fix: drop mutex guard when DuplexStream I/O op is pending

Cargo.toml

@@ -7,9 +7,9 @@ license = "MIT"
 repository = "https://github.com/SteveLauC/monoio-duplex"
 
 [dependencies]
-async-lock = "3.4.0"
 bytes = "1.7.2"
 monoio = "0.2.4"
 futures = "0.3.31"
 
 [dev-dependencies]
+tokio = { version = "1.41.0", features = ["sync"] }

src/duplex.rs

@@ -2,10 +2,11 @@
 
 use super::simplex::SimplexStream;
 
-use async_lock::Mutex;
+use futures::FutureExt;
 use monoio::io::AsyncReadRent;
 use monoio::io::AsyncWriteRent;
 use std::rc::Rc;
+use std::sync::Mutex;
 
 /// Create a new pair of `DuplexStream`s that act like a pair of connected sockets.
 ///
@@ -78,48 +79,90 @@ pub struct DuplexStream {
 
 impl Drop for DuplexStream {
     fn drop(&mut self) {
-        futures::executor::block_on(async {
-            // notify the other side of the closure
-            self.write.lock().await.close_write();
-            self.read.lock().await.close_read();
-        })
+        // notify the other side of the closure
+        self.write.lock().unwrap().close_write();
+        self.read.lock().unwrap().close_read();
     }
 }
 
+/// A helper macro to `.await` the I/O function, used in our I/O traits
+/// implementations.
+///
+/// Different from a plain `function().await`, it drops the lock guard if future
+/// `function()` is pending.
+macro_rules! await_io_future {
+    // For functions that do not have arugments: flush/shutdown
+    ($trait:ident, $function:ident, $guard:expr) => {{
+        let opt_read_ready = <SimplexStream as $trait>::$function(&mut *$guard).now_or_never();
+
+        match opt_read_ready {
+            Some(result) => result,
+            None => {
+                // drop the Mutex guard or it could deadlock
+                // https://github.com/SteveLauC/monoio-duplex/issues/7
+                drop($guard);
+                std::future::pending().await
+            }
+        }
+    }};
+
+    // For functions with a `buf` arugment: read/readv/write/writev
+    ($trait:ident, $function:ident, $guard:expr, $buf:expr) => {{
+        let opt_read_ready =
+            <SimplexStream as $trait>::$function(&mut *$guard, $buf).now_or_never();
+
+        match opt_read_ready {
+            Some(result) => result,
+            None => {
+                // drop the Mutex guard or it could deadlock
+                // https://github.com/SteveLauC/monoio-duplex/issues/7
+                drop($guard);
+                std::future::pending().await
+            }
+        }
+    }};
+}
+
 impl AsyncReadRent for DuplexStream {
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn read<T: monoio::buf::IoBufMut>(&mut self, buf: T) -> monoio::BufResult<usize, T> {
-        let mut read_simplex = self.read.lock().await;
-        <SimplexStream as AsyncReadRent>::read(&mut *read_simplex, buf).await
+        let mut read_simplex = self.read.lock().unwrap();
+        await_io_future!(AsyncReadRent, read, read_simplex, buf)
     }
 
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn readv<T: monoio::buf::IoVecBufMut>(&mut self, buf: T) -> monoio::BufResult<usize, T> {
-        let mut read_simplex = self.read.lock().await;
-        <SimplexStream as AsyncReadRent>::readv(&mut *read_simplex, buf).await
+        let mut read_simplex = self.read.lock().unwrap();
+        await_io_future!(AsyncReadRent, readv, read_simplex, buf)
     }
 }
 
 impl AsyncWriteRent for DuplexStream {
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn write<T: monoio::buf::IoBuf>(&mut self, buf: T) -> monoio::BufResult<usize, T> {
-        let mut write_simplex = self.write.lock().await;
-        <SimplexStream as AsyncWriteRent>::write(&mut *write_simplex, buf).await
+        let mut write_simplex = self.write.lock().unwrap();
+        await_io_future!(AsyncWriteRent, write, write_simplex, buf)
     }
 
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn writev<T: monoio::buf::IoVecBuf>(
         &mut self,
         buf_vec: T,
     ) -> monoio::BufResult<usize, T> {
-        let mut write_simplex = self.write.lock().await;
-        <SimplexStream as AsyncWriteRent>::writev(&mut *write_simplex, buf_vec).await
+        let mut write_simplex = self.write.lock().unwrap();
+        await_io_future!(AsyncWriteRent, writev, write_simplex, buf_vec)
     }
 
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn flush(&mut self) -> std::io::Result<()> {
-        let mut write_simplex = self.write.lock().await;
-        <SimplexStream as AsyncWriteRent>::flush(&mut *write_simplex).await
+        let mut write_simplex = self.write.lock().unwrap();
+        await_io_future!(AsyncWriteRent, flush, write_simplex)
     }
 
+    #[allow(clippy::await_holding_lock)] // false-positive, we explicitly dropped the guard before the await point.
     async fn shutdown(&mut self) -> std::io::Result<()> {
-        let mut write_simplex = self.write.lock().await;
-        <SimplexStream as AsyncWriteRent>::shutdown(&mut *write_simplex).await
+        let mut write_simplex = self.write.lock().unwrap();
+        await_io_future!(AsyncWriteRent, shutdown, write_simplex)
     }
 }
 
@@ -180,4 +223,42 @@ mod tests {
             std::io::ErrorKind::BrokenPipe
         );
     }
+
+    #[monoio::test(enable_timer = true)]
+    async fn pending_read_will_not_hold_mutex_gaurd() {
+        let (mut client, server) = duplex(100);
+        let (tx, rx) = tokio::sync::oneshot::channel::<()>();
+
+        monoio::spawn(async move {
+            // send task start signal
+            tx.send(()).unwrap();
+            // this line should block
+            let (_result, _buf) = client.read(vec![0_u8; 10]).await;
+        });
+
+        rx.await.unwrap();
+
+        drop(server);
+    }
+
+    #[monoio::test(enable_timer = true)]
+    async fn pending_write_will_not_hold_mutex_gaurd() {
+        let (mut client, server) = duplex(10);
+        let (tx, rx) = tokio::sync::oneshot::channel::<()>();
+
+        // write 10 bytes to make future writes pending
+        let (write_result, _buf) = client.write(vec![0_u8; 10]).await;
+        assert_eq!(write_result.unwrap(), 10);
+
+        monoio::spawn(async move {
+            // send task start signal
+            tx.send(()).unwrap();
+            // this line should block
+            let (_result, _buf) = client.write(vec![0_u8; 10]).await;
+        });
+
+        rx.await.unwrap();
+
+        drop(server);
+    }
 }