io: make copy cooperative

tokio/src/io/util/copy.rs

@@ -82,6 +82,19 @@ impl CopyBuffer {
         R: AsyncRead + ?Sized,
         W: AsyncWrite + ?Sized,
     {
+        ready!(crate::trace::trace_leaf(cx));
+        #[cfg(any(
+            feature = "fs",
+            feature = "io-std",
+            feature = "net",
+            feature = "process",
+            feature = "rt",
+            feature = "signal",
+            feature = "sync",
+            feature = "time",
+        ))]
+        // Keep track of task budget
+        let coop = ready!(crate::runtime::coop::poll_proceed(cx));
         loop {
             // If our buffer is empty, then we need to read some data to
             // continue.
@@ -90,13 +103,49 @@ impl CopyBuffer {
                 self.cap = 0;
 
                 match self.poll_fill_buf(cx, reader.as_mut()) {
-                    Poll::Ready(Ok(())) => (),
-                    Poll::Ready(Err(err)) => return Poll::Ready(Err(err)),
+                    Poll::Ready(Ok(())) => {
+                        #[cfg(any(
+                            feature = "fs",
+                            feature = "io-std",
+                            feature = "net",
+                            feature = "process",
+                            feature = "rt",
+                            feature = "signal",
+                            feature = "sync",
+                            feature = "time",
+                        ))]
+                        coop.made_progress();
+                    }
+                    Poll::Ready(Err(err)) => {
+                        #[cfg(any(
+                            feature = "fs",
+                            feature = "io-std",
+                            feature = "net",
+                            feature = "process",
+                            feature = "rt",
+                            feature = "signal",
+                            feature = "sync",
+                            feature = "time",
+                        ))]
+                        coop.made_progress();
+                        return Poll::Ready(Err(err));
+                    }
                     Poll::Pending => {
                         // Try flushing when the reader has no progress to avoid deadlock
                         // when the reader depends on buffered writer.
                         if self.need_flush {
                             ready!(writer.as_mut().poll_flush(cx))?;
+                            #[cfg(any(
+                                feature = "fs",
+                                feature = "io-std",
+                                feature = "net",
+                                feature = "process",
+                                feature = "rt",
+                                feature = "signal",
+                                feature = "sync",
+                                feature = "time",
+                            ))]
+                            coop.made_progress();
                             self.need_flush = false;
                         }
 
@@ -108,6 +157,17 @@ impl CopyBuffer {
             // If our buffer has some data, let's write it out!
             while self.pos < self.cap {
                 let i = ready!(self.poll_write_buf(cx, reader.as_mut(), writer.as_mut()))?;
+                #[cfg(any(
+                    feature = "fs",
+                    feature = "io-std",
+                    feature = "net",
+                    feature = "process",
+                    feature = "rt",
+                    feature = "signal",
+                    feature = "sync",
+                    feature = "time",
+                ))]
+                coop.made_progress();
                 if i == 0 {
                     return Poll::Ready(Err(io::Error::new(
                         io::ErrorKind::WriteZero,
@@ -132,6 +192,17 @@ impl CopyBuffer {
             // data and finish the transfer.
             if self.pos == self.cap && self.read_done {
                 ready!(writer.as_mut().poll_flush(cx))?;
+                #[cfg(any(
+                    feature = "fs",
+                    feature = "io-std",
+                    feature = "net",
+                    feature = "process",
+                    feature = "rt",
+                    feature = "signal",
+                    feature = "sync",
+                    feature = "time",
+                ))]
+                coop.made_progress();
                 return Poll::Ready(Ok(self.amt));
             }
         }

tokio/tests/io_copy.rs

@@ -85,3 +85,18 @@ async fn proxy() {
 
     assert_eq!(n, 1024);
 }
+
+#[tokio::test]
+async fn copy_is_cooperative() {
+    tokio::select! {
+        biased;
+        _ = async {
+            loop {
+                let mut reader: &[u8] = b"hello";
+                let mut writer: Vec<u8> = vec![];
+                let _ = io::copy(&mut reader, &mut writer).await;
+            }
+        } => {},
+        _ = tokio::task::yield_now() => {}
+    }
+}

tokio/tests/io_copy_bidirectional.rs

@@ -138,3 +138,28 @@ async fn immediate_exit_on_read_error() {
 
     assert!(copy_bidirectional(&mut a, &mut b).await.is_err());
 }
+
+#[tokio::test]
+async fn copy_bidirectional_is_cooperative() {
+    tokio::select! {
+        biased;
+        _ = async {
+            loop {
+                let payload = b"here, take this";
+
+                let mut a = tokio_test::io::Builder::new()
+                    .read(payload)
+                    .write(payload)
+                    .build();
+
+                let mut b = tokio_test::io::Builder::new()
+                    .read(payload)
+                    .write(payload)
+                    .build();
+
+                let _ = copy_bidirectional(&mut a, &mut b).await;
+            }
+        } => {},
+        _ = tokio::task::yield_now() => {}
+    }
+}