Add wait_until_or_cancelled API to WaitQueue

framework/aster-frame/src/sync/wait.rs

@@ -29,10 +29,10 @@ impl WaitQueue {
     /// Wait until some condition becomes true.
     ///
     /// This method takes a closure that tests a user-given condition.
-    /// The method only returns if the condition returns Some(_).
-    /// A waker thread should first make the condition Some(_), then invoke the
+    /// The method only returns if the condition returns `Some(_)`.
+    /// A waker thread should first make the condition `Some(_)`, then invoke the
     /// `wake`-family method. This ordering is important to ensure that waiter
-    /// threads do not lose any wakeup notifiations.
+    /// threads do not lose any wakeup notifications.
     ///
     /// By taking a condition closure, his wait-wakeup mechanism becomes
     /// more efficient and robust.
@@ -44,36 +44,43 @@ impl WaitQueue {
             return res;
         }
 
-        let (waiter, waker) = Waiter::new_pair();
+        let (waiter, _) = Waiter::new_pair();
 
-        loop {
-            // Enqueue the waker before checking `cond()` to avoid races
-            self.enqueue(waker.clone());
-
-            if let Some(res) = cond() {
-                return res;
-            };
-            waiter.wait();
-        }
+        self.wait_until_or_cancelled(cond, waiter, || false)
+            .unwrap()
     }
 
-    pub fn wait_until_or_cancelled<F, R>(&self, mut cond: F) -> R
+    /// Wait until some condition becomes true or the cancel condition becomes true.
+    ///
+    /// This method will return `Some(_)` if the condition returns `Some(_)`, and will return
+    /// the condition test result regardless what it is when the cancel condition becomes true.
+    #[doc(hidden)]
+    pub fn wait_until_or_cancelled<F, R, FCancel>(
+        &self,
+        mut cond: F,
+        waiter: Waiter,
+        cancel_cond: FCancel,
+    ) -> Option<R>
     where
         F: FnMut() -> Option<R>,
+        FCancel: Fn() -> bool,
     {
-        if let Some(res) = cond() {
-            return res;
-        }
-
-        let (waiter, waker) = Waiter::new_pair();
+        let waker = waiter.waker();
 
         loop {
             // Enqueue the waker before checking `cond()` to avoid races
             self.enqueue(waker.clone());
 
             if let Some(res) = cond() {
-                return res;
+                return Some(res);
             };
+
+            if cancel_cond() {
+                // Drop the waiter and check again to avoid missing a wake event.
+                drop(waiter);
+                return cond();
+            }
+
             waiter.wait();
         }
     }
@@ -120,6 +127,7 @@ impl WaitQueue {
         }
     }
 
+    /// Return whether the current wait queue is empty.
     pub fn is_empty(&self) -> bool {
         self.num_wakers.load(Ordering::Acquire) == 0
     }
@@ -174,6 +182,11 @@ impl Waiter {
     pub fn wait(&self) {
         self.waker.do_wait();
     }
+
+    /// Gets the associated [`Waker`] of the current waiter.
+    pub fn waker(&self) -> Arc<Waker> {
+        self.waker.clone()
+    }
 }
 
 impl Drop for Waiter {
@@ -237,9 +250,3 @@ impl Waker {
         self.has_woken.store(true, Ordering::Release);
     }
 }
-
-impl Default for Waiter {
-    fn default() -> Self {
-        Self::new()
-    }
-}

framework/aster-frame/src/vm/kspace.rs

@@ -6,6 +6,7 @@ use core::ops::Range;
 
 use align_ext::AlignExt;
 use spin::Once;
+use static_assertions::const_assert;
 
 use super::{
     page_table::{nr_ptes_per_node, KernelMode, PageTable},

kernel/aster-nix/src/prelude.rs

@@ -44,7 +44,7 @@ pub(crate) use crate::{
     current, current_thread,
     error::{Errno, Error},
     print, println,
-    time::Clock,
+    time::{wait::WaitTimeout, Clock},
 };
 pub(crate) type Result<T> = core::result::Result<T, Error>;
 pub(crate) use crate::{return_errno, return_errno_with_message};

kernel/aster-nix/src/time/wait.rs

@@ -1,13 +1,12 @@
 // SPDX-License-Identifier: MPL-2.0
 
-use alloc::sync::Arc;
 use core::time::Duration;
 
-use aster_frame::sync::{WaitQueue, Waiter, Waker};
+use aster_frame::sync::{WaitQueue, Waiter};
 
-use super::clock::JIFFIES_TIMER_MANAGER;
+use super::clocks::JIFFIES_TIMER_MANAGER;
 
-/// A trait that provide the timeout related function for WaitQueue.
+/// A trait that provide the timeout related function for [`WaitQueue`]`.
 pub trait WaitTimeout {
     /// Wait until some condition returns `Some(_)`, or a given timeout is reached. If
     /// the condition does not becomes `Some(_)` before the timeout is reached, the
@@ -22,36 +21,32 @@ impl WaitTimeout for WaitQueue {
     where
         F: FnMut() -> Option<R>,
     {
+        if *timeout == Duration::ZERO {
+            return cond();
+        }
+
         if let Some(res) = cond() {
             return Some(res);
         }
 
         let (waiter, waker) = Waiter::new_pair();
-        let wake_up = {
-            let waker = waker.clone();
-            move || {
-                waker.wake_up();
-            }
-        };
 
-        let jiffies_timer = JIFFIES_TIMER_MANAGER.get().unwrap().create_timer(wake_up);
+        let jiffies_timer = JIFFIES_TIMER_MANAGER.get().unwrap().create_timer(move || {
+            waker.wake_up();
+        });
         jiffies_timer.set_timeout(*timeout);
 
-        loop {
-            // Enqueue the waker before checking `cond()` to avoid races
-            self.enqueue(waker.clone());
-
-            if let Some(res) = cond() {
-                jiffies_timer.clear();
-                return Some(res);
+        let cancel_cond = {
+            let jiffies_timer = jiffies_timer.clone();
+            move || jiffies_timer.remain() == Duration::ZERO
         };
+        let res = self.wait_until_or_cancelled(cond, waiter, cancel_cond);
 
-            if jiffies_timer.remain() == Duration::ZERO {
-                drop(waiter);
-                return cond();
+        // If res is `Some`, then the timeout may not have been expired. We cancel it manually.
+        if res.is_some() {
+            jiffies_timer.cancel();
         }
 
-            waiter.wait();
-        }
+        res
     }
 }