From ca4bc057a9226a0901bfd37133b3deced47de13c Mon Sep 17 00:00:00 2001
From: Patrik Wenger <paddor@gmail.com>
Date: Fri, 22 May 2026 12:17:04 +0200
Subject: [PATCH] fix(driver): use Poller::notify() to wake poll backend from
 wakers

polling's Events::is_empty() filters NOTIFY_KEY events, so a
Poller::notify() wakeup produces an empty event set. Check the
AwakeFlag's NOTIFIED bit after wait() returns to detect this case
and return Ok(()) instead of ETIMEDOUT.

Fixes compio-rs/compio#928
---
 compio-driver/src/sys/driver/mod.rs      |  5 ++-
 compio-driver/src/sys/driver/poll/mod.rs | 13 +++---
 compio-runtime/Cargo.toml                |  7 +++
 compio-runtime/tests/waker.rs            | 54 ++++++++++++++++++++++++
 4 files changed, 71 insertions(+), 8 deletions(-)
 create mode 100644 compio-runtime/tests/waker.rs

diff --git a/compio-driver/src/sys/driver/mod.rs b/compio-driver/src/sys/driver/mod.rs
index 1a49becc..a138c605 100644
--- a/compio-driver/src/sys/driver/mod.rs
+++ b/compio-driver/src/sys/driver/mod.rs
@@ -43,8 +43,9 @@ impl AwakeFlag {
 
     /// Mark the driver as awake by overwriting the flag byte with `AWAKE`.
     /// This intentionally clears any previously set `NOTIFIED` flag.
-    pub fn set(&self) {
-        self.0.store(AWAKE, Ordering::Release);
+    /// Returns true if the `NOTIFIED` flag was set.
+    pub fn set(&self) -> bool {
+        (self.0.swap(AWAKE, Ordering::AcqRel) & NOTIFIED) != 0
     }
 
     /// Reset the flags. Returns true if it was notified.
diff --git a/compio-driver/src/sys/driver/poll/mod.rs b/compio-driver/src/sys/driver/poll/mod.rs
index 7d05a7b5..8344f5aa 100644
--- a/compio-driver/src/sys/driver/poll/mod.rs
+++ b/compio-driver/src/sys/driver/poll/mod.rs
@@ -450,13 +450,13 @@ impl Driver {
         if !need_wait || has_completed {
             timeout = Some(Duration::ZERO);
         }
-        // We need to poll the poller first to make sure it handles the internal notify
-        // event (if any).
         self.events.clear();
         self.notify.poll.wait(&mut self.events, timeout)?;
-        self.notify.set_awake();
+        // polling's Events::is_empty() filters NOTIFY_KEY events, so a
+        // Poller::notify() wakeup looks like an empty return.
+        let was_notified = self.notify.set_awake();
         if self.events.is_empty() {
-            if self.poll_completed() {
+            if was_notified | self.poll_completed() {
                 return Ok(());
             }
             if timeout_is_some {
@@ -544,6 +544,7 @@ impl Entry {
 }
 
 /// A notify handle to the inner driver.
+#[derive(Debug)]
 pub(crate) struct Notify {
     poll: Poller,
     awake: AwakeFlag,
@@ -557,8 +558,8 @@ impl Notify {
         }
     }
 
-    fn set_awake(&self) {
-        self.awake.set();
+    fn set_awake(&self) -> bool {
+        self.awake.set()
     }
 
     fn reset(&self) -> bool {
diff --git a/compio-runtime/Cargo.toml b/compio-runtime/Cargo.toml
index c875d199..2176e4b5 100644
--- a/compio-runtime/Cargo.toml
+++ b/compio-runtime/Cargo.toml
@@ -37,6 +37,9 @@ windows-sys = { workspace = true, features = ["Win32_System_IO"] }
 [target.'cfg(unix)'.dependencies]
 libc = { workspace = true }
 
+[dev-dependencies]
+flume = { workspace = true, features = ["async"] }
+
 [target.'cfg(windows)'.dev-dependencies]
 windows-sys = { workspace = true, features = ["Win32_UI_WindowsAndMessaging"] }
 
@@ -66,3 +69,7 @@ name = "event"
 [[test]]
 name = "drop"
 required-features = ["time"]
+
+[[test]]
+name = "waker"
+required-features = ["time"]
diff --git a/compio-runtime/tests/waker.rs b/compio-runtime/tests/waker.rs
new file mode 100644
index 00000000..ff445b59
--- /dev/null
+++ b/compio-runtime/tests/waker.rs
@@ -0,0 +1,54 @@
+use std::time::{Duration, Instant};
+
+use compio_runtime::ResumeUnwind;
+
+#[test]
+fn cross_thread_waker_interrupts_poll() {
+    let rt = compio_runtime::Runtime::new().unwrap();
+    rt.block_on(async {
+        let (tx, rx) = flume::bounded::<u32>(1);
+
+        let handle = compio_runtime::spawn(async move { rx.recv_async().await.unwrap() });
+
+        std::thread::spawn(move || {
+            std::thread::sleep(Duration::from_millis(10));
+            tx.send(42).unwrap();
+        });
+
+        let start = Instant::now();
+        let val = handle.await.resume_unwind().unwrap();
+        let elapsed = start.elapsed();
+
+        assert_eq!(val, 42);
+        assert!(
+            elapsed < Duration::from_millis(200),
+            "took {elapsed:?}, expected < 200ms"
+        );
+    });
+}
+
+#[test]
+fn same_thread_waker_schedules_promptly() {
+    let rt = compio_runtime::Runtime::new().unwrap();
+    rt.block_on(async {
+        let (tx, rx) = flume::bounded::<u32>(1);
+
+        compio_runtime::spawn(async move {
+            let val = rx.recv_async().await.unwrap();
+            assert_eq!(val, 42);
+        })
+        .detach();
+
+        compio_runtime::time::sleep(Duration::from_millis(10)).await;
+
+        let start = Instant::now();
+        tx.send(42).unwrap();
+        compio_runtime::time::sleep(Duration::from_millis(200)).await;
+        let elapsed = start.elapsed();
+
+        assert!(
+            elapsed < Duration::from_millis(400),
+            "took {elapsed:?}, expected < 400ms"
+        );
+    });
+}