摘要
本节讲解ServerCnxn的NIO实现方式,也就是NIOServerCnxn（NettyServerCnxn就不讲了）
NIOServerCnxn继承了ServerCnxn抽象类，用NIO来处理与客户端之间的通信，单线程处理。
主要讲解
内部类
SendBufferWriter定义一些Writer的实现，来完成cmd处理时的一些输出
CommandThread完成不同cmd的处理
属性
函数
构造函数
IO相关
doIO核心函数
读相关
readLength读取四个字节，判断是否是payload这种请求
checkFourLetterWord看四个字节和cmd对应的是否匹配，是的话完成printWriter对应的写操作
readPayload读取len后面对应大小的buffer进行处理
readConnectRequest读取连接请求
readRequest读取非连接的请求
写相关
sendCloseSession发送close的buffer
sendBufferSync同步发送
sendBuffer普通发送
继承父类serverCnxn的函数
实现接口Watcher相关函数
相关介绍
client发送请求的类型
源码中，体现为两种
payload:翻译是"有效载荷"，代表的是前面四个字节的int代表len，后续有对应len长度的buffer
非payload:前面四个字节int，对应ServerCnxn中定义的不同cmd，如“conf”(对应int 1668247142)，“cons”(对应 1668247155)等，不同的cmd后续可能跟着不同的，特定长度的buffer
内部类
NIOServerCnxn内部类
SendBufferWriter
该类用来将给客户端的响应进行分块
避免response太大，没有写完而一直占用空间,因此对response分块
/**
* This class wraps the sendBuffer method of NIOServerCnxn. It is
* responsible for chunking up the response to a client. Rather
* than cons'ing up a response fully in memory, which may be large
* for some commands, this class chunks up the result.
*/
private class SendBufferWriter extends Writer {
private StringBuffer sb = new StringBuffer();
/**
* Check if we are ready to send another chunk.
* @param force force sending, even if not a full chunk
*/
private void checkFlush(boolean force) {
if ((force && sb.length() > 0) || sb.length() > 2048) {// 当强制发送并且sb大小大于0，或者sb大小大于2048即发送缓存
sendBufferSync(ByteBuffer.wrap(sb.toString().getBytes()));//sockChannel完成对应的发送
// clear our internal buffer
sb.setLength(0);
}
}
@Override
public void close() throws IOException {
if (sb == null) return;
checkFlush(true);// 关闭之前需要强制性发送缓存
sb = null; // clear out the ref to ensure no reuse
}
@Override
public void flush() throws IOException {
checkFlush(true);//强制发送
}
@Override
public void write(char[] cbuf, int off, int len) throws IOException {
sb.append(cbuf, off, len);//sb写入内容
checkFlush(false);//非强制发送
}
}
CommandThread
用于处理ServerCnxn中的定义的命令，如"ruok","stmk".其主要逻辑定义在commandRun方法中，在子类中各自实现，每个命令使用单独的线程进行处理。
/**
* Set of threads for commmand ports. All the 4
* letter commands are run via a thread. Each class
* maps to a corresponding 4 letter command. CommandThread
* is the abstract class from which all the others inherit.
*/
private abstract class CommandThread extends Thread {
PrintWriter pw;
CommandThread(PrintWriter pw) {
this.pw = pw;
}
public void run() {
try {
commandRun();
} catch (IOException ie) {
LOG.error("Error in running command ", ie);
} finally {
cleanupWriterSocket(pw);
}
}
public abstract void commandRun() throws IOException;
}
它有很多个子类，这里只列举一个DumpCommand,感受一下即可,实现commandRun，完成对应操作，写入PrintWriter就行。
private class DumpCommand extends CommandThread {
public DumpCommand(PrintWriter pw) {
super(pw);
}
@Override
public void commandRun() {
if (zkServer == null) {
pw.println(ZK_NOT_SERVING);
}
else {
pw.println("SessionTracker dump:");
zkServer.sessionTracker.dumpSessions(pw);
pw.println("ephemeral nodes dump:");
zkServer.dumpEphemerals(pw);
}
}
}
属性
static final Logger LOG = LoggerFactory.getLogger(NIOServerCnxn.class);
NIOServerCnxnFactory factory;// ServerCnxn工厂
final SocketChannel sock;// 针对面向流的连接套接字的可选择通道
private final SelectionKey sk;//对于ACCEPT，CONNECT，READ，WRITE感兴趣的key组合
boolean initialized;
ByteBuffer lenBuffer = ByteBuffer.allocate(4);// 分配四个字节缓冲区,用于读取len长度,空间大小绝对不会变
ByteBuffer incomingBuffer = lenBuffer;//读取输入流，会根据读取到的len再分配对应的长度
LinkedBlockingQueue<ByteBuffer> outgoingBuffers = new LinkedBlockingQueue<ByteBuffer>();//输入的缓冲队列
int sessionTimeout;//会话超时时间
private final ZooKeeperServer zkServer;//zkServer服务器
/**
* The number of requests that have been submitted but not yet responded to.
*/
int outstandingRequests;//已提交但是尚未回复的请求数
/**
* This is the id that uniquely identifies the session of a client. Once
* this session is no longer active, the ephemeral nodes will go away.
*/
long sessionId;// 会话ID
static long nextSessionId = 1;// 下个会话ID
int outstandingLimit = 1;//默认的，能够容忍的 已提交但是尚未回复的请求数，后面会重新赋值
private static final String ZK_NOT_SERVING =
"This ZooKeeper instance is not currently serving requests";
private final static byte fourBytes[] = new byte[4];
函数
构造函数
public NIOServerCnxn(ZooKeeperServer zk, SocketChannel sock,
SelectionKey sk, NIOServerCnxnFactory factory) throws IOException {
this.zkServer = zk;//zk服务器
this.sock = sock;
this.sk = sk;//对应的感兴趣的key
this.factory = factory;//工厂方法
if (this.factory.login != null) {
this.zooKeeperSaslServer = new ZooKeeperSaslServer(factory.login);
}
if (zk != null) {
outstandingLimit = zk.getGlobalOutstandingLimit();//获取能够容忍的 接收到但是还没有回复的请求的数量
}
sock.socket().setTcpNoDelay(true);
/* set socket linger to false, so that socket close does not
* block */
sock.socket().setSoLinger(false, -1);
InetAddress addr = ((InetSocketAddress) sock.socket()
.getRemoteSocketAddress()).getAddress();
authInfo.add(new Id("ip", addr.getHostAddress()));
sk.interestOps(SelectionKey.OP_READ);//初始对READ感兴趣(之前已经连接上了，即处理过ACCEPT了)
}
对Socket通道进行相应设置，如设置TCP连接无延迟、获取客户端的IP地址并将此信息进行记录
最后设置SelectionKey感兴趣的操作类型为READ,准备读取后续消息
发送buffer相关
IO相关
核心函数 doIO
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);//读取len，判断是否是payload
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()) {//如果可写
// ZooLog.logTraceMessage(LOG,
// ZooLog.CLIENT_DATA_PACKET_TRACE_MASK
// "outgoingBuffers.size() = " +
// outgoingBuffers.size());
if (outgoingBuffers.size() > 0) {//发送队列不为空
// 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()) {//如果分配空间剩余不够，就进行分片
/*
* 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) {//写满一个buffer
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);//写入socket
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) {//如果还有内容没有发送
/*
* We only partially sent this buffer, so we update
* the position and exit the loop.
*/
bb.position(bb.position() + sent);
break;
}
packetSent();//更新统计数据
/* 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();
}
}
主要逻辑就是
1.可读，那么根据最开始4个字节的int，判断是否是payload
如果不是的话，代表是cmd，调用对应的处理函数写进printWriter
如果是的话，分配对应len的空间给buffer，读取后续请求内容
2.如果可写
那么遍历outgoingBuffers,然后每次写满一个64k的buffer空间（可能有分片的操作），然后进行发送
读取相关
在上面doIO中，调用到了如下函数
readLength
//读取前4个字节代表int，如果还没有初始化，并且int值是特定cmd对应的int，那么就当成是cmd，否则给incomingBuffer分配对应len的空间
private boolean readLength(SelectionKey k) throws IOException {
// Read the length, now get the buffer
int len = lenBuffer.getInt();
if (!initialized && checkFourLetterWord(sk, len)) {//如果没有初始化，并且是cmd的话，就写对应的printWriter回复
return false;
}
if (len < 0 || len > BinaryInputArchive.maxBuffer) {
throw new IOException("Len error " + len);
}
if (zkServer == null) {
throw new IOException("ZooKeeperServer not running");
}
incomingBuffer = ByteBuffer.allocate(len);//分配对应len的空间
return true;
}
checkFourLetterWord
验证int值是否对应特定的cmd，是的话写入对应回复到PrintWriter
private boolean checkFourLetterWord(final SelectionKey k, final int len)
throws IOException
{
// We take advantage of the limited size of the length to look
// for cmds. They are all 4-bytes which fits inside of an int
String cmd = cmd2String.get(len);
if (cmd == null) {
return false;
}
LOG.info("Processing " + cmd + " command from "
+ sock.socket().getRemoteSocketAddress());
packetReceived();
/** cancel the selection key to remove the socket handling
* from selector. This is to prevent netcat problem wherein
* netcat immediately closes the sending side after sending the
* commands and still keeps the receiving channel open.
* The idea is to remove the selectionkey from the selector
* so that the selector does not notice the closed read on the
* socket channel and keep the socket alive to write the data to
* and makes sure to close the socket after its done writing the data
*/
if (k != null) {
try {
k.cancel();
} catch(Exception e) {
LOG.error("Error cancelling command selection key ", e);
}
}
final PrintWriter pwriter = new PrintWriter(
new BufferedWriter(new SendBufferWriter()));
if (len == ruokCmd) {
RuokCommand ruok = new RuokCommand(pwriter);
ruok.start();
return true;
} else if (len == getTraceMaskCmd) {
TraceMaskCommand tmask = new TraceMaskCommand(pwriter);
tmask.start();
return true;
} else if (len == setTraceMaskCmd) {
incomingBuffer = ByteBuffer.allocate(8);
int rc = sock.read(incomingBuffer);
if (rc < 0) {
throw new IOException("Read error");
}
incomingBuffer.flip();
long traceMask = incomingBuffer.getLong();
ZooTrace.setTextTraceLevel(traceMask);
SetTraceMaskCommand setMask = new SetTraceMaskCommand(pwriter, traceMask);
setMask.start();
return true;
} else if (len == enviCmd) {
EnvCommand env = new EnvCommand(pwriter);
env.start();
return true;
} else if (len == confCmd) {
ConfCommand ccmd = new ConfCommand(pwriter);
ccmd.start();
return true;
} else if (len == srstCmd) {
StatResetCommand strst = new StatResetCommand(pwriter);
strst.start();
return true;
} else if (len == crstCmd) {
CnxnStatResetCommand crst = new CnxnStatResetCommand(pwriter);
crst.start();
return true;
} else if (len == dumpCmd) {
DumpCommand dump = new DumpCommand(pwriter);
dump.start();
return true;
} else if (len == statCmd || len == srvrCmd) {
StatCommand stat = new StatCommand(pwriter, len);
stat.start();
return true;
} else if (len == consCmd) {
ConsCommand cons = new ConsCommand(pwriter);
cons.start();
return true;
} else if (len == wchpCmd || len == wchcCmd || len == wchsCmd) {
WatchCommand wcmd = new WatchCommand(pwriter, len);
wcmd.start();
return true;
} else if (len == mntrCmd) {
MonitorCommand mntr = new MonitorCommand(pwriter);
mntr.start();
return true;
} else if (len == isroCmd) {
IsroCommand isro = new IsroCommand(pwriter);
isro.start();
return true;
}
return false;
}
readPayload
读取payload请求，即非cmd的请求
private void readPayload() throws IOException, InterruptedException {//读取payload的请求
if (incomingBuffer.remaining() != 0) { // have we read length bytes?
int rc = sock.read(incomingBuffer); // sock is non-blocking, so ok
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) { // have we read length bytes?
packetReceived();//更新统计数据
incomingBuffer.flip();
if (!initialized) {
readConnectRequest();//读取连接请求
} else {
readRequest();//读取请求
}
lenBuffer.clear();
incomingBuffer = lenBuffer;//还原成只读4个字节的byte
}
}
readConnectRequest
读取连接请求,调用ZooKeeperServer相关逻辑
private void readConnectRequest() throws IOException, InterruptedException {
if (zkServer == null) {
throw new IOException("ZooKeeperServer not running");
}
zkServer.processConnectRequest(this, incomingBuffer);
initialized = true;//标记初始化完成
}
readRequest
读取非连接的请求
private void readRequest() throws IOException {
zkServer.processPacket(this, incomingBuffer);
}
发送相关
doIO里面并没有直接利用发送相关的函数
sendCloseSession
发送"关闭"的buffer
/**
* send buffer without using the asynchronous
* calls to selector and then close the socket
* @param bb
*/
public void sendCloseSession() {
sendBuffer(ServerCnxnFactory.closeConn);
}
sendBufferSync
同步发送
/**
* send buffer without using the asynchronous
* calls to selector and then close the socket
* @param bb
*/
void sendBufferSync(ByteBuffer bb) {//同步发送
try {
/* configure socket to be blocking
* so that we dont have to do write in
* a tight while loop
*/
sock.configureBlocking(true);
if (bb != ServerCnxnFactory.closeConn) {
if (sock.isOpen()) {
sock.write(bb);
}
packetSent();
}
} catch (IOException ie) {
LOG.error("Error sending data synchronously ", ie);
}
}
sendBuffer
发送的核心函数
public void sendBuffer(ByteBuffer bb) {//发送
try {
if (bb != ServerCnxnFactory.closeConn) {//如果不是"关闭"的回复
// We check if write interest here because if it is NOT set,
// nothing is queued, so we can try to send the buffer right
// away without waking up the selector
if ((sk.interestOps() & SelectionKey.OP_WRITE) == 0) {//如果目前selectionKey还未注册WRITE(代表不能用NIO的方式)，则直接写
try {
sock.write(bb);
} catch (IOException e) {
// we are just doing best effort right now
}
}
// if there is nothing left to send, we are done
if (bb.remaining() == 0) {//如果读取完内容，则更新发包次数
packetSent();
return;
}
}
synchronized(this.factory){
sk.selector().wakeup();
if (LOG.isTraceEnabled()) {
LOG.trace("Add a buffer to outgoingBuffers, sk " + sk
+ " is valid: " + sk.isValid());
}
outgoingBuffers.add(bb);//添加到发送缓存队列
if (sk.isValid()) {
sk.interestOps(sk.interestOps() | SelectionKey.OP_WRITE);//注册WRITE事件
}
}
} catch(Exception e) {
LOG.error("Unexpected Exception: ", e);
}
}
主要逻辑如下
如果不是"关闭"的ByteBuffer，如果能用NIO的方式就用NIO的方式，加入outgoingBuffers队列，否则就直接同步发送了
继承父类ServerCnxn的方法
有很多，这里只用列举一个即可
incrOutstandingRequests
//增加尚未处理的请求个数
protected void incrOutstandingRequests(RequestHeader h) {
if (h.getXid() >= 0) {
synchronized (this) {
outstandingRequests++;
}
synchronized (this.factory) {
// check throttling
if (zkServer.getInProcess() > outstandingLimit) {//如果超过阈值了，就禁止读
if (LOG.isDebugEnabled()) {
LOG.debug("Throttling recv " + zkServer.getInProcess());
}
disableRecv();
// following lines should not be needed since we are
// already reading
// } else {
// enableRecv();
}
}
}
}
实现接口Watcher相关
实现接口方法process
synchronized public void process(WatchedEvent event) {
ReplyHeader h = new ReplyHeader(-1, -1L, 0);//xid为-1表示为通知
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG, ZooTrace.EVENT_DELIVERY_TRACE_MASK,
"Deliver event " + event + " to 0x"
+ Long.toHexString(this.sessionId)
+ " through " + this);
}
// Convert WatchedEvent to a type that can be sent over the wire
WatcherEvent e = event.getWrapper();//包装为WatcherEvent来提供网络传输
sendResponse(h, e, "notification");//给client发送请求,通知WatchedEvent的发生
}
里面调用了函数sendResponse,主要是进行一些序列化的操作，然后把对应长度len写入，方便client读,完成一些数据统计，更新的操作
synchronized public void sendResponse(ReplyHeader h, Record r, String tag) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
// Make space for length
BinaryOutputArchive bos = BinaryOutputArchive.getArchive(baos);
try {
baos.write(fourBytes);
bos.writeRecord(h, "header");
if (r != null) {
bos.writeRecord(r, tag);
}
baos.close();
} catch (IOException e) {
LOG.error("Error serializing response");
}
byte b[] = baos.toByteArray();
ByteBuffer bb = ByteBuffer.wrap(b);
bb.putInt(b.length - 4).rewind();//把len-4放入byteBuffer，代表后续内容的长度
sendBuffer(bb);
if (h.getXid() > 0) {
synchronized(this){
outstandingRequests--;
}
// check throttling
synchronized (this.factory) {
if (zkServer.getInProcess() < outstandingLimit
|| outstandingRequests < 1) {
sk.selector().wakeup();
enableRecv();//开启写
}
}
}
} catch(Exception e) {
LOG.warn("Unexpected exception. Destruction averted.", e);
}
}
里面调用的sendBuffer在上面已经讲过了
cmd处理相关
cleanupWriterSocket函数完成对应cmd处理器写完printWriter之后进行关闭
private void cleanupWriterSocket(PrintWriter pwriter) {
try {
if (pwriter != null) {
pwriter.flush();
pwriter.close();
}
} catch (Exception e) {
LOG.info("Error closing PrintWriter ", e);
} finally {
try {
close();
} catch (Exception e) {
LOG.error("Error closing a command socket ", e);
}
}
}
思考
server在response最开始4个字节写入了len，client是如何处理的
在前面阅读源码18中讲过，ClientCnxnSocketNIO#doIO,逻辑如下
client先读取长度，再分配对应空间，读取后续response
NIOServerCnxn构造函数中，感兴趣的事件就是READ，那么ACCEPT是在哪完成的
因为先要完成server 接受 client的连接，那么这一步在哪完成,这里简要带过后面才讲的
NIOServerCnxnFactory
server对ACCEPT事件的注册,NIOServerCnxnFactory#configure
server接受client连接,在读取client的请求，如下
NIOServerCnxnFactory#run
server接受连接，读取请求
doIO函数是哪里调用的
是NIOServerCnxnFactory#run中根据SelectionKey的attachment获取NIOServerCnxn对象，读写就绪时调用的,对应源码NIOServerCnxnFactory#run，这里不展开
doIO的调用方
吐槽
client发送请求的类型判断bug
在上面介绍payload和非payload过程中，其实都是根据开头4个字节得到int，而判断是不是非payload就根据mapping规则来，比如如果int值是"conf"对应的1668247142,那么就认为是conf的cmd，而不会认为是有1668247142这么大的byteBuffer。感觉是一个bug。如果刚好长度这么大，就会被认为成conf的cmd了。
nio相关的东西太多了
这个也没办法，这就是nio的实现
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