runtime/comms: limited concurrent connections to 1 only.

src/runtime/src/comms.rs

@@ -18,6 +18,8 @@ use libboard_zynq::{
     },
     timer::GlobalTimer,
 };
+use libcortex_a9::sync_channel;
+use futures::{select_biased, future::FutureExt};
 use libasync::{smoltcp::{Sockets, TcpStream}, task};
 
 use crate::config;
@@ -230,10 +232,10 @@ async fn handle_run_kernel(stream: Option<&TcpStream>, control: &Rc<RefCell<kern
 }
 
 
-async fn load_kernel(buffer: Vec<u8>, control: &Rc<RefCell<kernel::Control>>, stream: Option<&TcpStream>) -> Result<()> {
+async fn load_kernel(buffer: &Vec<u8>, control: &Rc<RefCell<kernel::Control>>, stream: Option<&TcpStream>) -> Result<()> {
     let mut control = control.borrow_mut();
     control.restart();
-    control.tx.async_send(kernel::Message::LoadRequest(buffer)).await;
+    control.tx.async_send(kernel::Message::LoadRequest(buffer.to_vec())).await;
     let reply = control.rx.async_recv().await;
     match reply {
         kernel::Message::LoadCompleted => {
@@ -279,7 +281,7 @@ async fn handle_connection(stream: &TcpStream, control: Rc<RefCell<kernel::Contr
             },
             Request::LoadKernel => {
                 let buffer = read_bytes(stream, 1024*1024).await?;
-                load_kernel(buffer, &control, Some(stream)).await?;
+                load_kernel(&buffer, &control, Some(stream)).await?;
             },
             Request::RunKernel => {
                 handle_run_kernel(Some(stream), &control).await?;
@@ -338,9 +340,10 @@ pub fn main(timer: GlobalTimer, cfg: &config::Config) {
     moninj::start(timer);
 
     let control: Rc<RefCell<kernel::Control>> = Rc::new(RefCell::new(kernel::Control::start()));
+    let idle_kernel = Rc::new(cfg.read("idle").ok());
     if let Ok(buffer) = cfg.read("startup") {
         info!("Loading startup kernel...");
-        if let Ok(()) = task::block_on(load_kernel(buffer, &control, None)) {
+        if let Ok(()) = task::block_on(load_kernel(&buffer, &control, None)) {
             info!("Starting startup kernel...");
             let _ = task::block_on(handle_run_kernel(None, &control));
             info!("Startup kernel finished!");
@@ -350,14 +353,53 @@ pub fn main(timer: GlobalTimer, cfg: &config::Config) {
     }
 
     task::spawn(async move {
+        let (tx, rx) = sync_channel!(u32, 1);
+        let tx = RefCell::new(tx);
+        let rx = Rc::new(RefCell::new(rx));
+        let has_connection = Rc::new(RefCell::new(false));
         loop {
             let stream = TcpStream::accept(1381, 2048, 2048).await.unwrap();
+            let has_connection = has_connection.clone();
+
+            if *has_connection.borrow() {
+                let mut tx = tx.borrow_mut();
+                tx.async_send(42).await;
+                // the second send is used to block until another connection received the abort
+                // request.
+                tx.async_send(42).await;
+            }
+
+            *has_connection.borrow_mut() = true;
             let control = control.clone();
-            task::spawn(async {
-                info!("received connection");
-                let _ = handle_connection(&stream, control)
-                    .await
-                    .map_err(|e| warn!("connection terminated: {}", e));
+            let idle_kernel = idle_kernel.clone();
+            let _ = rx.borrow_mut().try_recv();
+
+            let new_rx = rx.clone();
+            task::spawn(async move {
+                let mut new_rx = new_rx.borrow_mut();
+                select_biased! {
+                    _ = (async {
+                        let _ = handle_connection(&stream, control.clone())
+                            .await
+                            .map_err(|e| warn!("connection terminated: {}", e));
+                        if let Some(buffer) = &*idle_kernel {
+                            info!("Loading idle kernel");
+                            let _ = load_kernel(&buffer, &control, None)
+                                .await.map_err(|e| warn!("error loading idle kernel"));
+                            info!("Running idle kernel");
+                            let _ = handle_run_kernel(None, &control)
+                                .await.map_err(|e| warn!("error running idle kernel"));
+                            info!("Idle kernel terminated");
+                        }
+                    }).fuse() => (),
+                    _ = new_rx.async_recv().fuse() => ()
+                }
+                *has_connection.borrow_mut() = false;
+                // it is possible that when `handle_connection` is terminating,
+                // another connection sent an abort request and get blocked,
+                // so we try_recv here to unblock in that case.
+                let _ = new_rx.try_recv();
+                core::mem::drop(new_rx);
                 let _ = stream.flush().await;
                 let _ = stream.abort().await;
             });