state: drop epoch_tx

The stamp is the only lock-free epoch label.

2 files changed, 7 insertions, 8 deletions

diff --git a/src/state/host.rs b/src/state/host.rs
index 6bb9d3b..7c3e165 100644
--- a/src/state/host.rs
+++ b/src/state/host.rs
@@ -283,10 +283,10 @@ impl Host for AppState {
                     replica.epoch = epoch;
                     replica.epoch_seq += 1;
                     replica.writable = writable;
+                    // Publishes the epoch with the heads (`Replica::stamps`), under the
+                    // same lock, so it never disagrees with the document for anyone
+                    // holding the lock.
                     replica.refresh_heads();
-                    // Updated under the same lock, so the cached epoch never disagrees
-                    // with the document for anyone holding the lock.
-                    state.epoch_tx.send_replace(epoch);
                     // Reset every peer's sync state before the lock is released, so no
                     // message is generated from or applied to a state that describes the
                     // old document. (Lock order doc -> peer, as in sync generation.)
diff --git a/src/state/mod.rs b/src/state/mod.rs
index 9ee08b7..5e4a4d3 100644
--- a/src/state/mod.rs
+++ b/src/state/mod.rs
@@ -59,10 +59,9 @@ pub(crate) struct AppState {
     /// The document and its epoch. Derefs to `Document`.
     pub(crate) doc: Arc<DocumentLock>,
 
-    /// Copy of `doc.epoch` for cheap, lock-free reads (handshakes, keepalives, /peers).
-    /// Only ever changed while holding `doc`'s write lock, together with `doc.epoch`.
-    pub(crate) epoch_tx: watch::Sender<Epoch>,
-    /// `doc`'s epoch label and heads, readable without its lock (`Replica::stamps`).
+    /// `doc`'s epoch label and heads, readable without its lock (`Replica::stamps`):
+    /// for cheap reads (handshakes, keepalives, /peers). Only ever changed while holding
+    /// `doc`'s write lock, together with `doc.epoch`.
     pub(crate) stamp: watch::Receiver<Stamp>,
 
     pub(crate) lifecycle: Arc<RwLock<NodeLifecycle>>,
@@ -231,7 +230,7 @@ impl AppState {
     /// The local epoch. Code that labels or applies sync messages must use the epoch
     /// of the locked `Replica` instead, so label and document can't disagree.
     pub(crate) fn local_epoch(&self) -> Epoch {
-        *self.epoch_tx.borrow()
+        self.stamp.borrow().epoch
     }
 
     /// The local epoch and `Replica::epoch_seq`, read together, without waiting for the