safe main-thread panics; save cannot happen until server initialised

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "markov"
-version = "0.7.1"
+version = "0.7.2"
 description = "Generate string of text from Markov chain fed by stdin"
 authors = ["Avril <flanchan@cumallover.me>"]
 edition = "2018"

src/ext.rs

@@ -137,6 +137,18 @@ impl<T> AssertNotSend<T>
     t
 }
 
+/// Require a value implements a specific trait
+#[macro_export] macro_rules! require_impl {
+    ($t:path: $val:expr) => {
+	{
+	    #[inline(always)] fn require_impl<T: $t >(val: T) -> T {
+		val
+	    }
+	    require_impl($val)
+	}
+    }
+}
+
 impl<T> Deref for AssertNotSend<T>
 {
     type Target = T;

src/main.rs

@@ -71,6 +71,7 @@ mod api;
 #[cfg(target_family="unix")]
 mod signals;
 mod config;
+mod msg;
 mod state;
 use state::State;
 mod save;
@@ -139,7 +140,7 @@ async fn main() {
 				   Arc::clone(&chain),
 				   Arc::clone(&save_when));
 	    let state2 = state.clone();
-	    let saver = tokio::spawn(save::host(state.clone()));
+	    let saver = tokio::spawn(save::host(Box::new(state.clone())));
 	    let chain = warp::any().map(move || state.clone());
 
 	    tasks.push(saver.map(|res| res.expect("Saver panicked")).boxed());
@@ -256,8 +257,8 @@ async fn main() {
 	#[cfg(target_family="unix")]
 	tasks.push(tokio::spawn(signals::handle(state.clone())).map(|res| res.expect("Signal handler panicked")).boxed());
 
-	require_send(async {
-	    let server = {
+	require_impl!(Send: async {
+	    let (server, init) = {
 		let s2 = AssertNotSend::new(state.clone()); //temp clone the Arcs here for shutdown if server fails to bind, assert they cannot remain cloned across an await boundary.
 		match bind::try_serve(warp::serve(push
 						  .or(read)),
@@ -268,7 +269,7 @@ async fn main() {
 				      }) {
 		    Ok((addr, server)) => {
 			info!("Server bound on {:?}", addr);
-			server
+			(server, s2.into_inner().into_save_initialiser())
 		    },
 		    Err(err) => {
 			error!("Failed to bind server: {}", err);
@@ -277,7 +278,13 @@ async fn main() {
 		    },
 		}
 	    };
-	    server.await;
+	    tokio::join![
+		server,
+		async move {
+		    trace!("Init set");
+		    init.set().expect("Failed to initialise saver")
+		},
+	    ];
 	}).await;
 	
 	// Cleanup

src/msg.rs

@@ -0,0 +1,108 @@
+//! Message passing things
+use super::*;
+use tokio::{
+    sync::{
+	watch,
+    },
+};
+use std::{
+    task::{Poll, Context},
+    pin::Pin,
+    fmt,
+    error,
+};
+use futures::{
+    future::Future,
+};
+
+#[derive(Debug)]
+pub struct InitError;
+#[derive(Debug)]
+pub struct InitWaitError;
+
+impl error::Error for InitError{}
+impl fmt::Display for InitError
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "failed to set init value")
+    }
+}
+
+impl error::Error for InitWaitError{}
+impl fmt::Display for InitWaitError
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "failed to receive init value")
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct Initialiser
+{
+    tx: Arc<watch::Sender<bool>>,
+    rx: watch::Receiver<bool>
+}
+
+impl Initialiser
+{
+    pub fn new() -> Self
+    {
+	let (tx, rx) = watch::channel(false);
+	Self {
+	    tx: Arc::new(tx),
+	    rx,
+	}
+    }
+
+    pub fn new_set() -> Self
+    {
+	let (tx, rx) = watch::channel(true);
+	Self {
+	    tx: Arc::new(tx),
+	    rx,
+	}
+    }
+
+    pub async fn wait(&mut self) -> Result<(), InitWaitError>
+    {
+	if !*self.rx.borrow() {
+	    self.rx.recv().await
+		.ok_or_else(|| InitWaitError)
+		.and_then(|x| if x {Ok(())} else {Err(InitWaitError)})
+	} else {
+	    Ok(())
+	}
+    }
+
+    pub fn is_set(&self) -> bool
+    {
+	*self.rx.borrow()
+    }
+    
+    pub fn set(self) -> Result<(), InitError>
+    {
+	if !*self.rx.borrow() {
+	    self.tx.broadcast(true).map_err(|_| InitError)
+	} else {
+	    Ok(())
+	}
+    }
+}
+
+impl Future for Initialiser
+{
+    type Output = Result<(), InitWaitError>;
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+	
+	if !*self.rx.borrow() {
+	    let rx = self.rx.recv();
+	    tokio::pin!(rx);
+	    rx.poll(cx).map(|x| x.ok_or_else(|| InitWaitError)
+			    .and_then(|x| if x {Ok(())} else {Err(InitWaitError)}))
+	} else {
+	    Poll::Ready(Ok(()))
+	}
+    }
+}

src/save.rs

@@ -73,10 +73,12 @@ async fn save_now_to(chain: &Chain<String>, to: impl AsRef<Path>) -> io::Result<
 }
 
 /// Start the save loop for this chain
-pub async fn host(mut state: State)
+pub async fn host(mut state: Box<State>)
 {
     let to = state.config().file.to_owned();
     let interval = state.config().save_interval();
+    if state.on_init_save().await.is_ok() {
+	trace!("Init get");
 	while Arc::strong_count(state.when()) > 1 {
 	    {
 		let chain = state.chain().read().await;
@@ -99,6 +101,9 @@ pub async fn host(mut state: State)
 		break;
 	    }
 	}
+    } else {
+	trace!("Shutdown called before init completed");
+    }
     trace!("Saver exiting");
 }
 

src/state.rs

@@ -6,6 +6,20 @@ use tokio::{
     },
 };
 use config::Config;
+use msg::Initialiser;
+
+#[derive(Debug)]
+pub struct ShutdownError;
+
+impl error::Error for ShutdownError{}
+impl fmt::Display for ShutdownError
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result
+    {
+	write!(f, "shutdown signal caught")
+    }
+}
+
 
 #[derive(Debug, Clone)]
 pub struct State
@@ -14,6 +28,7 @@ pub struct State
     exclude: Arc<(sanitise::filter::Filter, sanitise::filter::Filter)>,
     chain: Arc<RwLock<Chain<String>>>,
     save: Arc<Notify>,
+    save_begin: Initialiser,
 
     shutdown: Arc<watch::Sender<bool>>,
     shutdown_recv: watch::Receiver<bool>,
@@ -21,6 +36,39 @@ pub struct State
 
 impl State
 {
+    /// Consume this `state` into its initialiser
+    pub fn into_save_initialiser(self) -> Initialiser
+    {
+	self.save_begin
+    }
+
+    /// Allow the saver task to start work
+    pub fn init_save(self) -> Result<(), msg::InitError>
+    {
+	self.save_begin.set()
+    }
+
+    /// Has `init_save` been called?
+    pub fn is_init_save(&self) -> bool
+    {
+	self.save_begin.is_set()
+    }
+
+    /// A future that completes either when `init_save` is called, or `shutdown`.
+    pub async fn on_init_save(&mut self) -> Result<(), ShutdownError>
+    {
+	tokio::select!{
+	    Ok(()) = self.save_begin.wait() => {
+		Ok(())
+	    }
+	    Some(true) = self.shutdown_recv.recv() => {
+		debug!("on_init_save(): shutdown received");
+		Err(ShutdownError)
+	    }
+	    else => Err(ShutdownError)
+	}
+    }
+    
     pub fn inbound_filter(&self) -> &sanitise::filter::Filter
     {
 	&self.exclude.0
@@ -39,6 +87,7 @@ impl State
 	    config: Arc::new(config),
 	    chain,
 	    save,
+	    save_begin: Initialiser::new(),
 	    shutdown: Arc::new(shutdown),
 	    shutdown_recv,
 	}