Refactor: move leadership condition forward.

src/sync_log_entries.rs

@@ -201,42 +201,44 @@ where
             Ok(SyncLogEntriesResult::Success) => {
                 let mut rf = rf.lock();
 
-                if rf.current_term != term {
-                    return;
-                }
-
                 check_or_record!(
                     match_index < rf.log.end(),
                     ErrorKind::LeaderLogShrunk(match_index),
                     "The leader log shrunk",
                     &rf
                 );
+
+                if !rf.is_leader() {
+                    return;
+                }
+
+                if rf.current_term != term {
+                    return;
+                }
+
                 rf.next_index[peer_index] = match_index + 1;
                 rf.current_step[peer_index] = 0;
                 if match_index > rf.match_index[peer_index] {
                     rf.match_index[peer_index] = match_index;
-                    if rf.is_leader() && rf.current_term == term {
-                        let mut matched = rf.match_index.to_vec();
-                        let mid = matched.len() / 2 + 1;
-                        matched.sort_unstable();
-                        let new_commit_index = matched[mid];
-                        if new_commit_index > rf.commit_index
-                            && rf.log.at(new_commit_index).term
-                                == rf.current_term
-                        {
-                            log::info!(
-                                "{:?} moving leader commit index to {} in {:?}",
-                                rf.leader_id,
-                                new_commit_index,
-                                task_number
-                            );
-                            // COMMIT_INDEX_INVARIANT, SNAPSHOT_INDEX_INVARIANT:
-                            // Index new_commit_index exists in the log array,
-                            // which implies new_commit_index is in range
-                            // [log.start(), log.end()).
-                            rf.commit_index = new_commit_index;
-                            apply_command_signal.notify_one();
-                        }
+                    let mut matched = rf.match_index.to_vec();
+                    let mid = matched.len() / 2 + 1;
+                    matched.sort_unstable();
+                    let new_commit_index = matched[mid];
+                    if new_commit_index > rf.commit_index
+                        && rf.log.at(new_commit_index).term == rf.current_term
+                    {
+                        log::info!(
+                            "{:?} moving leader commit index to {} in {:?}",
+                            rf.leader_id,
+                            new_commit_index,
+                            task_number
+                        );
+                        // COMMIT_INDEX_INVARIANT, SNAPSHOT_INDEX_INVARIANT:
+                        // Index new_commit_index exists in the log array,
+                        // which implies new_commit_index is in range
+                        // [log.start(), log.end()).
+                        rf.commit_index = new_commit_index;
+                        apply_command_signal.notify_one();
                     }
                 }
                 // After each round of install snapshot, we must schedule
@@ -263,10 +265,7 @@ where
                 // by the previous append entries request. Thus the match index
                 // did not move. Still, we need the extra round of append
                 // entries to peer X for log entry at index 12.
-                if rf.is_leader()
-                    && rf.current_term == term
-                    && prev_log_index == match_index
-                {
+                if prev_log_index == match_index {
                     // If we did not make any progress this time, try again.
                     // This can only happen when installing snapshots.
                     let _ = rerun.send(Some(Peer(peer_index)));