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);

}

以下图片转自：http://www.spnguru.com/2010/08/zookeeper%E5%85%A8%E8%A7%A3%E6%9E%90%E2%80%94%E2%80%94client%E7%AB%AF/