Simplify process future by removing explicit channel, don't lock mutex as often

src/process.rs

@@ -1,5 +1,4 @@
 use actix_web::web::Bytes;
-use flume::r#async::RecvFut;
 use std::{
     ffi::OsStr,
     future::Future,
@@ -73,7 +72,7 @@ impl std::fmt::Debug for Process {
 }
 
 struct DropHandle {
-    inner: JoinHandle<()>,
+    inner: JoinHandle<std::io::Result<()>>,
 }
 
 struct ProcessReadState {
@@ -88,7 +87,6 @@ struct ProcessReadWaker {
 
 pub(crate) struct ProcessRead {
     inner: ChildStdout,
-    err_recv: RecvFut<'static, std::io::Error>,
     handle: DropHandle,
     closed: bool,
     state: Arc<ProcessReadState>,
@@ -233,9 +231,6 @@ impl Process {
         let stdin = child.stdin.take().expect("stdin exists");
         let stdout = child.stdout.take().expect("stdout exists");
 
-        let (tx, rx) = crate::sync::channel::<std::io::Error>(1);
-        let rx = rx.into_recv_async();
-
         let background_span =
             tracing::info_span!(parent: None, "Background process task", %command);
         background_span.follows_from(Span::current());
@@ -255,7 +250,7 @@ impl Process {
                 let error = match child_fut.with_timeout(timeout).await {
                     Ok(Ok(status)) if status.success() => {
                         guard.disarm();
-                        return;
+                        return Ok(());
                     }
                     Ok(Ok(status)) => {
                         std::io::Error::new(std::io::ErrorKind::Other, StatusError(status))
@@ -264,15 +259,15 @@ impl Process {
                     Err(_) => std::io::ErrorKind::TimedOut.into(),
                 };
 
-                let _ = tx.send(error);
-                let _ = child.kill().await;
+                child.kill().await?;
+
+                Err(error)
             }
             .instrument(background_span),
         );
 
         ProcessRead {
             inner: stdout,
-            err_recv: rx,
             handle: DropHandle { inner: handle },
             closed: false,
             state: ProcessReadState::new_woken(),
@@ -291,7 +286,7 @@ impl ProcessReadState {
 
     fn clone_parent(&self) -> Option<Waker> {
         let guard = self.parent.lock().unwrap();
-        guard.as_ref().map(|w| w.clone())
+        guard.as_ref().cloned()
     }
 
     fn into_parts(self) -> (AtomicU8, Option<Waker>) {
@@ -322,19 +317,26 @@ impl ProcessRead {
         }
     }
 
-    fn set_parent_waker(&self, parent: &Waker) {
+    fn set_parent_waker(&self, parent: &Waker) -> bool {
         let mut guard = self.state.parent.lock().unwrap();
         if let Some(waker) = guard.as_mut() {
             if !waker.will_wake(parent) {
                 *waker = parent.clone();
+                true
+            } else {
+                false
             }
         } else {
             *guard = Some(parent.clone());
+            true
         }
     }
+
+    fn mark_all_woken(&self) {
+        self.state.flags.store(0xff, Ordering::Release);
+    }
 }
 
-const RECV_WAKER: u8 = 0b_0010;
 const HANDLE_WAKER: u8 = 0b_0100;
 
 impl AsyncRead for ProcessRead {
@@ -343,8 +345,6 @@ impl AsyncRead for ProcessRead {
         cx: &mut Context<'_>,
         buf: &mut ReadBuf<'_>,
     ) -> Poll<std::io::Result<()>> {
-        self.set_parent_waker(cx.waker());
-
         let span = self.span.clone();
         let guard = span.enter();
 
@@ -364,29 +364,30 @@ impl AsyncRead for ProcessRead {
                 } else {
                     break Poll::Ready(Ok(()));
                 }
-            } else if let Some(waker) = self.get_waker(RECV_WAKER) {
-                // only poll recv if we've been explicitly woken
-                let mut recv_cx = Context::from_waker(&waker);
-
-                if let Poll::Ready(res) = Pin::new(&mut self.err_recv).poll(&mut recv_cx) {
-                    if let Ok(err) = res {
-                        self.closed = true;
-                        break Poll::Ready(Err(err));
-                    }
-                }
             } else if let Some(waker) = self.get_waker(HANDLE_WAKER) {
                 // only poll handle if we've been explicitly woken
                 let mut handle_cx = Context::from_waker(&waker);
 
                 if let Poll::Ready(res) = Pin::new(&mut self.handle.inner).poll(&mut handle_cx) {
-                    if let Err(e) = res {
+                    let error = match res {
+                        Ok(Ok(())) => continue,
+                        Ok(Err(e)) => e,
+                        Err(e) => std::io::Error::new(std::io::ErrorKind::Other, e),
+                    };
+
                     self.closed = true;
-                        break Poll::Ready(Err(std::io::Error::new(std::io::ErrorKind::Other, e)));
-                    }
+                    break Poll::Ready(Err(error));
                 }
             } else if self.closed {
+                // Stop if we're closed
                 break Poll::Ready(Ok(()));
+            } else if self.set_parent_waker(cx.waker()) {
+                // if we updated the stored waker, mark all as woken an try polling again
+                // This doesn't actually "wake" the waker, it just allows the handle to be polled
+                // again next iteration
+                self.mark_all_woken();
             } else {
+                // if the waker hasn't changed and nothing polled ready, return pending
                 break Poll::Pending;
             }
         };