zookeeper源码分析-client分析

最近在阅读 zookeeper的源码。此系列文章仅作为个人记录，所以可能有点乱
zookeeper client端的代码分析:

zookeeper client 与 server之间的所有通信，包括 ping, getData, getChild, event 等等，都是通过ClientCnxnSocket 的实现类ClientCnxnSocketNIO 去做的。 ClientCnxnSocketNIO的源码如下：

public class ClientCnxnSocketNIO extends ClientCnxnSocket {
    private static final Logger LOG = LoggerFactory
            .getLogger(ClientCnxnSocketNIO.class);

    private final Selector selector = Selector.open();

    private SelectionKey sockKey;

    ClientCnxnSocketNIO() throws IOException {
        super();
    }

Client 是由两个线程处理所有的事情的。SendThread处理所有请求的发送和相应的接受，该线程只关心两个队列，outgoingQueue和pendingQueue。要被发送的请求都会被ClientCnxn以packet的形式放入到 outgoingQueue中，对于用户的请求（不是ping和权限验证的请求）再发送出去后会被SendThread放入到pendingQueue中。当SendThread 接受到response（包括events 和其他的请求结果）时，会通过eventThread放入到WaitingEvents队列中，等待eventThread处理。

ClientCnxn 部分源码如下：

public class ClientCnxn {
    private static final Logger LOG = LoggerFactory.getLogger(ClientCnxn.class);

    private static final String ZK_SASL_CLIENT_USERNAME =
        "zookeeper.sasl.client.username";

    /** This controls whether automatic watch resetting is enabled.
     * Clients automatically reset watches during session reconnect, this
     * option allows the client to turn off this behavior by setting
     * the environment variable "zookeeper.disableAutoWatchReset" to "true" */
    private static boolean disableAutoWatchReset;
    static {
        // this var should not be public, but otw there is no easy way
        // to test
        disableAutoWatchReset =
            Boolean.getBoolean("zookeeper.disableAutoWatchReset");
        if (LOG.isDebugEnabled()) {
            LOG.debug("zookeeper.disableAutoWatchReset is "
                    + disableAutoWatchReset);
        }
    }

    static class AuthData {
        AuthData(String scheme, byte data[]) {
            this.scheme = scheme;
            this.data = data;
        }

        String scheme;

        byte data[];
    }

    private final CopyOnWriteArraySet<AuthData> authInfo = new CopyOnWriteArraySet<AuthData>();

    /**
     * These are the packets that have been sent and are waiting for a response.
     */
    private final LinkedList<Packet> pendingQueue = new LinkedList<Packet>();

    /**
     * These are the packets that need to be sent.
     */
    private final LinkedList<Packet> outgoingQueue = new LinkedList<Packet>();

    private int connectTimeout;

    /**
     * The timeout in ms the client negotiated with the server. This is the
     * "real" timeout, not the timeout request by the client (which may have
     * been increased/decreased by the server which applies bounds to this
     * value.
     */
    private volatile int negotiatedSessionTimeout;

    private int readTimeout;

    private final int sessionTimeout;

    private final ZooKeeper zooKeeper;

    private final ClientWatchManager watcher;

EventThread部分源码如下：

    class EventThread extends Thread {
        private final LinkedBlockingQueue<Object> waitingEvents =
            new LinkedBlockingQueue<Object>();

        /** This is really the queued session state until the event
         * thread actually processes the event and hands it to the watcher.
         * But for all intents and purposes this is the state.
         */
        private volatile KeeperState sessionState = KeeperState.Disconnected;

       private volatile boolean wasKilled = false;
       private volatile boolean isRunning = false;