err());
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}
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#[tokio::test]
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async fn trigger_async_returns_runnable_task() {
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let called = Arc::new(AtomicUsize::new(0));
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let value = 5usize;
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let guard = {
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let called = called.clone();
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crate::guard!(move [value] async move {
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called.fetch_add(value, Ordering::SeqCst);
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})
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};
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let task = guard.trigger();
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task.await;
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|
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assert_eq!(called.load(Ordering::SeqCst), 5);
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}
|
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|
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#[tokio::test]
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async fn drop_async_detaches_task() {
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let (tx, rx) = oneshot::channel();
|
||||
|
||||
{
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let mut tx = Some(tx);
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let value = 9usize;
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let _guard = crate::guard!(move [value] {
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let tx = tx.take();
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async move {
|
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if let Some(tx) = tx {
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let _ = tx.send(value);
|
||||
}
|
||||
}
|
||||
});
|
||||
}
|
||||
|
||||
let value = tokio::time::timeout(Duration::from_secs(1), rx)
|
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.await
|
||||
.expect("detached task should run")
|
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.expect("detached task should send value");
|
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assert_eq!(value, 9);
|
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}
|
||||
|
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#[tokio::test]
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async fn defuse_async_does_not_execute() {
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let called = Arc::new(AtomicUsize::new(0));
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||||
|
||||
let value = 11usize;
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||||
let guard = {
|
||||
let called = called.clone();
|
||||
crate::guard!(move [value] async move {
|
||||
called.fetch_add(value, Ordering::SeqCst);
|
||||
})
|
||||
};
|
||||
|
||||
let context = guard.defuse();
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||||
assert_eq!(context, 11);
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||||
|
||||
tokio::time::sleep(Duration::from_millis(20)).await;
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||||
assert_eq!(called.load(Ordering::SeqCst), 0);
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||||
}
|
||||
|
||||
#[test]
|
||||
fn guarded_named_mut_binding_updates_context_before_drop() {
|
||||
let committed = Arc::new(AtomicUsize::new(0));
|
||||
|
||||
{
|
||||
let value = 1usize;
|
||||
let step = 2usize;
|
||||
let committed = committed.clone();
|
||||
|
||||
crate::guarded!(scope_guard => [mut value, step] {
|
||||
committed.store(value + step, Ordering::SeqCst);
|
||||
});
|
||||
|
||||
*value += 10;
|
||||
assert_eq!(*value, 11);
|
||||
assert_eq!(*step, 2);
|
||||
|
||||
drop(scope_guard);
|
||||
}
|
||||
|
||||
assert_eq!(committed.load(Ordering::SeqCst), 13);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn guard_expression_parses_without_braces() {
|
||||
let observed = Arc::new(AtomicUsize::new(0));
|
||||
|
||||
let value = 3usize;
|
||||
let observed_clone = observed.clone();
|
||||
let guard = crate::guard!([value] observed_clone.store(value, Ordering::SeqCst));
|
||||
guard.trigger();
|
||||
|
||||
assert_eq!(observed.load(Ordering::SeqCst), 3);
|
||||
}
|
||||
|
||||
#[test]
|
||||
fn defer_alias_behaves_like_guarded_statement() {
|
||||
let called = Arc::new(AtomicUsize::new(0));
|
||||
|
||||
{
|
||||
let n = 42usize;
|
||||
let called = called.clone();
|
||||
crate::defer!([n] {
|
||||
called.store(n, Ordering::SeqCst);
|
||||
});
|
||||
}
|
||||
|
||||
assert_eq!(called.load(Ordering::SeqCst), 42);
|
||||
}
|
||||
|
||||
#[tokio::test]
|
||||
async fn guard_and_guarded_macro_usage_matrix() {
|
||||
// 1) guard!: block body + trailing comma args + trigger()
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
let v = 1usize;
|
||||
let sink_clone = sink.clone();
|
||||
let g1 = crate::guard!([v,] {
|
||||
sink_clone.store(v, Ordering::SeqCst);
|
||||
});
|
||||
g1.trigger();
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 1);
|
||||
|
||||
// 2) guard!: expression body (no braces)
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
let sink_clone = sink.clone();
|
||||
let v = 2usize;
|
||||
let g2 = crate::guard!([v] sink_clone.store(v, Ordering::SeqCst));
|
||||
g2.trigger();
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 2);
|
||||
|
||||
// 3) guard!: explicit sync + no args form
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
let sink_clone = sink.clone();
|
||||
let g3 = crate::guard!(sync {
|
||||
sink_clone.store(3, Ordering::SeqCst);
|
||||
});
|
||||
g3.trigger();
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 3);
|
||||
|
||||
// 4) guard!: move capture + defuse() prevents execution
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
let owned = String::from("owned");
|
||||
let sink_clone = sink.clone();
|
||||
let g4 = crate::guard!(move [owned] {
|
||||
if owned == "owned" {
|
||||
sink_clone.store(4, Ordering::SeqCst);
|
||||
}
|
||||
});
|
||||
let context = g4.defuse();
|
||||
assert_eq!(context, "owned");
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 0);
|
||||
|
||||
// 5) guard!: async block inference + trigger() returns task
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
let sink_clone = sink.clone();
|
||||
let n = 5usize;
|
||||
let g5 = crate::guard!([n] async move {
|
||||
sink_clone.fetch_add(n, Ordering::SeqCst);
|
||||
});
|
||||
g5.trigger().await;
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 5);
|
||||
|
||||
// 6) guarded!: named binding + mut arg visible outside + explicit drop
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
{
|
||||
let value = 6usize;
|
||||
let delta = 1usize;
|
||||
let sink_clone = sink.clone();
|
||||
|
||||
crate::guarded!(named => [mut value, delta] {
|
||||
sink_clone.store(value + delta, Ordering::SeqCst);
|
||||
});
|
||||
|
||||
*value += 10;
|
||||
assert_eq!(*value, 16);
|
||||
assert_eq!(*delta, 1);
|
||||
drop(named);
|
||||
}
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 17);
|
||||
|
||||
// 7) guarded!: unnamed statement + expression body + implicit drop at scope end
|
||||
let sink = Arc::new(AtomicUsize::new(0));
|
||||
{
|
||||
let n = 7usize;
|
||||
let sink_clone = sink.clone();
|
||||
crate::guarded!([n] sink_clone.store(n, Ordering::SeqCst));
|
||||
}
|
||||
assert_eq!(sink.load(Ordering::SeqCst), 7);
|
||||
|
||||
// 8) guarded!: explicit sync + panic path propagates on drop
|
||||
let dropped = catch_unwind(|| {
|
||||
guarded! {
|
||||
sync {
|
||||
panic!("matrix-boom");
|
||||
}
|
||||
}
|
||||
});
|
||||
assert!(dropped.is_err());
|
||||
|
||||
// 9) guarded!: async inference on drop detaches and executes
|
||||
let (tx, rx) = oneshot::channel();
|
||||
{
|
||||
let tx = Some(tx);
|
||||
crate::guarded!([mut tx] {
|
||||
let tx = tx.take();
|
||||
async move {
|
||||
if let Some(tx) = tx {
|
||||
let _ = tx.send(9usize);
|
||||
}
|
||||
}
|
||||
});
|
||||
}
|
||||
let detached = tokio::time::timeout(Duration::from_secs(1), rx)
|
||||
.await
|
||||
.expect("detached task should complete")
|
||||
.expect("detached task should send value");
|
||||
assert_eq!(detached, 9);
|
||||
}
|
||||
}
|
||||
Reference in New Issue
Block a user