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本文主要研究一下nacos RaftCore的MasterElection

RaftCore

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/consistency/persistent/raft/RaftCore.java

@Component
public class RaftCore {
	
	//......

    @PostConstruct
    public void init() throws Exception {

        Loggers.RAFT.info("initializing Raft sub-system"
 
);

        executor.submit(notifier);

        long start = System.currentTimeMillis();

        raftStore.loadDatums(notifier,datums);

        setTerm(NumberUtils.toLong(raftStore.loadMeta().getProperty("term"),0L));

        Loggers.RAFT.info("cache loaded,datum count: {},current term: {}",datums.size(),peers.getTerm());

        while
 
 (true) {
            if (notifier.tasks.size() <= 0) {
                break;
            }
            Thread.sleep(1000L);
        }

        initialized = true;

        Loggers.RAFT.info("finish to load data from disk,cost: {} ms.",(System.currentTimeMillis() - start));

        GlobalExecutor.registerMasterElection(new MasterElection());
        GlobalExecutor.registerHeartbeat(new HeartBeat());

        Loggers.RAFT.info("timer started: leader timeout ms: {},heart-beat timeout ms: {}"
 
,GlobalExecutor.LEADER_TIMEOUT_MS,GlobalExecutor.HEARTBEAT_INTERVAL_MS);
    }

	//......
}
複製程式碼

• RaftCore的init方法通過GlobalExecutor.registerMasterElection(new MasterElection())註冊了MasterElection

GlobalExecutor

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/misc/GlobalExecutor.java

public class GlobalExecutor {

	//......

    public static final long TICK_PERIOD_MS = TimeUnit.MILLISECONDS.toMillis(500L);

    public static void registerMasterElection(Runnable runnable) {
        executorService.scheduleAtFixedRate(runnable,TICK_PERIOD_MS,TimeUnit.MILLISECONDS);
    }

    //......
}
複製程式碼

• registerMasterElection方法每隔TICK_PERIOD_MS毫秒排程一次runnable

MasterElection

nacos-1.1.3/naming/src/main/java/com/alibaba/nacos/naming/consistency/persistent/raft/RaftCore.java

    public class MasterElection implements Runnable {
        @Override
        public void run() {
            try {

                if (!peers.isReady()) {
                    return;
                }

                RaftPeer local = peers.local();
                local.leaderDueMs -= GlobalExecutor.TICK_PERIOD_MS;

                if (local.leaderDueMs > 0) {
                    return;
                }

                // reset timeout
                local.resetLeaderDue();
                local.resetHeartbeatDue();

                sendVote();
            } catch (Exception e) {
                Loggers.RAFT.warn("[RAFT] error while master election {}",e);
            }

        }

        public void sendVote() {

            RaftPeer local = peers.get(NetUtils.localServer());
            Loggers.RAFT.info("leader timeout,start voting,leader: {},term: {}",JSON.toJSONString(getLeader()),local.term);

            peers.reset();

            local.term.incrementAndGet();
            local.voteFor = local.ip;
            local.state = RaftPeer.State.CANDIDATE;

            Map<String,String> params = new HashMap<>(1);
            params.put("vote",JSON.toJSONString(local));
            for (final String server : peers.allServersWithoutMySelf()) {
                final String url = buildURL(server,API_VOTE);
                try {
                    HttpClient.asyncHttpPost(url,null,params,new AsyncCompletionHandler<Integer>() {
                        @Override
                        public Integer onCompleted(Response response) throws Exception {
                            if (response.getStatusCode() != HttpURLConnection.HTTP_OK) {
                                Loggers.RAFT.error("NACOS-RAFT vote failed: {},url: {}",response.getResponseBody(),url);
                                return 1;
                            }

                            RaftPeer peer = JSON.parseObject(response.getResponseBody(),RaftPeer.class);

                            Loggers.RAFT.info("received approve from peer: {}",JSON.toJSONString(peer));

                            peers.decideLeader(peer);

                            return 0;
                        }
                    });
                } catch (Exception e) {
                    Loggers.RAFT.warn("error while sending vote to server: {}",server);
                }
            }
        }
    }
複製程式碼

• MasterElection實現了Runnable方法，其run方法在peers都是ready而且local.leaderDueMs減去TICK_PERIOD_MS小於等於0的時候會開始選舉；它首先resetLeaderDue及resetHeartbeatDue，然後執行sendVote方法；sendVote方法首先重置peers，遞增localPeer的term，並設定voteFor為自己，然後更新state為RaftPeer.State.CANDIDATE，最後遍歷peers.allServersWithoutMySelf()，將自己的vote資訊非同步post給其他peer；如果其他peer返回成功則執行peers.decideLeader(peer)，返回1，否則返回0

小結

RaftCore的init方法通過GlobalExecutor.registerMasterElection(new MasterElection())註冊了MasterElection；registerMasterElection方法每隔TICK_PERIOD_MS毫秒排程一次；MasterElection實現了Runnable方法，其run方法在peers都是ready而且local.leaderDueMs減去TICK_PERIOD_MS小於等於0的時候會開始選舉；它首先resetLeaderDue及resetHeartbeatDue，然後執行sendVote方法

doc

• RaftCore