Make boot_time::timeout() timeout immediately when passing zero duration

It's possible that the duration returned by Quiche timeout()
is Duration::ZERO. However, boot_time::sleep(Duration::ZERO).await
doesn't wake up immediately in tokio::select. This results in
missing one Quiche on_timeout() call.

Bug: 223356608
Test: cd packages/modules/DnsResolver && atest
Change-Id: Ib9d7fc9792158262d87a86f4e474e618efdbf408

1 files changed, 16 insertions, 0 deletions

diff --git a/doh/boot_time.rs b/doh/boot_time.rs
index 1f6f97df..ff7462cf 100644
--- a/doh/boot_time.rs
+++ b/doh/boot_time.rs
@@ -123,6 +123,7 @@ impl TimerFd {
     }
 
     fn set(&self, duration: Duration) {
+        assert_ne!(duration, Duration::from_millis(0));
         let timer = libc::itimerspec {
             it_interval: libc::timespec { tv_sec: 0, tv_nsec: 0 },
             it_value: libc::timespec {
@@ -147,6 +148,13 @@ pub async fn timeout<T>(duration: Duration, future: impl Future<Output = T>) ->
     // Ideally, all timeouts in a runtime would share a timerfd. That will be much more
     // straightforwards to implement when moving this functionality into `tokio`.
 
+    // According to timerfd_settime(), setting zero duration will disarm the timer, so
+    // we return immediate timeout here.
+    // Can't use is_zero() for now because sc-mainline-prod's Rust version is below 1.53.
+    if duration == Duration::from_millis(0) {
+        return Err(Elapsed(()));
+    }
+
     // The failure conditions for this are rare (see `man 2 timerfd_create`) and the caller would
     // not be able to do much in response to them. When integrated into tokio, this would be called
     // during runtime setup.
@@ -204,3 +212,11 @@ async fn timeout_drift() {
         assert!(drift < Duration::from_millis(5));
     }
 }
+
+#[tokio::test]
+async fn timeout_duration_zero() {
+    let start = BootTime::now();
+    assert!(timeout(Duration::from_millis(0), pending::<()>()).await.is_err());
+    let taken = start.elapsed();
+    assert!(taken < Duration::from_millis(5));
+}