org.apache.zookeeper.server.quorum

Class Learner

java.lang.Object

org.apache.zookeeper.server.quorum.Learner

Direct Known Subclasses:

Follower, Observer

public class Learner
extends Object

This class is the superclass of two of the three main actors in a ZK ensemble: Followers and Observers. Both Followers and Observers share a good deal of code which is moved into Peer to avoid duplication.

Field Summary

Fields

Modifier and Type	Field and Description
protected BufferedOutputStream	bufferedOutput
protected MultipleAddresses	leaderAddr
protected InputArchive	leaderIs
protected OutputArchive	leaderOs
protected int	leaderProtocolVersion the protocol version of the leader
protected static org.slf4j.Logger	LOG
protected MessageTracker	messageTracker
protected Socket	sock

Constructor Summary

Constructors

Constructor and Description
Learner()

Method Summary

Modifier and Type	Method and Description
protected void	connectToLeader(MultipleAddresses multiAddr, String hostname) Establish a connection with the LearnerMaster found by findLearnerMaster.
protected Socket	createSocket() Creating a simple or and SSL socket.
protected QuorumPeer.QuorumServer	findLeader() Returns the address of the node we think is the leader.
int	getPendingRevalidationsCount()
Socket	getSocket() Socket getter
protected long	nanoTime() Overridable helper method to return the System.nanoTime().
protected void	ping(QuorumPacket qp)
protected long	registerWithLeader(int pktType) Once connected to the leader or learner master, perform the handshake protocol to establish a following / observing connection.
protected void	revalidate(QuorumPacket qp)
void	shutdown() Shutdown the Peer
protected void	sockConnect(Socket sock, InetSocketAddress addr, int timeout) Overridable helper method to simply call sock.connect().
protected void	syncWithLeader(long newLeaderZxid) Finally, synchronize our history with the Leader (if Follower) or the LearnerMaster (if Observer).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

bufferedOutput

protected BufferedOutputStream bufferedOutput

sock

protected Socket sock

leaderAddr

protected MultipleAddresses leaderAddr

leaderIs

protected InputArchive leaderIs

leaderOs

protected OutputArchive leaderOs

leaderProtocolVersion

protected int leaderProtocolVersion

the protocol version of the leader

messageTracker

protected final MessageTracker messageTracker

LOG

protected static final org.slf4j.Logger LOG

Constructor Detail

Learner

public Learner()

Method Detail

getSocket

public Socket getSocket()

Socket getter

Returns:

getPendingRevalidationsCount

public int getPendingRevalidationsCount()

findLeader

protected QuorumPeer.QuorumServer findLeader()

Returns the address of the node we think is the leader.

nanoTime

protected long nanoTime()

Overridable helper method to return the System.nanoTime(). This method behaves identical to System.nanoTime().

sockConnect

protected void sockConnect(Socket sock,
                           InetSocketAddress addr,
                           int timeout)
                    throws IOException

Overridable helper method to simply call sock.connect(). This can be overriden in tests to fake connection success/failure for connectToLeader.

Throws:

IOException

connectToLeader

protected void connectToLeader(MultipleAddresses multiAddr,
                               String hostname)
                        throws IOException

Establish a connection with the LearnerMaster found by findLearnerMaster. Followers only connect to Leaders, Observers can connect to any active LearnerMaster. Retries until either initLimit time has elapsed or 5 tries have happened.

Parameters:

multiAddr - - the address of the Peer to connect to.

Throws:

IOException - - if the socket connection fails on the 5th attempt if there is an authentication failure while connecting to leader

createSocket

protected Socket createSocket()
                       throws X509Exception,
                              IOException

Creating a simple or and SSL socket. This can be overridden in tests to fake already connected sockets for connectToLeader.

Throws:

X509Exception

IOException

registerWithLeader

protected long registerWithLeader(int pktType)
                           throws IOException

Once connected to the leader or learner master, perform the handshake protocol to establish a following / observing connection.

Parameters:

pktType -

Returns:

the zxid the Leader sends for synchronization purposes.

Throws:

IOException

syncWithLeader

protected void syncWithLeader(long newLeaderZxid)
                       throws Exception

Finally, synchronize our history with the Leader (if Follower) or the LearnerMaster (if Observer).

Parameters:

newLeaderZxid -

Throws:

IOException

InterruptedException

Exception

revalidate

protected void revalidate(QuorumPacket qp)
                   throws IOException

Throws:

IOException

ping

protected void ping(QuorumPacket qp)
             throws IOException

Throws:

IOException

shutdown

public void shutdown()

Shutdown the Peer