From 45772bb7ec79bced76e546375c3acecce0ca4563 Mon Sep 17 00:00:00 2001
From: Xiangpeng Hu <65238551+BUAAserein@users.noreply.github.com>
Date: Fri, 28 Jul 2023 22:42:10 +0800
Subject: [PATCH] RATIS-1861. NullPointerException in readAsync when Ratis
 leader is changing (#895)

---
 .../java/org/apache/ratis/server/impl/RaftServerImpl.java    | 3 ++-
 .../src/main/java/org/apache/ratis/server/impl/RoleInfo.java | 5 ++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java b/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java
index a857faa870..add6b041da 100644
--- a/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java
+++ b/ratis-server/src/main/java/org/apache/ratis/server/impl/RaftServerImpl.java
@@ -603,10 +603,11 @@ synchronized void changeToLeader() {
     Preconditions.assertTrue(getInfo().isCandidate());
     role.shutdownLeaderElection();
     setRole(RaftPeerRole.LEADER, "changeToLeader");
+    final LeaderStateImpl leader = role.updateLeaderState(this);
     state.becomeLeader();
 
     // start sending AppendEntries RPC to followers
-    final LogEntryProto e = role.startLeaderState(this);
+    final LogEntryProto e = leader.start();
     getState().setRaftConf(e);
   }
 
diff --git a/ratis-server/src/main/java/org/apache/ratis/server/impl/RoleInfo.java b/ratis-server/src/main/java/org/apache/ratis/server/impl/RoleInfo.java
index d09c8017bc..603ba13260 100644
--- a/ratis-server/src/main/java/org/apache/ratis/server/impl/RoleInfo.java
+++ b/ratis-server/src/main/java/org/apache/ratis/server/impl/RoleInfo.java
@@ -18,7 +18,6 @@
 
 package org.apache.ratis.server.impl;
 
-import org.apache.ratis.proto.RaftProtos.LogEntryProto;
 import org.apache.ratis.proto.RaftProtos.RaftPeerRole;
 import org.apache.ratis.protocol.RaftPeerId;
 import org.apache.ratis.util.Preconditions;
@@ -79,8 +78,8 @@ LeaderStateImpl getLeaderStateNonNull() {
     return Objects.requireNonNull(leaderState.get(), "leaderState is null");
   }
 
-  LogEntryProto startLeaderState(RaftServerImpl server) {
-    return updateAndGet(leaderState, new LeaderStateImpl(server)).start();
+  LeaderStateImpl updateLeaderState(RaftServerImpl server) {
+    return updateAndGet(leaderState, new LeaderStateImpl(server));
   }
 
   void shutdownLeaderState(boolean allowNull) {