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fix(client): disconnect_reason/read_error is cancel-safe #1347

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merged 3 commits into from
Apr 8, 2024
Merged

fix(client): disconnect_reason/read_error is cancel-safe #1347

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84a0f59
client: `disconnect_reason/read_error` cancel-safe
niklasad1 Apr 8, 2024
055a31a
fix wasm build
niklasad1 Apr 8, 2024
b7e0237
remove async_lock dependency
niklasad1 Apr 8, 2024
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82 changes: 27 additions & 55 deletions core/src/client/async_client/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -145,64 +145,36 @@ impl ThreadSafeRequestManager {
self.0.lock().expect("Not poisoned; qed")
}
}

pub(crate) type SharedDisconnectReason = Arc<AsyncRwLock<Option<Arc<Error>>>>;
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/// If the background thread is terminated, this type
/// can be used to read the error cause.
///
// NOTE: This is an AsyncRwLock to be &self.
#[derive(Debug)]
struct ErrorFromBack(AsyncRwLock<Option<ReadErrorOnce>>);
struct ErrorFromBack {
conn: mpsc::Sender<FrontToBack>,
disconnect_reason: SharedDisconnectReason,
}

impl ErrorFromBack {
fn new(unread: oneshot::Receiver<Error>) -> Self {
Self(AsyncRwLock::new(Some(ReadErrorOnce::Unread(unread))))
fn new(conn: mpsc::Sender<FrontToBack>, disconnect_reason: SharedDisconnectReason) -> Self {
Self { conn, disconnect_reason }
}

async fn read_error(&self) -> Error {
const PROOF: &str = "Option is only is used to workaround ownership issue and is always Some; qed";
// When the background task is closed the error is written to `disconnect_reason`.
self.conn.closed().await;

if let ReadErrorOnce::Read(ref err) = self.0.read().await.as_ref().expect(PROOF) {
return Error::RestartNeeded(err.clone());
};

let mut write = self.0.write().await;
let state = write.take();

let err = match state.expect(PROOF) {
ReadErrorOnce::Unread(rx) => {
let arc_err = Arc::new(match rx.await {
Ok(err) => err,
// This should never happen because the receiving end is still alive.
// Before shutting down the background task a error message should
// be emitted.
Err(_) => Error::Custom(
"Error reason could not be found. This is a bug. Please open an issue.".to_string(),
),
});
*write = Some(ReadErrorOnce::Read(arc_err.clone()));
arc_err
}
ReadErrorOnce::Read(arc_err) => {
*write = Some(ReadErrorOnce::Read(arc_err.clone()));
arc_err
}
};

Error::RestartNeeded(err)
if let Some(err) = self.disconnect_reason.read().await.as_ref() {
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Now we're not holding this lock over any await points (at least, I think we aren't?), should we make it a sync RwLock?

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done nice catch, one dependency removed :)

Error::RestartNeeded(err.clone())
} else {
Error::Custom("Error reason could not be found. This is a bug. Please open an issue.".to_string())
}
}
}

/// Wrapper over a [`oneshot::Receiver`] that reads
/// the underlying channel once and then stores the result in String.
/// It is possible that the error is read more than once if several calls are made
/// when the background thread has been terminated.
#[derive(Debug)]
enum ReadErrorOnce {
/// Error message is already read.
Read(Arc<Error>),
/// Error message is unread.
Unread(oneshot::Receiver<Error>),
}

/// Builder for [`Client`].
#[derive(Debug, Copy, Clone)]
pub struct ClientBuilder {
Expand Down Expand Up @@ -318,7 +290,7 @@ impl ClientBuilder {
R: TransportReceiverT + Send,
{
let (to_back, from_front) = mpsc::channel(self.max_concurrent_requests);
let (err_to_front, err_from_back) = oneshot::channel::<Error>();
let disconnect_reason = SharedDisconnectReason::default();
let max_buffer_capacity_per_subscription = self.max_buffer_capacity_per_subscription;
let (client_dropped_tx, client_dropped_rx) = oneshot::channel();
let (send_receive_task_sync_tx, send_receive_task_sync_rx) = mpsc::channel(1);
Expand Down Expand Up @@ -366,12 +338,12 @@ impl ClientBuilder {
inactivity_stream,
}));

tokio::spawn(wait_for_shutdown(send_receive_task_sync_rx, client_dropped_rx, err_to_front));
tokio::spawn(wait_for_shutdown(send_receive_task_sync_rx, client_dropped_rx, disconnect_reason.clone()));

Client {
to_back,
to_back: to_back.clone(),
request_timeout: self.request_timeout,
error: ErrorFromBack::new(err_from_back),
error: ErrorFromBack::new(to_back, disconnect_reason),
id_manager: RequestIdManager::new(self.max_concurrent_requests, self.id_kind),
max_log_length: self.max_log_length,
on_exit: Some(client_dropped_tx),
Expand All @@ -391,7 +363,7 @@ impl ClientBuilder {
type PendingIntervalStream = IntervalStream<Pending<()>>;

let (to_back, from_front) = mpsc::channel(self.max_concurrent_requests);
let (err_to_front, err_from_back) = oneshot::channel::<Error>();
let disconnect_reason = SharedDisconnectReason::default();
let max_buffer_capacity_per_subscription = self.max_buffer_capacity_per_subscription;
let (client_dropped_tx, client_dropped_rx) = oneshot::channel();
let (send_receive_task_sync_tx, send_receive_task_sync_rx) = mpsc::channel(1);
Expand Down Expand Up @@ -423,13 +395,13 @@ impl ClientBuilder {
wasm_bindgen_futures::spawn_local(wait_for_shutdown(
send_receive_task_sync_rx,
client_dropped_rx,
err_to_front,
disconnect_reason.clone(),
));

Client {
to_back,
to_back: to_back.clone(),
request_timeout: self.request_timeout,
error: ErrorFromBack::new(err_from_back),
error: ErrorFromBack::new(to_back, disconnect_reason),
id_manager: RequestIdManager::new(self.max_concurrent_requests, self.id_kind),
max_log_length: self.max_log_length,
on_exit: Some(client_dropped_tx),
Expand Down Expand Up @@ -474,7 +446,7 @@ impl Client {
///
/// # Cancel-safety
///
/// This method is not cancel-safe
/// This method is cancel-safe
pub async fn disconnect_reason(&self) -> Error {
self.error.read_error().await
}
Expand Down Expand Up @@ -1070,14 +1042,14 @@ where
async fn wait_for_shutdown(
mut close_rx: mpsc::Receiver<Result<(), Error>>,
client_dropped: oneshot::Receiver<()>,
err_to_front: oneshot::Sender<Error>,
err_to_front: SharedDisconnectReason,
) {
let rx_item = close_rx.recv();

tokio::pin!(rx_item);

// Send an error to the frontend if the send or receive task completed with an error.
if let Either::Left((Some(Err(err)), _)) = future::select(rx_item, client_dropped).await {
let _ = err_to_front.send(err);
*err_to_front.write().await = Some(Arc::new(err));
}
}