ZooKeeper源码阅读（二）：客户端
源代码：
http://svn.apache.org/repos/asf/zookeeper/trunk/
导入eclipse：
在包含build.xml目录下执行ant eclipse将产生.classpath文件
目录结构：
src/recipes：提供了各种Zookeeper应用例子
src/c：提供了c版客户端。zookeeper_st,zookeeper_mt两个library
src/contrib：别人贡献的代码?
src/generated：由jute生成的java实体类
客户端入口：org.apache.zookeeper.ZooKeeperMain
//读取命令行输入，用MyCommandOptions解析。
//内部类MyCommandOptions包含成员命令名command、参数列表cmdArgs
-option value –option value command cmdArgs
//根据以上解析的ip、端口，连接到ZooKeeper
zk = newZooKeeper(host,
Integer.parseInt(cl.getOption("timeout")),
newMyWatcher(), readOnly);
//执行命令，在ZooKeeperMain.run()
//ZooKeeperMain只是一个外壳，使用jline实现了命令提示功能。
//commandMapCli将提供的命令命令名与执行体CliCommand关联
//execute from commandMap
CliCommandcliCmd = commandMapCli.get(cmd);
if(cliCmd!=null) {
cliCmd.setZk(zk);
watch =cliCmd.parse(args).exec();
}
//最终转到调用ZooKeeper方法
//提供的命令：
quit：Zk.close()关闭zk连接，调用cnxn.close()
history：列出历史记录
redo index：重新执行历史记录
printwatches [on]：查看/设置watche开关状态
connect：connectToZK(host)连接zk
//ZooKeeper内部连接
cnxn = newClientCnxn(connectStringParser.getChrootPath(),
hostProvider,sessionTimeout,this,watchManager,
getClientCnxnSocket(),canBeReadOnly);
cnxn.start();
ClientCnxn包含SendThread和EventThread两个线程
SendThread将事件添加到waitEvents队列中，EventThread线程消费该队列。
//下面以ls命令为例
//调用zk.getChildren
public boolean exec() throwsKeeperException, InterruptedException {
String path= args[1];
boolean watch =cl.hasOption("w");
List<String> children = zk.getChildren(path, watch);
out.println(children);
return watch;
}
//getChildren生成request
RequestHeader h = newRequestHeader();
h.setType(ZooDefs.OpCode.getChildren);
GetChildrenRequest request = newGetChildrenRequest();
request.setPath(serverPath);
request.setWatch(watcher != null);
GetChildrenResponse response = newGetChildrenResponse();
ReplyHeader r = cnxn.submitRequest(h, request,response, wcb);
//submitRequest调用queuePacket
publicReplyHeadersubmitRequest(RequestHeaderh, Record request,
Recordresponse, WatchRegistration watchRegistration)
throwsInterruptedException {
ReplyHeaderr = new ReplyHeader();
Packetpacket = queuePacket(h,r, request, response,null,null,null,
null, watchRegistration);
synchronized(packet) {
while (!packet.finished) {
packet.wait();
}
}
return r;
}
//queuePacket将Packet添加到outgoingQueue队列中
packet= new Packet(h, r, request, response,watchRegistration);
packet.cb = cb;
packet.ctx = ctx;
packet.clientPath =clientPath;
packet.serverPath =serverPath;
outgoingQueue.add(packet);
//然后唤醒selector
sendThread.getClientCnxnSocket().wakeupCnxn();
//sendThread.run消费outgoingQueue
clientCnxnSocket.doTransport(to,pendingQueue,outgoingQueue,ClientCnxn.this);
//selector判断读/写事件
//doTransport调用doIO，doIO解析Response
//读事件
int rc =sock.read(incomingBuffer);
sendThread.readResponse(incomingBuffer);
//写事件
sock.write(p.bb);
//readResponse在finally块中调用finishPacket，finishPacket将设置packet.finish，
//此时submitRequest返回response。
try {
packet.replyHeader.setXid(replyHdr.getXid());
packet.replyHeader.setErr(replyHdr.getErr());
packet.replyHeader.setZxid(replyHdr.getZxid());
if(replyHdr.getZxid() > 0) {
lastZxid =replyHdr.getZxid();
}
if(packet.response !=null&& replyHdr.getErr() == 0) {
packet.response.deserialize(bbia,"response");
}
} finally {
finishPacket(packet);
}
