document: allow writes during rejoin

1 files changed, 21 insertions, 6 deletions

diff --git a/src/state/read.rs b/src/state/read.rs
index a9b3116..e325e61 100644
--- a/src/state/read.rs
+++ b/src/state/read.rs
@@ -1,4 +1,5 @@
-//! Serving reads: from the live document, or from the pre-rejoin copy while rejoining.
+//! Serving reads: from the live document, or from the pre-rejoin document while
+//! rejoining.
 
 use std::sync::Arc;
 
@@ -7,10 +8,13 @@ use crate::document::replica::Epoch;
 use crate::document::{ChangeHash, Document};
 use crate::locks::RwLockExt;
 
-/// A read-only view of the document the node served before it started rejoining.
+/// The document the node served before it started rejoining, of the epoch it left:
+/// reads are answered from it (marked stale), and writes go into it
+/// (`AppState::mutate_doc`), until the rejoin replays them into the new epoch or
+/// restores this document (`Host::finish_rejoin`, `Host::abandon_rejoin`).
 pub(crate) struct StaleView {
     pub(crate) epoch: Epoch,
-    pub(crate) doc: Arc<Document>,
+    pub(crate) doc: Arc<std::sync::RwLock<Document>>,
 }
 
 /// Where a read was served from.
@@ -57,9 +61,12 @@ impl AppState {
             return Err(axum::http::StatusCode::SERVICE_UNAVAILABLE);
         };
 
-        let rendered = tokio::task::spawn_blocking(move || finish(read(&doc)))
-            .await
-            .expect("document read task panicked");
+        let rendered = tokio::task::spawn_blocking(move || {
+            let data = read(&doc.read_or_recover());
+            finish(data)
+        })
+        .await
+        .expect("document read task panicked");
         Ok((rendered, ReadSource::Stale(epoch), None))
     }
 
@@ -93,4 +100,12 @@ impl AppState {
     pub(super) fn set_stale(&self, view: Option<StaleView>) {
         *self.stale.write_or_recover() = view;
     }
+
+    /// The stale view's document and epoch, if there is one.
+    pub(crate) fn stale_document(&self) -> Option<(Epoch, Arc<std::sync::RwLock<Document>>)> {
+        self.stale
+            .read_or_recover()
+            .as_ref()
+            .map(|view| (view.epoch, Arc::clone(&view.doc)))
+    }
 }