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hdfs/dataNode启动过程.md
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hdfs/dataNode启动过程.md
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# 启动
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## createDataNode
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DataNode核心启动类是从createDataNode开始的。
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```java
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public static DataNode createDataNode(String args[], Configuration conf,
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SecureResources resources) throws IOException {
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// 初始化DataNode,核心函数在makeInstance里面的new DataNode()进行初始化。
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DataNode dn = instantiateDataNode(args, conf, resources);
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if (dn != null) {
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// 启动DataNode
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dn.runDatanodeDaemon();
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}
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return dn;
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}
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```
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### makeInstance
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```java
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static DataNode makeInstance(Collection<StorageLocation> dataDirs,
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Configuration conf, SecureResources resources) throws IOException {
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List<StorageLocation> locations;
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StorageLocationChecker storageLocationChecker =
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new StorageLocationChecker(conf, new Timer());
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try {
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// 对存储路径进行检查。返回可用的位置。
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locations = storageLocationChecker.check(conf, dataDirs);
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} catch (InterruptedException ie) {
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throw new IOException("Failed to instantiate DataNode", ie);
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}
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DefaultMetricsSystem.initialize("DataNode");
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assert locations.size() > 0 : "number of data directories should be > 0";
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// 初始化DataNode实例。在构造函数里面startDataNode比较重要，是启动DataNode的核心函数，需要重点关注。
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return new DataNode(conf, locations, storageLocationChecker, resources);
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}
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```
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### startDataNode
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```java
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void startDataNode(List<StorageLocation> dataDirectories,
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SecureResources resources
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) throws IOException {
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// settings global for all BPs in the Data Node
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this.secureResources = resources;
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synchronized (this) {
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this.dataDirs = dataDirectories;
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}
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this.dnConf = new DNConf(this);
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checkSecureConfig(dnConf, getConf(), resources);
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// ... 省略 ....
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storage = new DataStorage();
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// global DN settings
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registerMXBean();
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// 初始化dataXceiver服务：用于DN接受客户端和其他DN发送过来的数据的服务。
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initDataXceiver();
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// 初始化HTTP服务。
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startInfoServer();
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//TODO 待定。
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pauseMonitor = new JvmPauseMonitor();
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pauseMonitor.init(getConf());
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pauseMonitor.start();
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// BlockPoolTokenSecretManager is required to create ipc server.
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this.blockPoolTokenSecretManager = new BlockPoolTokenSecretManager();
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// Login is done by now. Set the DN user name.
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dnUserName = UserGroupInformation.getCurrentUser().getUserName();
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LOG.info("dnUserName = {}", dnUserName);
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LOG.info("supergroup = {}", supergroup);
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// 初始化DN的RPC调用服务。
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initIpcServer();
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metrics = DataNodeMetrics.create(getConf(), getDisplayName());
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peerMetrics = dnConf.peerStatsEnabled ?
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DataNodePeerMetrics.create(getDisplayName(), getConf()) : null;
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metrics.getJvmMetrics().setPauseMonitor(pauseMonitor);
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ecWorker = new ErasureCodingWorker(getConf(), this);
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blockRecoveryWorker = new BlockRecoveryWorker(this);
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blockPoolManager = new BlockPoolManager(this);
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// DN向NN注册，其中核心的函数为doRefreshNamenodes
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blockPoolManager.refreshNamenodes(getConf());
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// Create the ReadaheadPool from the DataNode context so we can
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// exit without having to explicitly shutdown its thread pool.
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readaheadPool = ReadaheadPool.getInstance();
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saslClient = new SaslDataTransferClient(dnConf.getConf(),
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dnConf.saslPropsResolver, dnConf.trustedChannelResolver);
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saslServer = new SaslDataTransferServer(dnConf, blockPoolTokenSecretManager);
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startMetricsLogger();
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if (dnConf.diskStatsEnabled) {
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diskMetrics = new DataNodeDiskMetrics(this,
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dnConf.outliersReportIntervalMs, getConf());
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}
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}
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```
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### doRefreshNamenodes
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主要是向NN注册当前DN。
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```java
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private void doRefreshNamenodes(
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Map<String, Map<String, InetSocketAddress>> addrMap,
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Map<String, Map<String, InetSocketAddress>> lifelineAddrMap)
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throws IOException {
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Set<String> toRefresh = Sets.newLinkedHashSet();
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Set<String> toAdd = Sets.newLinkedHashSet();
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Set<String> toRemove;
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synchronized (this) {
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// Step 1. For each of the new nameservices, figure out whether
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// it's an update of the set of NNs for an existing NS,
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// or an entirely new nameservice.
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// 判断当前DN中的nameservice是否已经存在：如果已经存在则需要刷新；否则需要添加。
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for (String nameserviceId : addrMap.keySet()) {
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if (bpByNameserviceId.containsKey(nameserviceId)) {
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toRefresh.add(nameserviceId);
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} else {
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toAdd.add(nameserviceId);
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}
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}
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// Step 2. Any nameservices we currently have but are no longer present
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// need to be removed.
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// 计算当前DN需要删除的nameservice
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toRemove = Sets.newHashSet(Sets.difference(
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bpByNameserviceId.keySet(), addrMap.keySet()));
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// Step 3. 启动新的nameservice
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if (!toAdd.isEmpty()) {
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for (String nsToAdd : toAdd) {
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Map<String, InetSocketAddress> nnIdToAddr = addrMap.get(nsToAdd);
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Map<String, InetSocketAddress> nnIdToLifelineAddr =
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lifelineAddrMap.get(nsToAdd);
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ArrayList<InetSocketAddress> addrs =
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Lists.newArrayListWithCapacity(nnIdToAddr.size());
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ArrayList<String> nnIds =
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Lists.newArrayListWithCapacity(nnIdToAddr.size());
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ArrayList<InetSocketAddress> lifelineAddrs =
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Lists.newArrayListWithCapacity(nnIdToAddr.size());
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for (String nnId : nnIdToAddr.keySet()) {
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addrs.add(nnIdToAddr.get(nnId));
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nnIds.add(nnId);
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lifelineAddrs.add(nnIdToLifelineAddr != null ?
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nnIdToLifelineAddr.get(nnId) : null);
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}
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BPOfferService bpos = createBPOS(nsToAdd, nnIds, addrs,
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lifelineAddrs);
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bpByNameserviceId.put(nsToAdd, bpos);
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offerServices.add(bpos);
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}
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}
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startAll();
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}
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// Step 4. 停止掉老的nameservice. This happens outside
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// of the synchronized(this) lock since they need to call
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// back to .remove() from another thread
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if (!toRemove.isEmpty()) {
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for (String nsToRemove : toRemove) {
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BPOfferService bpos = bpByNameserviceId.get(nsToRemove);
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bpos.stop();
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bpos.join();
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// they will call remove on their own
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}
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}
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// Step 5. Update nameservices whose NN list has changed
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// 更新nameservices
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if (!toRefresh.isEmpty()) {
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for (String nsToRefresh : toRefresh) {
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BPOfferService bpos = bpByNameserviceId.get(nsToRefresh);
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Map<String, InetSocketAddress> nnIdToAddr = addrMap.get(nsToRefresh);
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Map<String, InetSocketAddress> nnIdToLifelineAddr =
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lifelineAddrMap.get(nsToRefresh);
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ArrayList<InetSocketAddress> addrs =
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Lists.newArrayListWithCapacity(nnIdToAddr.size());
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ArrayList<InetSocketAddress> lifelineAddrs =
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Lists.newArrayListWithCapacity(nnIdToAddr.size());
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ArrayList<String> nnIds = Lists.newArrayListWithCapacity(
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nnIdToAddr.size());
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for (String nnId : nnIdToAddr.keySet()) {
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addrs.add(nnIdToAddr.get(nnId));
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lifelineAddrs.add(nnIdToLifelineAddr != null ?
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nnIdToLifelineAddr.get(nnId) : null);
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nnIds.add(nnId);
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}
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try {
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UserGroupInformation.getLoginUser()
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.doAs(new PrivilegedExceptionAction<Object>() {
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@Override
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public Object run() throws Exception {
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// 刷新NNList 核心实现.
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bpos.refreshNNList(nsToRefresh, nnIds, addrs, lifelineAddrs);
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return null;
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}
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});
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} catch (InterruptedException ex) {
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IOException ioe = new IOException();
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ioe.initCause(ex.getCause());
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throw ioe;
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}
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}
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}
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}
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```
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