zookeeper启动过程-粗略梳理

zookeeper 3.4.6
=========
启动脚本里面
```
nohup "$JAVA" "-Dzookeeper.log.dir=${ZOO_LOG_DIR}" "-Dzookeeper.root.logger=${ZOO_LOG4J_PROP}" \ -cp "$CLASSPATH" $JVMFLAGS $ZOOMAIN "$ZOOCFG" > "$_ZOO_DAEMON_OUT" 2>&1 < /dev/null &
```
翻译过来之后太烦了,shit
```
java -Dzookeeper.log.dir=. -Dzookeeper.root.logger=INFO,CONSOLE -cp /usr/local/luping/zookeeper-3.4.6/bin/../build/classes:/usr/local/luping/zookeeper-3.4.6/bin/../build/lib/*.jar:/usr/local/luping/zookeeper-3.4.6/bin/../lib/slf4j-log4j12-1.6.1.jar:/usr/local/luping/zookeeper-3.4.6/bin/../lib/slf4j-api-1.6.1.jar:/usr/local/luping/zookeeper-3.4.6/bin/../lib/netty-3.7.0.Final.jar:/usr/local/luping/zookeeper-3.4.6/bin/../lib/log4j-1.2.16.jar:/usr/local/luping/zookeeper-3.4.6/bin/../lib/jline-0.9.94.jar:/usr/local/luping/zookeeper-3.4.6/bin/../zookeeper-3.4.6.jar:/usr/local/luping/zookeeper-3.4.6/bin/../src/java/lib/*.jar:/usr/local/luping/zookeeper-3.4.6/bin/../conf:.:/data/java/jdk1.7.0_15/jre/lib/rt.jar:/data/java/jdk1.7.0_15/lib/dt.jar:/data/java/jdk1.7.0_15/lib/tools.jar -Dcom.sun.management.jmxremote -Dcom.sun.management.jmxremote.local.only=false org.apache.zookeeper.server.quorum.QuorumPeerMain
/usr/local/luping/zookeeper-3.4.6/bin/../conf/zoo.cfg
```
这里看到启动入口是QuorumPeerMain，先看其main（）函数关键代码
```
QuorumPeerMain main = new QuorumPeerMain();
main.initializeAndRun(args);
```
initializeAndRun（）这种会启动单例还是集群模式的zookeeper
```
protected void initializeAndRun(String[] args)
throws ConfigException, IOException
{
QuorumPeerConfig config = new QuorumPeerConfig();
if (args.length == 1) {
config.parse(args[0]);
}

// Start and schedule the the purge task
DatadirCleanupManager purgeMgr = new DatadirCleanupManager(config
.getDataDir(), config.getDataLogDir(), config
.getSnapRetainCount(), config.getPurgeInterval());
purgeMgr.start();

if (args.length == 1 && config.servers.size() > 0) {
runFromConfig(config);
} else {
LOG.warn("Either no config or no quorum defined in config, running "
+ " in standalone mode");
// there is only server in the quorum -- run as standalone
ZooKeeperServerMain.main(args);
}
}
```
这里如果是集群模式走runFromConfig，首先注册Mxbean
```
ManagedUtil.registerLog4jMBeans();
```
然后是初始化连接工厂，默认使用NIO,这里是NIOServerCnxnFactory
```
ServerCnxnFactory cnxnFactory = ServerCnxnFactory.createFactory();
cnxnFactory.configure(config.getClientPortAddress(),
config.getMaxClientCnxns());
```
```
static public ServerCnxnFactory createFactory() throws IOException {
String serverCnxnFactoryName =
System.getProperty(ZOOKEEPER_SERVER_CNXN_FACTORY);
if (serverCnxnFactoryName == null) {
serverCnxnFactoryName = NIOServerCnxnFactory.class.getName();
}
try {
return (ServerCnxnFactory) Class.forName(serverCnxnFactoryName)
.newInstance();
} catch (Exception e) {
IOException ioe = new IOException("Couldn't instantiate "
+ serverCnxnFactoryName);
ioe.initCause(e);
throw ioe;
}
}
```
z之后初始化QuorumPeer，进行相应的配置,最后启动QuorumPeer
```
ServerCnxnFactory cnxnFactory = ServerCnxnFactory.createFactory();
cnxnFactory.configure(config.getClientPortAddress(),
config.getMaxClientCnxns());

quorumPeer = new QuorumPeer();
quorumPeer.setClientPortAddress(config.getClientPortAddress());
quorumPeer.setTxnFactory(new FileTxnSnapLog(
new File(config.getDataLogDir()),
new File(config.getDataDir())));
quorumPeer.setQuorumPeers(config.getServers());
quorumPeer.setElectionType(config.getElectionAlg());
quorumPeer.setMyid(config.getServerId());
quorumPeer.setTickTime(config.getTickTime());
quorumPeer.setMinSessionTimeout(config.getMinSessionTimeout());
quorumPeer.setMaxSessionTimeout(config.getMaxSessionTimeout());
quorumPeer.setInitLimit(config.getInitLimit());
quorumPeer.setSyncLimit(config.getSyncLimit());
quorumPeer.setQuorumVerifier(config.getQuorumVerifier());
quorumPeer.setCnxnFactory(cnxnFactory);
quorumPeer.setZKDatabase(new ZKDatabase(quorumPeer.getTxnFactory()));
quorumPeer.setLearnerType(config.getPeerType());
quorumPeer.setSyncEnabled(config.getSyncEnabled());
quorumPeer.setQuorumListenOnAllIPs(config.getQuorumListenOnAllIPs());

quorumPeer.start();
quorumPeer.join();
```
ServerCnxnFactory.configure()这里配置ServerSocketChannel
```
public void configure(InetSocketAddress addr, int maxcc) throws IOException {
configureSaslLogin();

thread = new Thread(this, "NIOServerCxn.Factory:" + addr);
thread.setDaemon(true);
maxClientCnxns = maxcc;
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);
}
```
QuorumPeer.start()
```
public synchronized void start() {
loadDataBase();
cnxnFactory.start();
startLeaderElection();
super.start();
}
```
1，首先加载数据 loadDataBase();

2，启动NIO线程；

3，启动leader选举

首先看从本地加载数据loadDataBase();
```
public long loadDataBase() throws IOException {
PlayBackListener listener=new PlayBackListener(){
public void onTxnLoaded(TxnHeader hdr,Record txn){
Request r = new Request(null, 0, hdr.getCxid(),hdr.getType(),
null, null);
r.txn = txn;
r.hdr = hdr;
r.zxid = hdr.getZxid();
addCommittedProposal(r);
}
};

long zxid = snapLog.restore(dataTree,sessionsWithTimeouts,listener);
initialized = true;
return zxid;
}

```
从zk的事务日志snapLog中恢复
```
long zxid = snapLog.restore(dataTree,sessionsWithTimeouts,listener);
```
之后会回调PlayBackListener的onTxnLoaded来onTxnLoaded提交Proposal(addCommittedProposal（）)
```
public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
snapLog.deserialize(dt, sessions);
FileTxnLog txnLog = new FileTxnLog(dataDir);
TxnIterator itr = txnLog.read(dt.lastProcessedZxid+1);
long highestZxid = dt.lastProcessedZxid;
TxnHeader hdr;
try {
while (true) {
// iterator points to
// the first valid txn when initialized
hdr = itr.getHeader();
if (hdr == null) {
//empty logs
return dt.lastProcessedZxid;
}
if (hdr.getZxid() < highestZxid && highestZxid != 0) {
LOG.error("{}(higestZxid) > {}(next log) for type {}",
new Object[] { highestZxid, hdr.getZxid(),
hdr.getType() });
} else {
highestZxid = hdr.getZxid();
}
try {
processTransaction(hdr,dt,sessions, itr.getTxn());
} catch(KeeperException.NoNodeException e) {
throw new IOException("Failed to process transaction type: " +
hdr.getType() + " error: " + e.getMessage(), e);
}
listener.onTxnLoaded(hdr, itr.getTxn());
if (!itr.next())
break;
}
} finally {
if (itr != null) {
itr.close();
}
}
return highestZxid;
}
```

启动NIOServerCnxnFactory的start()
```
public void start() {
// ensure thread is started once and only once
if (thread.getState() == Thread.State.NEW) {
thread.start();
}
}
```
这里的thread其实就是NIOServerCnxnFactory
```
thread = new Thread(this, "NIOServerCxn.Factory:" + addr);
thread.setDaemon(true);
```
然后来到run()循环
```
public void run() {
while (!ss.socket().isClosed()) {
try {
selector.select(1000);
Set<SelectionKey> selected;
synchronized (this) {
selected = selector.selectedKeys();
}
ArrayList<SelectionKey> selectedList = new ArrayList<SelectionKey>(
selected);
Collections.shuffle(selectedList);
for (SelectionKey k : selectedList) {
if ((k.readyOps() & SelectionKey.OP_ACCEPT) != 0) {
SocketChannel sc = ((ServerSocketChannel) k
.channel()).accept();
InetAddress ia = sc.socket().getInetAddress();
int cnxncount = getClientCnxnCount(ia);
if (maxClientCnxns > 0 && cnxncount >= maxClientCnxns){
LOG.warn("Too many connections from " + ia
+ " - max is " + maxClientCnxns );
sc.close();
} else {
LOG.info("Accepted socket connection from "
+ sc.socket().getRemoteSocketAddress());
sc.configureBlocking(false);
SelectionKey sk = sc.register(selector,
SelectionKey.OP_READ);
NIOServerCnxn cnxn = createConnection(sc, sk);
sk.attach(cnxn);
addCnxn(cnxn);
}
} else if ((k.readyOps() & (SelectionKey.OP_READ | SelectionKey.OP_WRITE)) != 0) {
NIOServerCnxn c = (NIOServerCnxn) k.attachment();
c.doIO(k);
} else {
if (LOG.isDebugEnabled()) {
LOG.debug("Unexpected ops in select "
+ k.readyOps());
}
}
}
selected.clear();
} catch (RuntimeException e) {
LOG.warn("Ignoring unexpected runtime exception", e);
} catch (Exception e) {
LOG.warn("Ignoring exception", e);
}
}
closeAll();
LOG.info("NIOServerCnxn factory exited run method");
}
```
监听IO，阻塞等待数据到来（1s）
```
selector.select(1000);
Set<SelectionKey> selected;
synchronized (this) {
selected = selector.selectedKeys();
}
ArrayList<SelectionKey> selectedList = new ArrayList<SelectionKey>(
selected);
Collections.shuffle(selectedList);
```
如果是连接，则accept，生成则在selector中注册SelectionKey.OP_READ事件 ，在没有达到maxClientCnxns时会创建一个连接createConnection,保存在set中
```
LOG.info("Accepted socket connection from "
+ sc.socket().getRemoteSocketAddress());
sc.configureBlocking(false);
SelectionKey sk = sc.register(selector,
SelectionKey.OP_READ);
NIOServerCnxn cnxn = createConnection(sc, sk);
sk.attach(cnxn);
addCnxn(cnxn);
```
处理OP_READ，OP_WRITE 读写时间
```
if ((k.readyOps() & (SelectionKey.OP_READ | SelectionKey.OP_WRITE)) != 0) {
NIOServerCnxn c = (NIOServerCnxn) k.attachment();
c.doIO(k);
}
```
```
/**
* Handles read/write IO on connection.
*/
void doIO(SelectionKey k) throws InterruptedException {
try {
if (isSocketOpen() == false) {
LOG.warn("trying to do i/o on a null socket for session:0x"
+ Long.toHexString(sessionId));

return;
}
if (k.isReadable()) {
int rc = sock.read(incomingBuffer);
if (rc < 0) {
throw new EndOfStreamException(
"Unable to read additional data from client sessionid 0x"
+ Long.toHexString(sessionId)
+ ", likely client has closed socket");
}
if (incomingBuffer.remaining() == 0) {
boolean isPayload;
if (incomingBuffer == lenBuffer) { // start of next request
incomingBuffer.flip();
isPayload = readLength(k);
incomingBuffer.clear();
} else {
// continuation
isPayload = true;
}
if (isPayload) { // not the case for 4letterword
readPayload();
}
else {
// four letter words take care
// need not do anything else
return;
}
}
}
if (k.isWritable()) {
// ZooLog.logTraceMessage(LOG,
// ZooLog.CLIENT_DATA_PACKET_TRACE_MASK
// "outgoingBuffers.size() = " +
// outgoingBuffers.size());
if (outgoingBuffers.size() > 0) {
// ZooLog.logTraceMessage(LOG,
// ZooLog.CLIENT_DATA_PACKET_TRACE_MASK,
// "sk " + k + " is valid: " +
// k.isValid());

/*
* This is going to reset the buffer position to 0 and the
* limit to the size of the buffer, so that we can fill it
* with data from the non-direct buffers that we need to
* send.
*/
ByteBuffer directBuffer = factory.directBuffer;
directBuffer.clear();

for (ByteBuffer b : outgoingBuffers) {
if (directBuffer.remaining() < b.remaining()) {
/*
* When we call put later, if the directBuffer is to
* small to hold everything, nothing will be copied,
* so we've got to slice the buffer if it's too big.
*/
b = (ByteBuffer) b.slice().limit(
directBuffer.remaining());
}
/*
* put() is going to modify the positions of both
* buffers, put we don't want to change the position of
* the source buffers (we'll do that after the send, if
* needed), so we save and reset the position after the
* copy
*/
int p = b.position();
directBuffer.put(b);
b.position(p);
if (directBuffer.remaining() == 0) {
break;
}
}
/*
* Do the flip: limit becomes position, position gets set to
* 0. This sets us up for the write.
*/
directBuffer.flip();

int sent = sock.write(directBuffer);
ByteBuffer bb;

// Remove the buffers that we have sent
while (outgoingBuffers.size() > 0) {
bb = outgoingBuffers.peek();
if (bb == ServerCnxnFactory.closeConn) {
throw new CloseRequestException("close requested");
}
int left = bb.remaining() - sent;
if (left > 0) {
/*
* We only partially sent this buffer, so we update
* the position and exit the loop.
*/
bb.position(bb.position() + sent);
break;
}
packetSent();
/* We've sent the whole buffer, so drop the buffer */
sent -= bb.remaining();
outgoingBuffers.remove();
}
// ZooLog.logTraceMessage(LOG,
// ZooLog.CLIENT_DATA_PACKET_TRACE_MASK, "after send,
// outgoingBuffers.size() = " + outgoingBuffers.size());
}

synchronized(this.factory){
if (outgoingBuffers.size() == 0) {
if (!initialized
&& (sk.interestOps() & SelectionKey.OP_READ) == 0) {
throw new CloseRequestException("responded to info probe");
}
sk.interestOps(sk.interestOps()
& (~SelectionKey.OP_WRITE));
} else {
sk.interestOps(sk.interestOps()
| SelectionKey.OP_WRITE);
}
}
}
} catch (CancelledKeyException e) {
LOG.warn("Exception causing close of session 0x"
+ Long.toHexString(sessionId)
+ " due to " + e);
if (LOG.isDebugEnabled()) {
LOG.debug("CancelledKeyException stack trace", e);
}
close();
} catch (CloseRequestException e) {
// expecting close to log session closure
close();
} catch (EndOfStreamException e) {
LOG.warn("caught end of stream exception",e); // tell user why

// expecting close to log session closure
close();
} catch (IOException e) {
LOG.warn("Exception causing close of session 0x"
+ Long.toHexString(sessionId)
+ " due to " + e);
if (LOG.isDebugEnabled()) {
LOG.debug("IOException stack trace", e);
}
close();
}
}
```