Fix concurrent accepts (#2403)

cli/resources.rs

@@ -171,12 +171,49 @@ impl Resource {
     }
   }
 
+  /// Track the current task (for TcpListener resource).
+  /// Throws an error if another task is already tracked.
+  pub fn track_task(&mut self) -> Result<(), std::io::Error> {
+    let mut table = RESOURCE_TABLE.lock().unwrap();
+    // Only track if is TcpListener.
+    if let Some(Repr::TcpListener(_, t)) = table.get_mut(&self.rid) {
+      // Currently, we only allow tracking a single accept task for a listener.
+      // This might be changed in the future with multiple workers.
+      // Caveat: TcpListener by itself also only tracks an accept task at a time.
+      // See https://github.com/tokio-rs/tokio/issues/846#issuecomment-454208883
+      if t.is_some() {
+        return Err(std::io::Error::new(
+          std::io::ErrorKind::Other,
+          "Another accept task is ongoing",
+        ));
+      }
+      t.replace(futures::task::current());
+    }
+    Ok(())
+  }
+
+  /// Stop tracking a task (for TcpListener resource).
+  /// Happens when the task is done and thus no further tracking is needed.
+  pub fn untrack_task(&mut self) {
+    let mut table = RESOURCE_TABLE.lock().unwrap();
+    // Only untrack if is TcpListener.
+    if let Some(Repr::TcpListener(_, t)) = table.get_mut(&self.rid) {
+      if t.is_some() {
+        t.take();
+      }
+    }
+  }
+
   // close(2) is done by dropping the value. Therefore we just need to remove
   // the resource from the RESOURCE_TABLE.
   pub fn close(&self) {
     let mut table = RESOURCE_TABLE.lock().unwrap();
-    let r = table.remove(&self.rid);
-    assert!(r.is_some());
+    let r = table.remove(&self.rid).unwrap();
+    // If TcpListener, we must kill all pending accepts!
+    if let Repr::TcpListener(_, Some(t)) = r {
+      // Call notify on the tracked task, so that they would error out.
+      t.notify();
+    }
   }
 
   pub fn shutdown(&mut self, how: Shutdown) -> Result<(), DenoError> {

cli/tokio_util.rs

@@ -78,14 +78,31 @@ pub fn accept(r: Resource) -> Accept {
 pub struct Accept {
   state: AcceptState,
 }
-
 impl Future for Accept {
   type Item = (TcpStream, SocketAddr);
   type Error = io::Error;
 
   fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
     let (stream, addr) = match self.state {
-      AcceptState::Pending(ref mut r) => try_ready!(r.poll_accept()),
+      // Similar to try_ready!, but also track/untrack accept task
+      // in TcpListener resource.
+      // In this way, when the listener is closed, the task can be
+      // notified to error out (instead of stuck forever).
+      AcceptState::Pending(ref mut r) => match r.poll_accept() {
+        Ok(futures::prelude::Async::Ready(t)) => {
+          r.untrack_task();
+          t
+        }
+        Ok(futures::prelude::Async::NotReady) => {
+          // Would error out if another accept task is being tracked.
+          r.track_task()?;
+          return Ok(futures::prelude::Async::NotReady);
+        }
+        Err(e) => {
+          r.untrack_task();
+          return Err(e);
+        }
+      },
       AcceptState::Empty => panic!("poll Accept after it's done"),
     };
 

js/net_test.ts

@@ -21,7 +21,6 @@ testPerm({ net: true }, async function netCloseWhileAccept(): Promise<void> {
   assertEquals(err.message, "Listener has been closed");
 });
 
-/* TODO(ry) Re-enable this test.
 testPerm({ net: true }, async function netConcurrentAccept(): Promise<void> {
   const listener = Deno.listen("tcp", ":4502");
   let acceptErrCount = 0;
@@ -42,7 +41,6 @@ testPerm({ net: true }, async function netConcurrentAccept(): Promise<void> {
   await [p, p1];
   assertEquals(acceptErrCount, 1);
 });
-*/
 
 testPerm({ net: true }, async function netDialListen(): Promise<void> {
   const listener = Deno.listen("tcp", ":4500");