Track last error atomically

Eliminate the need for UdpSocket to be passed mutably into send_mmsg().

src/lib.rs

@@ -2,10 +2,10 @@
 use std::{
     net::{IpAddr, Ipv6Addr, SocketAddr},
     sync::atomic::{AtomicUsize, Ordering},
-    time::{Duration, Instant},
 };
 
 pub use crate::cmsg::{AsPtr, EcnCodepoint, Source, Transmit};
+use imp::LastSendError;
 use tracing::warn;
 
 mod cmsg;
@@ -94,20 +94,18 @@ impl Default for RecvMeta {
 }
 
 /// Log at most 1 IO error per minute
-const IO_ERROR_LOG_INTERVAL: Duration = std::time::Duration::from_secs(60);
+const IO_ERROR_LOG_INTERVAL: u64 = 60;
 
 /// Logs a warning message when sendmsg fails
 ///
 /// Logging will only be performed if at least [`IO_ERROR_LOG_INTERVAL`]
 /// has elapsed since the last error was logged.
 fn log_sendmsg_error<B: AsPtr<u8>>(
-    last_send_error: &mut Instant,
+    last_send_error: LastSendError,
     err: impl core::fmt::Debug,
     transmit: &Transmit<B>,
 ) {
-    let now = Instant::now();
-    if now.saturating_duration_since(*last_send_error) > IO_ERROR_LOG_INTERVAL {
-        *last_send_error = now;
+    if last_send_error.should_log() {
         warn!(
         "sendmsg error: {:?}, Transmit: {{ destination: {:?}, src_ip: {:?}, enc: {:?}, len: {:?}, segment_size: {:?} }}",
             err, transmit.dst, transmit.src, transmit.ecn, transmit.contents.len(), transmit.segment_size);

src/unix.rs

@@ -4,9 +4,12 @@ use std::{
     mem::{self, MaybeUninit},
     net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr, SocketAddrV4, SocketAddrV6},
     os::{fd::AsFd, unix::io::AsRawFd},
-    sync::atomic::AtomicUsize,
+    sync::{
+        atomic::{AtomicU64, AtomicUsize, Ordering},
+        Arc,
+    },
     task::{Context, Poll},
-    time::Instant,
+    time::SystemTime,
 };
 
 use crate::cmsg::{AsPtr, EcnCodepoint, Source, Transmit};
@@ -31,7 +34,7 @@ type IpTosTy = libc::c_int;
 #[derive(Debug)]
 pub struct UdpSocket {
     io: tokio::net::UdpSocket,
-    last_send_error: Instant,
+    last_send_error: LastSendError,
 }
 
 impl AsRawFd for UdpSocket {
@@ -46,16 +49,51 @@ impl AsFd for UdpSocket {
     }
 }
 
+#[derive(Clone, Debug)]
+pub(crate) struct LastSendError(Arc<AtomicU64>);
+
+impl Default for LastSendError {
+    fn default() -> Self {
+        let now = Self::now();
+        Self(Arc::new(AtomicU64::new(
+            now.checked_sub(2 * IO_ERROR_LOG_INTERVAL).unwrap_or(now),
+        )))
+    }
+}
+
+impl LastSendError {
+    fn now() -> u64 {
+        SystemTime::now()
+            .duration_since(SystemTime::UNIX_EPOCH)
+            .unwrap()
+            .as_secs()
+    }
+
+    /// Determine whether the last error was more than `IO_ERROR_LOG_INTERVAL`
+    /// seconds ago. If so, update the last error time and return true.
+    ///
+    /// Note: if the system clock regresses more tha `IO_ERROR_LOG_INTERVAL`,
+    /// this function may impose an additional delay on log message emission.
+    /// Similarly, if it advances, messages may be emitted prematurely.
+    pub(crate) fn should_log(&self) -> bool {
+        let now = Self::now();
+        self.0
+            .fetch_update(Ordering::SeqCst, Ordering::SeqCst, |cur| {
+                (now.saturating_sub(cur) > IO_ERROR_LOG_INTERVAL).then_some(now)
+            })
+            .is_ok()
+    }
+}
+
 impl UdpSocket {
     /// Creates a new UDP socket from a previously created `std::net::UdpSocket`
     pub fn from_std(socket: std::net::UdpSocket) -> io::Result<UdpSocket> {
         socket.set_nonblocking(true)?;
 
         init(SockRef::from(&socket))?;
-        let now = Instant::now();
         Ok(UdpSocket {
             io: tokio::net::UdpSocket::from_std(socket)?,
-            last_send_error: now.checked_sub(2 * IO_ERROR_LOG_INTERVAL).unwrap_or(now),
+            last_send_error: LastSendError::default(),
         })
     }
 
@@ -67,10 +105,9 @@ impl UdpSocket {
     pub async fn bind<A: ToSocketAddrs>(addr: A) -> io::Result<UdpSocket> {
         let io = tokio::net::UdpSocket::bind(addr).await?;
         init(SockRef::from(&io))?;
-        let now = Instant::now();
         Ok(UdpSocket {
             io,
-            last_send_error: now.checked_sub(2 * IO_ERROR_LOG_INTERVAL).unwrap_or(now),
+            last_send_error: LastSendError::default(),
         })
     }
 
@@ -195,13 +232,13 @@ impl UdpSocket {
     ///
     /// [`sendmmsg`]: https://linux.die.net/man/2/sendmmsg
     pub async fn send_mmsg<B: AsPtr<u8>>(
-        &mut self,
+        &self,
         state: &UdpState,
         transmits: &[Transmit<B>],
     ) -> Result<usize, io::Error> {
         let n = loop {
             self.io.writable().await?;
-            let last_send_error = &mut self.last_send_error;
+            let last_send_error = self.last_send_error.clone();
             let io = &self.io;
             match io.try_io(Interest::WRITABLE, || {
                 send(state, SockRef::from(io), last_send_error, transmits)
@@ -278,11 +315,15 @@ impl UdpSocket {
         transmits: &[Transmit<B>],
     ) -> Poll<io::Result<usize>> {
         loop {
-            let last_send_error = &mut self.last_send_error;
             ready!(self.io.poll_send_ready(cx))?;
             let io = &self.io;
             if let Ok(res) = io.try_io(Interest::WRITABLE, || {
-                send(state, SockRef::from(io), last_send_error, transmits)
+                send(
+                    state,
+                    SockRef::from(io),
+                    self.last_send_error.clone(),
+                    transmits,
+                )
             }) {
                 return Poll::Ready(Ok(res));
             }
@@ -353,7 +394,7 @@ pub mod sync {
     #[derive(Debug)]
     pub struct UdpSocket {
         io: std::net::UdpSocket,
-        last_send_error: Instant,
+        last_send_error: LastSendError,
     }
 
     impl AsRawFd for UdpSocket {
@@ -372,21 +413,19 @@ pub mod sync {
         pub fn from_std(socket: std::net::UdpSocket) -> io::Result<Self> {
             init(SockRef::from(&socket))?;
             socket.set_nonblocking(false)?;
-            let now = Instant::now();
             Ok(Self {
                 io: socket,
-                last_send_error: now.checked_sub(2 * IO_ERROR_LOG_INTERVAL).unwrap_or(now),
+                last_send_error: LastSendError::default(),
             })
         }
         /// create a new UDP socket and attempt to bind to `addr`
         pub fn bind<A: std::net::ToSocketAddrs>(addr: A) -> io::Result<Self> {
             let io = std::net::UdpSocket::bind(addr)?;
             init(SockRef::from(&io))?;
             io.set_nonblocking(false)?;
-            let now = Instant::now();
             Ok(Self {
                 io,
-                last_send_error: now.checked_sub(2 * IO_ERROR_LOG_INTERVAL).unwrap_or(now),
+                last_send_error: LastSendError::default(),
             })
         }
         /// sets nonblocking mode
@@ -474,7 +513,7 @@ pub mod sync {
             send(
                 state,
                 SockRef::from(&self.io),
-                &mut self.last_send_error,
+                self.last_send_error.clone(),
                 transmits,
             )
         }
@@ -681,7 +720,7 @@ fn send_msg<B: AsPtr<u8>>(
 fn send<B: AsPtr<u8>>(
     state: &UdpState,
     io: SockRef<'_>,
-    last_send_error: &mut Instant,
+    last_send_error: LastSendError,
     transmits: &[Transmit<B>],
 ) -> io::Result<usize> {
     use std::ptr;
@@ -802,7 +841,7 @@ fn send_msg<B: AsPtr<u8>>(
 fn send<B: AsPtr<u8>>(
     _state: &UdpState,
     io: SockRef<'_>,
-    last_send_error: &mut Instant,
+    last_send_error: LastSendError,
     transmits: &[Transmit<B>],
 ) -> io::Result<usize> {
     let mut hdr: libc::msghdr = unsafe { mem::zeroed() };
@@ -828,7 +867,7 @@ fn send<B: AsPtr<u8>>(
                     //   Those are not fatal errors, since the
                     //   configuration can be dynamically changed.
                     // - Destination unreachable errors have been observed for other
-                    log_sendmsg_error(last_send_error, e, &transmits[sent]);
+                    log_sendmsg_error(last_send_error.clone(), e, &transmits[sent]);
                     sent += 1;
                 }
             }