一. 源码仓库:
zookeeper
基于分支 3.4.14 分支在 windows 系统启动流程进行剖析。
二. 流程剖析:
- 源码入口
通过 zkServer.cmd 可执行文件内容能够看出 zookeeper 的服务端是通过 org.apache.zookeeper.server.quorum.QuorumPeerMain 这个类的 main 作为入口来启动服务端程序的.main 办法传入的是咱们 zoo.cfg 文件的地址, 而后通过解析 zoo.cfg 文件, 将 key,value 的配置信息转换成 QuorumPeerConfig 的对象, 转换细节能够看 QuorumPeerConfig.parse 办法, 其中转换后的外围配置参数有:
| 参数名 | 参数形容 |
|---|---|
| dataLogDir | 事务日志存储门路 |
| dataDir | 快照存储门路 |
| electionType | 选举算法, 目前只反对 3 - 疾速选举算法 |
| myid | 以后服务 id |
| tickTime | 工夫单位 |
| initLimit | |
| syncLimit | 事务存储门路 |
| minSessionTimeout | 最小会话超时工夫 |
| maxSessionTimeout | 最大会话超时工夫 |
| peerType | 角色类型 -OBSERVER,PARTICIPANT |
| clientPort | 客户端连贯端口 |
| clientPortAddress | 客户端连贯 Host |
| snapRetainCount | 快照保留个数, 最小为 3 |
| purgeInterval | 快照革除距离 |
| server.sid | hostName:port(通信端口):electionPort(选举端口):peerType |
| maxClientCnxns | 最大客户端连接数 |
拿到解析后的参数后, 能够通过是否配置了 server.id 参数来决定是否集群启动还是单机启动, 单机启动运行通过 ZooKeeperServerMain#main 办法启动, 集群启动则还是在 QuorumPeerMain#runFromConfig 办法进行解决的, 这里咱们就间接解说集群模式, 因为集群模式比单机模式多了集群间的通信相干的解决, 如 Leader 选举, 数据同步, 申请转发等.
public void runFromConfig(QuorumPeerConfig config) throws IOException {
try {ManagedUtil.registerLog4jMBeans();
} catch (JMException e) {LOG.warn("Unable to register log4j JMX control", e);
}
LOG.info("Starting quorum peer");
try {ServerCnxnFactory cnxnFactory = ServerCnxnFactory.createFactory();
cnxnFactory.configure(config.getClientPortAddress(),
config.getMaxClientCnxns());
quorumPeer = getQuorumPeer();
quorumPeer.setQuorumPeers(config.getServers());
quorumPeer.setTxnFactory(new FileTxnSnapLog(new File(config.getDataLogDir()),
new File(config.getDataDir())));
quorumPeer.setElectionType(config.getElectionAlg());
quorumPeer.setMyid(config.getServerId());
quorumPeer.setTickTime(config.getTickTime());
quorumPeer.setInitLimit(config.getInitLimit());
quorumPeer.setSyncLimit(config.getSyncLimit());
quorumPeer.setQuorumListenOnAllIPs(config.getQuorumListenOnAllIPs());
quorumPeer.setCnxnFactory(cnxnFactory);
quorumPeer.setQuorumVerifier(config.getQuorumVerifier());
quorumPeer.setClientPortAddress(config.getClientPortAddress());
quorumPeer.setMinSessionTimeout(config.getMinSessionTimeout());
quorumPeer.setMaxSessionTimeout(config.getMaxSessionTimeout());
quorumPeer.setZKDatabase(new ZKDatabase(quorumPeer.getTxnFactory()));
quorumPeer.setLearnerType(config.getPeerType());
quorumPeer.setSyncEnabled(config.getSyncEnabled());
// sets quorum sasl authentication configurations
quorumPeer.setQuorumSaslEnabled(config.quorumEnableSasl);
if(quorumPeer.isQuorumSaslAuthEnabled()){quorumPeer.setQuorumServerSaslRequired(config.quorumServerRequireSasl);
quorumPeer.setQuorumLearnerSaslRequired(config.quorumLearnerRequireSasl);
quorumPeer.setQuorumServicePrincipal(config.quorumServicePrincipal);
quorumPeer.setQuorumServerLoginContext(config.quorumServerLoginContext);
quorumPeer.setQuorumLearnerLoginContext(config.quorumLearnerLoginContext);
}
quorumPeer.setQuorumCnxnThreadsSize(config.quorumCnxnThreadsSize);
quorumPeer.initialize();
quorumPeer.start();
quorumPeer.join();} catch (InterruptedException e) {
// warn, but generally this is ok
LOG.warn("Quorum Peer interrupted", e);
}
}能够从代码片段中能够看出, 新创建出了一个 QuorumPeer 对象, 其实这就是 OOP 思维, 以后实例代表着集群的一个节点, 而后将 QuorumPeerConfig 从新设置给 QuorumPeer 对象, 在这里呈现几个新的类：
| 类名 | 类形容 |
|---|---|
| FileTxnSnapLog | 长久化外围类别, 包含快照, 事务日志操作 |
| ServerCnxnFactory 3 | 服务端网络解决外围类, 其实现蕴含 NIO 和 Netty 两种实现 |
| ZKDatabase | 内存操作外围类, 通过树结构存储 |
在设置了参数之后, 接下来调用了 QuorumPeer#initialize 办法, 在这个办法里次要是一些鉴权类的对象实例化。外围还是 QuorumPeer#start 办法:
loadDataBase();// 将数据从快照和事务日志加载到内存中
cnxnFactory.start(); // 网络服务启动
startLeaderElection(); // 选举工作筹备
super.start(); loadDataBase:
在这个办法里次要是通过委托给 ZKDatabase#loadDataBase 进行加载工作的
public long loadDataBase() throws IOException {long zxid = snapLog.restore(dataTree, sessionsWithTimeouts, commitProposalPlaybackListener);
initialized = true;
return zxid;
} public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {snapLog.deserialize(dt, sessions); // 数据反序列化
return fastForwardFromEdits(dt, sessions, listener);
} public long deserialize(DataTree dt, Map<Long, Integer> sessions)
throws IOException {
// 找到无效的 100 个快照文件, 降序
List<File> snapList = findNValidSnapshots(100);
if (snapList.size() == 0) {return -1L;}
File snap = null;
boolean foundValid = false;
for (int i = 0; i < snapList.size(); i++) {snap = snapList.get(i);
InputStream snapIS = null;
CheckedInputStream crcIn = null;
try {LOG.info("Reading snapshot" + snap);
snapIS = new BufferedInputStream(new FileInputStream(snap));
crcIn = new CheckedInputStream(snapIS, new Adler32());
InputArchive ia = BinaryInputArchive.getArchive(crcIn);
// 真正序列化的中央
deserialize(dt,sessions, ia);
long checkSum = crcIn.getChecksum().getValue();
long val = ia.readLong("val");
// 校验快照文件的完整性
if (val != checkSum) {throw new IOException("CRC corruption in snapshot :" + snap);
}
foundValid = true;
break;
} catch(IOException e) {LOG.warn("problem reading snap file" + snap, e);
} finally {if (snapIS != null)
snapIS.close();
if (crcIn != null)
crcIn.close();}
}
if (!foundValid) {throw new IOException("Not able to find valid snapshots in" + snapDir);
}
// 快照文件命名为 snapshot.lastZxid
dt.lastProcessedZxid = Util.getZxidFromName(snap.getName(), SNAPSHOT_FILE_PREFIX);
return dt.lastProcessedZxid;
}在 ZkDataBase 里有一下几个外围属性:
| 表列 A | 表列 B |
|---|---|
| DataTree dataTree | 存储树结构 |
| FileTxnSnapLog snapLog | 事务快照长久化类别 |
| ,ConcurrentHashMap<Long, Integer> sessionsWithTimeouts | 会话治理,sessionId |
在 loadDataBase 办法中, 能够看到调用的 snapLog#restore 办法, 进入到 restore 办法中能够看到调用到的是 FileTxnSnapLog#deserialize 进行反序化, 而后保留到传入的 dt,sessions 参数中, 能够定位到 FileTxnSnapLog#deserialize(DataTree dt, Map<Long, Integer> sessions,
InputArchive ia)的这个重载办法来看下, 如何对快照文件进行反序列化的:
public void deserialize(DataTree dt, Map<Long, Integer> sessions,
InputArchive ia) throws IOException {FileHeader header = new FileHeader();
header.deserialize(ia, "fileheader");
if (header.getMagic() != SNAP_MAGIC) {
throw new IOException("mismatching magic headers"
+ header.getMagic() +
"!=" + FileSnap.SNAP_MAGIC);
}
首先通过文件输出流的包装类 InputArchive 进行读取, 调用的是 FileHeader#deserialize 办法：
public void deserialize(InputArchive a_, String tag) throws java.io.IOException {a_.startRecord(tag);
magic=a_.readInt("magic");
version=a_.readInt("version");
dbid=a_.readLong("dbid");
a_.endRecord(tag);
}FileHeader 实现 Record 接口, 其实前面所有须要的序列化和反序列化的都实现了这个接口, 通过传进来的输出流对象来自定义本人的序列化和反序列化细节.
在这里能够看到 FileHeader 的存储构造为:
| 属性值 | 占用大小 | 形容 |
|---|---|---|
| magic | 4 字节 | 魔法数字 |
| version | 4 字节 | 版本号 |
| version | 8 字节 | 数据库 id |
通过 FileHedare#deserialize 办法后, 曾经从文件流读取了 16 个字节, 接下来调用的是 SerializeUtils#deserializeSnapshot(dt,ia,sessions)进行其余内容的加载,
public static void deserializeSnapshot(DataTree dt,InputArchive ia,
Map<Long, Integer> sessions) throws IOException {
// 会话数量
int count = ia.readInt("count");
while (count > 0) {
// 会话 id
long id = ia.readLong("id");
// 会话超时工夫
int to = ia.readInt("timeout");
sessions.put(id, to);
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG, ZooTrace.SESSION_TRACE_MASK,
"loadData --- session in archive:" + id
+ "with timeout:" + to);
}
count--;
}
dt.deserialize(ia, "tree");
}能够看到首先是从流外面读取了 4 个字节的 count 属性, 也就是会话数量, 接着再遍历读取了 8 个字节 sessionId（会话 id）和 4 个字节的 timeout（会话超时工夫）, 再赋值个给了 sessions(也就是 ZkDataBase 的 sessionsWithTimeouts 属性), 最初调用的是 DataTree#deserialize 进行真正存储内容的反序列化工作：
public void deserialize(InputArchive ia, String tag) throws IOException {aclCache.deserialize(ia);
nodes.clear();
pTrie.clear();
String path = ia.readString("path");
while (!path.equals("/")) {DataNode node = new DataNode();
ia.readRecord(node, "node");
nodes.put(path, node);
synchronized (node) {aclCache.addUsage(node.acl);
}
int lastSlash = path.lastIndexOf('/');
if (lastSlash == -1) {root = node;} else {String parentPath = path.substring(0, lastSlash);
node.parent = nodes.get(parentPath);
if (node.parent == null) {
throw new IOException("Invalid Datatree, unable to find" +
"parent" + parentPath + "of path" + path);
}
node.parent.addChild(path.substring(lastSlash + 1));
long eowner = node.stat.getEphemeralOwner();
if (eowner != 0) {HashSet<String> list = ephemerals.get(eowner);
if (list == null) {list = new HashSet<String>();
ephemerals.put(eowner, list);
}
list.add(path);
}
}
path = ia.readString("path");
}
nodes.put("/", root);
setupQuota();
aclCache.purgeUnused();}- 网络传输(NIO)
zookeeper 与客户端建设连贯与申请与响应的数据传输都是通过 ServerCnxnFactory 这个类的实现类进行解决的, 咱们这里间接通过 NIO 的实现类 NIOServerCnxnFactory 来进行解说, 再 QuorumPeer 的 start 办法里咱们看到调用 NIOServerCnxnFactory#start 办法.
public void start() {
// ensure thread is started once and only once
if (thread.getState() == Thread.State.NEW) {thread.start();
}
}再 start 办法里咱们看到就简略调用了 Thread#start 办法启动线程. 至于 thread 办法是在哪里进行初始化的, 我能够定位到 NIOServerCnxnFactory#configure 办法里：
public void configure(InetSocketAddress addr, int maxcc) throws IOException {configureSaslLogin();
// 初始化线程对象
thread = new ZooKeeperThread(this, "NIOServerCxn.Factory:" + addr);
thread.setDaemon(true);
// 设置最大连接数参数
maxClientCnxns = maxcc;
// 初始化 Socket 相干配置
this.ss = ServerSocketChannel.open();
ss.socket().setReuseAddress(true);
LOG.info("binding to port" + addr);
ss.socket().bind(addr);
ss.configureBlocking(false);
ss.register(selector, SelectionKey.OP_ACCEPT);
}-
选举
在进启动了网络传输服务之后, 就开始筹备着选举前的一些筹备工作, 咱们能够从 QuorumPeer#start 办法中的 QuorumPeer#startLeaderElection()调用进行一个选举的切入点:synchronized public void startLeaderElection() { try { // 设置初始化投票 currentVote = new Vote(myid, getLastLoggedZxid(), getCurrentEpoch()); } catch(IOException e) {RuntimeException re = new RuntimeException(e.getMessage()); re.setStackTrace(e.getStackTrace()); throw re; } for (QuorumServer p : getView().values()) {if (p.id == myid) { myQuorumAddr = p.addr; break; } } if (myQuorumAddr == null) {throw new RuntimeException("My id" + myid + "not in the peer list"); } if (electionType == 0) { try {udpSocket = new DatagramSocket(myQuorumAddr.getPort()); // 启动响应线程 responder = new ResponderThread(); responder.start();} catch (SocketException e) {throw new RuntimeException(e); } } // 依据配置的选举算法进行一些初始化工作 this.electionAlg = createElectionAlgorithm(electionType); }从 startLeaderElection 这个办法中能够看出, 次要是将初始化投票设置为本身,sid 为本身 serverId,zxid 为通过快照和事务日志加载后的最大 lastZxid, 还有 peerEpoch(选举年代)也就是以后本身的选举年代, 而后就是启动了 ReponseThread 这个响应线程, 外围逻辑还是在 createElectionAlgorithm 这个办法中, 咱们能够跟进去看一下具体的代码逻辑:
protected Election createElectionAlgorithm(int electionAlgorithm){
Election le=null;
//TODO: use a factory rather than a switch
switch (electionAlgorithm) {
case 0:
le = new LeaderElection(this);
break;
case 1:
// 已过期
le = new AuthFastLeaderElection(this);
break;
case 2:
// 已过期
le = new AuthFastLeaderElection(this, true);
break;
case 3:
// 创立连贯管理器
qcm = createCnxnManager();
QuorumCnxManager.Listener listener = qcm.listener;
if(listener != null){
// 启动监听其余节点的连贯申请
listener.start();
// 实例化疾速选举算法外围类
le = new FastLeaderElection(this, qcm);
} else {LOG.error("Null listener when initializing cnx manager");
}
break;
default:
assert false;
}
return le;
}从上述代码中, 能够看出次要工作是实例化了一个 QuorumCnxManager 这个对象, 也就是通过这个对象中的 Listener 这个类来解决和其余节点的连贯申请, 调用了 Listener#start 办法理论是运行到了 Listener#run 办法代码中:
public void run() {
int numRetries = 0;
InetSocketAddress addr;
while((!shutdown) && (numRetries < 3)){
try {
// 实例化 ServerSocket
ss = new ServerSocket();
ss.setReuseAddress(true);
if (listenOnAllIPs) {int port = view.get(QuorumCnxManager.this.mySid)
.electionAddr.getPort();
addr = new InetSocketAddress(port);
} else {addr = view.get(QuorumCnxManager.this.mySid)
.electionAddr;
}
LOG.info("My election bind port:" + addr.toString());
setName(view.get(QuorumCnxManager.this.mySid)
.electionAddr.toString());
ss.bind(addr);
while (!shutdown) {
// 阻塞期待其余节点申请连贯
Socket client = ss.accept();
setSockOpts(client);
LOG.info("Received connection request"
+ client.getRemoteSocketAddress());
if (quorumSaslAuthEnabled) {receiveConnectionAsync(client);
} else {
// 承受申请外围逻辑
receiveConnection(client);
}
numRetries = 0;
}
} catch (IOException e) {LOG.error("Exception while listening", e);
numRetries++;
try {ss.close();
Thread.sleep(1000);
} catch (IOException ie) {LOG.error("Error closing server socket", ie);
} catch (InterruptedException ie) {
LOG.error("Interrupted while sleeping." +
"Ignoring exception", ie);
}
}
}
LOG.info("Leaving listener");
if (!shutdown) {
LOG.error("As I'm leaving the listener thread, "+"I won't be able to participate in leader"
+ "election any longer:"
+ view.get(QuorumCnxManager.this.mySid).electionAddr);
}
}该办法次要是应用 jdk 的阻塞 io 与其余节点建设连贯, 不理解的能够去自行补充一下 jdk 的 socket 编程基础知识, 在第二个 while 循环中的 ss.accept()代码是会始终阻塞期待其余节点申请连贯, 当其余节点建设连贯后, 就会返回一个 Socket 实例, 而后将 Socket 实例传入 receiveConnection 办法中, 而后咱们就能够和其余节点进行通信了, 具体 receiveConnection 代码逻辑如下:
public void receiveConnection(final Socket sock) {
DataInputStream din = null;
try {
// 将输出流进行屡次包装
din = new DataInputStream(new BufferedInputStream(sock.getInputStream()));
// 真正解决连贯
handleConnection(sock, din);
} catch (IOException e) {LOG.error("Exception handling connection, addr: {}, closing server connection",
sock.getRemoteSocketAddress());
closeSocket(sock);
}
}将 io 输出流包装后, 进一步调用了 handleConnection 进行连贯的解决:
private void handleConnection(Socket sock, DataInputStream din)
throws IOException {
Long sid = null;
try {
// 阻塞期待另外一个节点发送建设申请的第一个包
// 先读取 8 个字节, 又可能 sid（服务 id）, 也有可能是 protocolVersion（协定版本）sid = din.readLong();
// 读取到的是协定版本
if (sid < 0) {
// 进一步读取 8 个字节, 就是真正的 sid
sid = din.readLong();
// 读取 4 个字节, 也就是读取到的是残余的其余内容的字节数
int num_remaining_bytes = din.readInt();
// 进行字数校验
if (num_remaining_bytes < 0 || num_remaining_bytes > maxBuffer) {LOG.error("Unreasonable buffer length: {}", num_remaining_bytes);
closeSocket(sock);
return;
}
byte[] b = new byte[num_remaining_bytes];
// 一次性将所有剩下的字节内容读取到 b 这个字节数组中
int num_read = din.read(b);
if (num_read != num_remaining_bytes) {LOG.error("Read only" + num_read + "bytes out of" + num_remaining_bytes + "sent by server" + sid);
}
}
if (sid == QuorumPeer.OBSERVER_ID) {sid = observerCounter.getAndDecrement();
LOG.info("Setting arbitrary identifier to observer:" + sid);
}
} catch (IOException e) {closeSocket(sock);
LOG.warn("Exception reading or writing challenge:" + e.toString());
return;
}
LOG.debug("Authenticating learner server.id: {}", sid);
authServer.authenticate(sock, din);
// 如果读取的 sid 小于以后节点的 sid, 则敞开之前建设过的连贯
if (sid < this.mySid) {SendWorker sw = senderWorkerMap.get(sid);
if (sw != null) {sw.finish();
}
LOG.debug("Create new connection to server:" + sid);
closeSocket(sock);
// 敞开之前的连贯后, 由以后节点发动连贯申请
connectOne(sid);
} else {
// 发送线程
SendWorker sw = new SendWorker(sock, sid);
// 承受线程
RecvWorker rw = new RecvWorker(sock, din, sid, sw);
sw.setRecv(rw);
SendWorker vsw = senderWorkerMap.get(sid);
if(vsw != null)
vsw.finish();
senderWorkerMap.put(sid, sw);
queueSendMap.putIfAbsent(sid, new ArrayBlockingQueue<ByteBuffer>(SEND_CAPACITY));
// 启动发送线程
sw.start();
// 启动承受线程
rw.start();
return;
}
}从这段代码中能够看出, 建设申请只能由 sid 大的一方发动, 由 sid 小的一方承受, 如当初有 sid=1,sid=2,sid= 3 三个节点, 那么只能由 2 这个节点发动连贯申请,1 这个这个节点解决连贯申请. 这样就保障了单方只放弃着一条连贯, 因为 Socket 是全双工模式, 反对单方进行通信.Socket 能够通过 ss.accept 获取到, 还能够通过以后办法的 connectOne 这个办法去和 sid 较小的节点进行连贯：
synchronized public void connectOne(long sid){
// 就是判断 sendWorkerMap 中是否蕴含了以后 sid
if (!connectedToPeer(sid)){
InetSocketAddress electionAddr;
if (view.containsKey(sid)) {
// 拿到之前配置的 server.id 的选举地址
electionAddr = view.get(sid).electionAddr;
} else {LOG.warn("Invalid server id:" + sid);
return;
}
try {LOG.debug("Opening channel to server" + sid);
// 实例化 Socket 对象
Socket sock = new Socket();
setSockOpts(sock);
// 进行连贯
sock.connect(view.get(sid).electionAddr, cnxTO);
LOG.debug("Connected to server" + sid);
if (quorumSaslAuthEnabled) {initiateConnectionAsync(sock, sid);
} else {
// 同步初始化连贯, 也就是将以后本身的一些信息发送给其余节点
initiateConnection(sock, sid);
}
} catch (UnresolvedAddressException e) {
LOG.warn("Cannot open channel to" + sid
+ "at election address" + electionAddr, e);
if (view.containsKey(sid)) {view.get(sid).recreateSocketAddresses();}
throw e;
} catch (IOException e) {
LOG.warn("Cannot open channel to" + sid
+ "at election address" + electionAddr,
e);
if (view.containsKey(sid)) {view.get(sid).recreateSocketAddresses();}
}
} else {LOG.debug("There is a connection already for server" + sid);
}
} public void initiateConnection(final Socket sock, final Long sid) {
try {startConnection(sock, sid);
} catch (IOException e) {LOG.error("Exception while connecting, id: {}, addr: {}, closing learner connection",
new Object[] { sid, sock.getRemoteSocketAddress() }, e);
closeSocket(sock);
return;
}
} private boolean startConnection(Socket sock, Long sid)
throws IOException {
DataOutputStream dout = null;
DataInputStream din = null;
try {dout = new DataOutputStream(sock.getOutputStream());
// 将本身 sid 发送给其余节点
dout.writeLong(this.mySid);
dout.flush();
din = new DataInputStream(new BufferedInputStream(sock.getInputStream()));
} catch (IOException e) {LOG.warn("Ignoring exception reading or writing challenge:", e);
closeSocket(sock);
return false;
}
// authenticate learner
authLearner.authenticate(sock, view.get(sid).hostname);
if (sid > this.mySid) {
LOG.info("Have smaller server identifier, so dropping the" +
"connection: (" + sid + "," + this.mySid + ")");
closeSocket(sock);
// Otherwise proceed with the connection
} else {
// 以下逻辑就和通过 ss.accept 拿到 socket 对象之后一样的逻辑
SendWorker sw = new SendWorker(sock, sid);
RecvWorker rw = new RecvWorker(sock, din, sid, sw);
sw.setRecv(rw);
SendWorker vsw = senderWorkerMap.get(sid);
if(vsw != null)
vsw.finish();
senderWorkerMap.put(sid, sw);
queueSendMap.putIfAbsent(sid, new ArrayBlockingQueue<ByteBuffer>(SEND_CAPACITY));
sw.start();
rw.start();
return true;
}
return false;
}从以上几个办法中能够看出, 在通过 ServerSocket.accpet 和 socket.connect 拿到了 Socket 对象之后, 实例化进去一个 SendWorker 和一个 RecvWorker 这个对象, 并调用了各自的 start 办法去启动两个线程, 其实就是通过这 2 个线程去实现和其余节点的申请和响应的数据传输工作, 一 个节点保护一个 SendWorker、一个 RecvWorker 和通过 queueSendMap 来存储一个队列来进行通信的。
具体前面这 3 个对象是如何发挥作用的, 会在选举细节中具体解说. 实现这一系列的选举筹备工作后, 咱们回到 QuorumPeer#start 办法中, 接下来 QuorumPeer#start 办法调用 super.start()办法, 因为 QuorumPeer 这个对象继承了 ZooKeeperThread, 而 ZooKeeperThread 又继承了 jdk 的 Thread 类, 所以调用了 super.start 之后, 就会独自开拓一个线程去执行 QuorumPeer#run 办法, 也就是真正进行选举的中央:
public void run() {setName("QuorumPeer" + "[myid=" + getId() + "]" +
cnxnFactory.getLocalAddress());
LOG.debug("Starting quorum peer");
//1.jmx 拓展点
try {jmxQuorumBean = new QuorumBean(this);
MBeanRegistry.getInstance().register(jmxQuorumBean, null);
for(QuorumServer s: getView().values()){
ZKMBeanInfo p;
if (getId() == s.id) {p = jmxLocalPeerBean = new LocalPeerBean(this);
try {MBeanRegistry.getInstance().register(p, jmxQuorumBean);
} catch (Exception e) {LOG.warn("Failed to register with JMX", e);
jmxLocalPeerBean = null;
}
} else {p = new RemotePeerBean(s);
try {MBeanRegistry.getInstance().register(p, jmxQuorumBean);
} catch (Exception e) {LOG.warn("Failed to register with JMX", e);
}
}
}
} catch (Exception e) {LOG.warn("Failed to register with JMX", e);
jmxQuorumBean = null;
}
2.// 选举逻辑
try {
/*
* Main loop
*/
while (running) {switch (getPeerState()) {
//1.Looking 状态
case LOOKING:
LOG.info("LOOKING");
// 开启只读模式
if (Boolean.getBoolean("readonlymode.enabled")) {LOG.info("Attempting to start ReadOnlyZooKeeperServer");
final ReadOnlyZooKeeperServer roZk = new ReadOnlyZooKeeperServer(
logFactory, this,
new ZooKeeperServer.BasicDataTreeBuilder(),
this.zkDb);
Thread roZkMgr = new Thread() {public void run() {
try {
// lower-bound grace period to 2 secs
sleep(Math.max(2000, tickTime));
if (ServerState.LOOKING.equals(getPeerState())) {roZk.startup();
}
} catch (InterruptedException e) {LOG.info("Interrupted while attempting to start ReadOnlyZooKeeperServer, not started");
} catch (Exception e) {LOG.error("FAILED to start ReadOnlyZooKeeperServer", e);
}
}
};
try {roZkMgr.start();
setBCVote(null);
setCurrentVote(makeLEStrategy().lookForLeader());
} catch (Exception e) {LOG.warn("Unexpected exception",e);
setPeerState(ServerState.LOOKING);
} finally {
// If the thread is in the the grace period, interrupt
// to come out of waiting.
roZkMgr.interrupt();
roZk.shutdown();}
} else {
try {setBCVote(null);
// 调用 ElectionAlg#lookForLeader 办法, 而后返回选举后的投票信息
setCurrentVote(makeLEStrategy().lookForLeader());
} catch (Exception e) {LOG.warn("Unexpected exception", e);
setPeerState(ServerState.LOOKING);
}
}
break;
// 选举完结,observer 角色进如到此处
case OBSERVING:
try {LOG.info("OBSERVING");
setObserver(makeObserver(logFactory));
observer.observeLeader();} catch (Exception e) {LOG.warn("Unexpected exception",e);
} finally {observer.shutdown();
setObserver(null);
setPeerState(ServerState.LOOKING);
}
break;
// 选举完结,Follower 角色进入到此
case FOLLOWING:
try {LOG.info("FOLLOWING");
setFollower(makeFollower(logFactory));
follower.followLeader();} catch (Exception e) {LOG.warn("Unexpected exception",e);
} finally {follower.shutdown();
setFollower(null);
setPeerState(ServerState.LOOKING);
}
break;
// 选举完结,Leader 角色进入到此
case LEADING:
LOG.info("LEADING");
try {setLeader(makeLeader(logFactory));
leader.lead();
setLeader(null);
} catch (Exception e) {LOG.warn("Unexpected exception",e);
} finally {if (leader != null) {leader.shutdown("Forcing shutdown");
setLeader(null);
}
setPeerState(ServerState.LOOKING);
}
break;
}
}
} finally {LOG.warn("QuorumPeer main thread exited");
try {MBeanRegistry.getInstance().unregisterAll();} catch (Exception e) {LOG.warn("Failed to unregister with JMX", e);
}
jmxQuorumBean = null;
jmxLocalPeerBean = null;
}
}咱们能够从上诉代码中的 MainLoop 处开始看, 进入 while 循环后, 因为以后节点还是 looking 状态, 苏所以进入到 looking 分支, 在这个分支中能够看到首先判断以后节点是否是只读模式, 因为以后不解说只读模式, 所以间接进入到另外一个分支：
setBCVote(null);
// 调用 ElectionAlg#lookForLeader 办法, 而后返回选举后的投票信息
setCurrentVote(makeLEStrategy().lookForLeader());makeLEStrategy 办法返回的其实就是咱们在 QuorumPeer#startLeaderElection 办法中实例话进去的 FastLeaderElection 实例, 而后调用 FastLeaderElection#lookForLeader 办法进行 Leader 选举:
public Vote lookForLeader() throws InterruptedException {
try {self.jmxLeaderElectionBean = new LeaderElectionBean();
MBeanRegistry.getInstance().register(self.jmxLeaderElectionBean, self.jmxLocalPeerBean);
} catch (Exception e) {LOG.warn("Failed to register with JMX", e);
self.jmxLeaderElectionBean = null;
}
if (self.start_fle == 0) {self.start_fle = Time.currentElapsedTime();
}
try {HashMap<Long, Vote> recvset = new HashMap<Long, Vote>();
HashMap<Long, Vote> outofelection = new HashMap<Long, Vote>();
int notTimeout = finalizeWait;
synchronized(this){logicalclock.incrementAndGet();
updateProposal(getInitId(), getInitLastLoggedZxid(), getPeerEpoch());
}
LOG.info("New election. My id =" + self.getId() +
", proposed zxid=0x" + Long.toHexString(proposedZxid));
sendNotifications();
/*
* Loop in which we exchange notifications until we find a leader
*/
while ((self.getPeerState() == ServerState.LOOKING) &&
(!stop)){
/*
* Remove next notification from queue, times out after 2 times
* the termination time
*/
Notification n = recvqueue.poll(notTimeout,
TimeUnit.MILLISECONDS);
/*
* Sends more notifications if haven't received enough.
* Otherwise processes new notification.
*/
if(n == null){if(manager.haveDelivered()){sendNotifications();
} else {manager.connectAll();
}
/*
* Exponential backoff
*/
int tmpTimeOut = notTimeout*2;
notTimeout = (tmpTimeOut < maxNotificationInterval?
tmpTimeOut : maxNotificationInterval);
LOG.info("Notification time out:" + notTimeout);
}
else if(validVoter(n.sid) && validVoter(n.leader)) {
/*
* Only proceed if the vote comes from a replica in the
* voting view for a replica in the voting view.
*/
switch (n.state) {
case LOOKING:
// If notification > current, replace and send messages out
if (n.electionEpoch > logicalclock.get()) {logicalclock.set(n.electionEpoch);
recvset.clear();
if(totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
getInitId(), getInitLastLoggedZxid(), getPeerEpoch())) {updateProposal(n.leader, n.zxid, n.peerEpoch);
} else {updateProposal(getInitId(),
getInitLastLoggedZxid(),
getPeerEpoch());
}
sendNotifications();} else if (n.electionEpoch < logicalclock.get()) {if(LOG.isDebugEnabled()){
LOG.debug("Notification election epoch is smaller than logicalclock. n.electionEpoch = 0x"
+ Long.toHexString(n.electionEpoch)
+ ", logicalclock=0x" + Long.toHexString(logicalclock.get()));
}
break;
} else if (totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
proposedLeader, proposedZxid, proposedEpoch)) {updateProposal(n.leader, n.zxid, n.peerEpoch);
sendNotifications();}
if(LOG.isDebugEnabled()){
LOG.debug("Adding vote: from=" + n.sid +
", proposed leader=" + n.leader +
", proposed zxid=0x" + Long.toHexString(n.zxid) +
", proposed election epoch=0x" + Long.toHexString(n.electionEpoch));
}
recvset.put(n.sid, new Vote(n.leader, n.zxid, n.electionEpoch, n.peerEpoch));
if (termPredicate(recvset,
new Vote(proposedLeader, proposedZxid,
logicalclock.get(), proposedEpoch))) {
// Verify if there is any change in the proposed leader
while((n = recvqueue.poll(finalizeWait,
TimeUnit.MILLISECONDS)) != null){
if(totalOrderPredicate(n.leader, n.zxid, n.peerEpoch,
proposedLeader, proposedZxid, proposedEpoch)){recvqueue.put(n);
break;
}
}
/*
* This predicate is true once we don't read any new
* relevant message from the reception queue
*/
if (n == null) {self.setPeerState((proposedLeader == self.getId()) ?
ServerState.LEADING: learningState());
Vote endVote = new Vote(proposedLeader,
proposedZxid,
logicalclock.get(),
proposedEpoch);
leaveInstance(endVote);
return endVote;
}
}
break;
case OBSERVING:
LOG.debug("Notification from observer:" + n.sid);
break;
case FOLLOWING:
case LEADING:
/*
* Consider all notifications from the same epoch
* together.
*/
if(n.electionEpoch == logicalclock.get()){
recvset.put(n.sid, new Vote(n.leader,
n.zxid,
n.electionEpoch,
n.peerEpoch));
if(ooePredicate(recvset, outofelection, n)) {self.setPeerState((n.leader == self.getId()) ?
ServerState.LEADING: learningState());
Vote endVote = new Vote(n.leader,
n.zxid,
n.electionEpoch,
n.peerEpoch);
leaveInstance(endVote);
return endVote;
}
}
/*
* Before joining an established ensemble, verify
* a majority is following the same leader.
*/
outofelection.put(n.sid, new Vote(n.version,
n.leader,
n.zxid,
n.electionEpoch,
n.peerEpoch,
n.state));
if(ooePredicate(outofelection, outofelection, n)) {synchronized(this){logicalclock.set(n.electionEpoch);
self.setPeerState((n.leader == self.getId()) ?
ServerState.LEADING: learningState());
}
Vote endVote = new Vote(n.leader,
n.zxid,
n.electionEpoch,
n.peerEpoch);
leaveInstance(endVote);
return endVote;
}
break;
default:
LOG.warn("Notification state unrecognized: {} (n.state), {} (n.sid)",
n.state, n.sid);
break;
}
} else {if (!validVoter(n.leader)) {LOG.warn("Ignoring notification for non-cluster member sid {} from sid {}", n.leader, n.sid);
}
if (!validVoter(n.sid)) {LOG.warn("Ignoring notification for sid {} from non-quorum member sid {}", n.leader, n.sid);
}
}
}
return null;
} finally {
try {if(self.jmxLeaderElectionBean != null){MBeanRegistry.getInstance().unregister(self.jmxLeaderElectionBean);
}
} catch (Exception e) {LOG.warn("Failed to unregister with JMX", e);
}
self.jmxLeaderElectionBean = null;
LOG.debug("Number of connection processing threads: {}",
manager.getConnectionThreadCount());
}
}未完待续 …….