一.源码仓库:
zookeeper
基于分支3.4.14分支在windows系统启动流程进行分析。
二.流程分析:
- 源码入口
通过zkServer.cmd可执行文件内容可以看出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方法传入的是我们zoo.cfg文件的地址,然后通过解析zoo.cfg文件,将key,value的配置信息转换成QuorumPeerConfig的对象,转换细节可以看QuorumPeerConfig.parse方法,其中转换后的核心配置参数有:
| 参数名 | 参数描述 |
|---|---|
| dataLogDir | 事务日志存储路径 |
| dataDir | 快照存储路径 |
| electionType | 选举算法,目前只支持3-快速选举算法 |
| myid | 当前服务id |
| tickTime | 时间单位 |
| initLimit | |
| syncLimit | 事务存储路径 |
| minSessionTimeout | 最小会话超时时间 |
| maxSessionTimeout | 最大会话超时时间 |
| peerType | 角色类型-OBSERVER,PARTICIPANT |
| clientPort | 客户端连接端口 |
| clientPortAddress | 客户端连接Host |
| snapRetainCount | 快照保留个数,最小为3 |
| purgeInterval | 快照清除间隔 |
| 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,可以通过是否配置了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方法启动,集群启动则还是在QuorumPeerMain#runFromConfig方法进行处理的,这里我们就直接讲解集群模式,因为集群模式比单机模式多了集群间的通信相关的处理,如Leader选举,数据同步,请求转发等.
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);
}
}可以从代码片段中可以看出,新创建出了一个QuorumPeer对象,其实这就是OOP思想,当前实例代表着集群的一个节点,然后将QuorumPeerConfig重新设置给QuorumPeer对象,在这里出现几个新的类：
| 类名 | 类描述 |
|---|---|
| FileTxnSnapLog | 持久化核心类别,包括快照,事务日志操作 |
| ServerCnxnFactory 3 | 服务端网络处理核心类,其实现包含NIO和Netty两种实现 |
| ZKDatabase | 内存操作核心类,通过树结构存储 |
在设置了参数之后,接下来调用了QuorumPeer#initialize方法,在这个方法里主要是一些鉴权类的对象实例化。核心还是QuorumPeer#start方法:
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(); //选举工作准备
super.start(); loadDataBase:
在这个方法里主要是通过委托给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 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 sessions)
throws IOException {
//找到有效的100个快照文件,降序
List 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);
//真正序列化的地方
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里有一下几个核心属性:
| 表列 A | 表列 B |
|---|---|
| DataTree dataTree | 存储树结构 |
| FileTxnSnapLog snapLog | 事务快照持久化类别 |
| ,ConcurrentHashMap |
会话管理,sessionId |
在loadDataBase方法中,可以看到调用的snapLog#restore方法,进入到restore方法中可以看到调用到的是FileTxnSnapLog#deserialize进行反序化,然后保存到传入的dt,sessions参数中,可以定位到FileTxnSnapLog#deserialize(DataTree dt, Map
InputArchive ia)的这个重载方法来看下,如何对快照文件进行反序列化的:
public void deserialize(DataTree dt, Map 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);
}
首先通过文件输入流的包装类InputArchive进行读取,调用的是FileHeader#deserialize方法：
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,其实后面所有需要的序列化和反序列化的都实现了这个接口,通过传进来的输入流对象来自定义自己的序列化和反序列化细节.
在这里可以看到FileHeader的存储结构为:
| 属性值 | 占用大小 | 描述 |
|---|---|---|
| magic | 4字节 | 魔法数字 |
| version | 4字节 | 版本号 |
| version | 8字节 | 数据库id |
经过FileHedare#deserialize方法后,已经从文件流读取了16个字节,接下来调用的是 SerializeUtils#deserializeSnapshot(dt,ia,sessions)进行其他内容的加载,
public static void deserializeSnapshot(DataTree dt,InputArchive ia,
Map sessions) throws IOException {
//会话数量
int count = ia.readInt("count");
while (count > 0) {
//会话id
long id = ia.readLong("id");
//会话超时时间
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");
} 可以看到首先是从流里面读取了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（会话超时时间）,再赋值个给了sessions(也就是ZkDataBase的sessionsWithTimeouts属性),最后调用的是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 list = ephemerals.get(eowner);
if (list == null) {
list = new HashSet();
ephemerals.put(eowner, list);
}
list.add(path);
}
}
path = ia.readString("path");
}
nodes.put("/", root);
setupQuota();
aclCache.purgeUnused();
} - 网络传输(NIO)
zookeeper与客户端建立连接与请求与响应的数据传输都是通过ServerCnxnFactory这个类的实现类进行处理的,我们这里直接通过NIO的实现类NIOServerCnxnFactory来进行讲解,再QuorumPeer的start方法里我们看到调用NIOServerCnxnFactory#start方法.
public void start() {
// ensure thread is started once and only once
if (thread.getState() == Thread.State.NEW) {
thread.start();
}
}再start方法里我们看到就简单调用了Thread#start方法启动线程.至于thread方法是在哪里进行初始化的,我可以定位到NIOServerCnxnFactory#configure方法里：
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相关配置
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,就开始准备着选举前的一些准备工作,我们可以从QuorumPeer#start方法中的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); } } //根据配置的选举算法进行一些初始化工作 this.electionAlg = createElectionAlgorithm(electionType); }从startLeaderElection这个方法中可以看出,主要是将初始化投票设置为自身,sid为自身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)也就是当前自身的选举年代,然后就是启动了ReponseThread这个响应线程,核心逻辑还是在createElectionAlgorithm这个方法中,我们可以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:
//已过时
le = new AuthFastLeaderElection(this);
break;
case 2:
//已过时
le = new AuthFastLeaderElection(this, true);
break;
case 3:
//创建连接管理器
qcm = createCnxnManager();
QuorumCnxManager.Listener listener = qcm.listener;
if(listener != null){
//启动监听其他节点的连接请求
listener.start();
//实例化快速选举算法核心类
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,可以看出主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这个类来处理和其他节点的连接请求,调用了Listener#start方法实际是运行到了Listener#run方法代码中:
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) {
//阻塞等待其他节点请求连接
Socket client = ss.accept();
setSockOpts(client);
LOG.info("Received connection request "
+ client.getRemoteSocketAddress());
if (quorumSaslAuthEnabled) {
receiveConnectionAsync(client);
} else {
//接受请求核心逻辑
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);
}
}该方法主要是使用jdk的阻塞io与其他节点建立连接,不了解的可以去自行补充一下jdk的socket编程基础知识,在第二个while循环中的ss.accept()代码是会一直阻塞等待其他节点请求连接,当其他节点建立连接后,就会返回一个Socket实例,然后将Socket实例传入receiveConnection方法中,然后我们就可以和其他节点进行通信了,具体receiveConnection代码逻辑如下:
public void receiveConnection(final Socket sock) {
DataInputStream din = null;
try {
//将输入流进行多次包装
din = new DataInputStream(
new BufferedInputStream(sock.getInputStream()));
//真正处理连接
handleConnection(sock, din);
} catch (IOException e) {
LOG.error("Exception handling connection, addr: {}, closing server connection",
sock.getRemoteSocketAddress());
closeSocket(sock);
}
}将io输入流包装后,进一步调用了handleConnection进行连接的处理:
private void handleConnection(Socket sock, DataInputStream din)
throws IOException {
Long sid = null;
try {
// 阻塞等待另外一个节点发送建立请求的第一个包
//先读取8个字节,又可能sid（服务id）,也有可能是protocolVersion（协议版本）
sid = din.readLong();
//读取到的是协议版本
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,也就是读取到的是剩余的其他内容的字节数
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小于当前节点的sid,则关闭之前建立过的连接
if (sid < this.mySid) {
SendWorker sw = senderWorkerMap.get(sid);
if (sw != null) {
sw.finish();
}
LOG.debug("Create new connection to server: " + sid);
closeSocket(sock);
//关闭之前的连接后,由当前节点发起连接请求
connectOne(sid);
} else {
//发送线程
SendWorker sw = new SendWorker(sock, sid);
//接受线程
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(SEND_CAPACITY));
//启动发送线程
sw.start();
//启动接受线程
rw.start();
return;
}
} 从这段代码中可以看出,建立请求只能由sid大的一方发起,由sid小的一方接受,如现在有sid=1,sid=2,sid=3三个节点,那么只能由2这个节点发起连接请求,1这个这个节点处理连接请求.这样就保证了双方只保持着一条连接,因为Socket是全双工模式,支持双方进行通信.Socket可以通过ss.accept获取到,还可以通过当前方法的connectOne这个方法去和sid较小的节点进行连接：
synchronized public void connectOne(long sid){
//就是判断sendWorkerMap中是否包含了当前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);
//进行连接
sock.connect(view.get(sid).electionAddr, cnxTO);
LOG.debug("Connected to server " + sid);
if (quorumSaslAuthEnabled) {
initiateConnectionAsync(sock, sid);
} else {
//同步初始化连接,也就是将当前自身的一些信息发送给其他节点
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());
//将自身sid发送给其他节点
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(SEND_CAPACITY));
sw.start();
rw.start();
return true;
}
return false;
} 从以上几个方法中可以看出,在通过ServerSocket.accpet和socket.connect拿到了Socket对象之后,实例化出来一个SendWorker和一个RecvWorker这个对象,并调用了各自的start方法去启动两个线程,其实就是通过这2个线程去完成和其他节点的请求和响应的数据传输工作,一个节点维护一个SendWorker、一个RecvWorker和通过queueSendMap来存储一个队列来进行通信的。
具体后面这3个对象是如何发挥作用的,会在选举细节中具体讲解.完成这一系列的选举准备工作后,我们回到QuorumPeer#start方法中,接下来QuorumPeer#start方法调用super.start()方法,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,就会单独开辟一个线程去执行QuorumPeer#run方法,也就是真正进行选举的地方:
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方法,然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;
//选举结束,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;
//选举结束,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;
//选举结束,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;
}
}我们可以从上诉代码中的MainLoop处开始看,进入while循环后,因为当前节点还是looking状态,苏所以进入到looking分支,在这个分支中可以看到首先判断当前节点是否是只读模式,因为当前不讲解只读模式,所以直接进入到另外一个分支：
setBCVote(null);
//调用ElectionAlg#lookForLeader方法,然后返回选举后的投票信息
setCurrentVote(makeLEStrategy().lookForLeader());makeLEStrategy方法返回的其实就是我们在QuorumPeer#startLeaderElection方法中实例话出来的FastLeaderElection实例,然后调用FastLeaderElection#lookForLeader方法进行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 recvset = new HashMap();
HashMap outofelection = new HashMap();
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.......