Package org.apache.derby.impl.store.replication.net

Class ReplicationMessageReceive

java.lang.Object

org.apache.derby.impl.store.replication.net.ReplicationMessageReceive

public class ReplicationMessageReceive
extends java.lang.Object

This class is the Receiver (viz. Socket server or listener) part of the network communication. It receives the message from the master and performs appropriate action depending on the type of the message.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
private class	ReplicationMessageReceive.SlavePingThread	Thread that sends ping messages to the master on request to check if the replication network is working

Field Summary

Fields

Modifier and Type	Field	Description
private boolean	connectionConfirmed	Whether or not the connection with the master is confirmed to be working.
private static int	DEFAULT_PING_TIMEOUT	The maximum number of millis to wait before giving up waiting for a ping response
private boolean	doSendPing	Whether or not the ping thread has been notified to check connection.
private boolean	killPingThread	Used to terminate the ping thread.
private java.lang.Thread	pingThread	Thread used to send ping messages to master to check if the connection is working.
private java.lang.Object	receivePongSemaphore	Used for synchronization when waiting for a ping reply message
private java.lang.Object	sendPingSemaphore	Used for synchronization of the ping thread
private java.net.ServerSocket	serverSocket	Contains the ServerSocket used to listen for connections from the replication master.
private SlaveAddress	slaveAddress	Contains the address (hostname and port number) of the slave to replicate to.
private SocketConnection	socketConn	Contains the methods used to read and write to the Object streams obtained from a Socket connection.

Constructor Summary

Constructors

Constructor	Description
ReplicationMessageReceive(SlaveAddress slaveAddress, java.lang.String dbname)	Constructor initializes the slave address used in replication.

Method Summary

Modifier and Type	Method	Description
private void	checkSocketConnection()	Verifies if the SocketConnection is valid.
private java.net.ServerSocket	createServerSocket()	Used to create a ServerSocket for listening to connections from the master.
private void	handleUnexpectedMessage(java.lang.String dbname, java.lang.String expextedMsgId, java.lang.String receivedMsgId)	Notify other replication peer that the message type was unexpected and throw a StandardException
void	initConnection(int timeout, long synchOnInstant, java.lang.String dbname)	Used to create the server socket, listen on the socket for connections from the master and verify compatibility with the database version of the master.
boolean	isConnectedToMaster()	Check if the repliation network is working.
private void	parseAndAckInstant(ReplicationMessage initiatorMessage, long synchOnInstant, java.lang.String dbname)	Used to parse the log instant initiator message from the master and check that the master and slave log files are in synch.
private void	parseAndAckVersion(ReplicationMessage initiatorMessage, java.lang.String dbname)	Used to parse the initiator message from the master and check if the slave is compatible with the master by comparing the UID of the ReplicationMessage class of the master, that is wrapped in the initiator message, with the UID of the same class in the slave.
ReplicationMessage	readMessage()	Used to read a replication message sent by the master.
void	sendMessage(ReplicationMessage message)	Used to send a replication message to the master.
void	tearDown()	Used to close the ServerSocket and the resources associated with it.

Methods inherited from class java.lang.Object

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

Field Detail

slaveAddress

private final SlaveAddress slaveAddress

Contains the address (hostname and port number) of the slave to replicate to.

serverSocket

private java.net.ServerSocket serverSocket

Contains the ServerSocket used to listen for connections from the replication master.

socketConn

private SocketConnection socketConn

Contains the methods used to read and write to the Object streams obtained from a Socket connection.

DEFAULT_PING_TIMEOUT

private static final int DEFAULT_PING_TIMEOUT

The maximum number of millis to wait before giving up waiting for a ping response

See Also:

Constant Field Values

pingThread

private java.lang.Thread pingThread

Thread used to send ping messages to master to check if the connection is working. The ping message must be sent from a separate thread because failed message shipping over TCP does not timeout for two minutes (not configurable).

killPingThread

private boolean killPingThread

Used to terminate the ping thread.

connectionConfirmed

private boolean connectionConfirmed

Whether or not the connection with the master is confirmed to be working. Set to false by isConnectedToMaster, set to true when a pong (i.e., a response to a ping) is received. Field protected by receivePongSemephore

sendPingSemaphore

private final java.lang.Object sendPingSemaphore

Used for synchronization of the ping thread

doSendPing

private boolean doSendPing

Whether or not the ping thread has been notified to check connection. Protected by sendPingSemaphore.

receivePongSemaphore

private final java.lang.Object receivePongSemaphore

Used for synchronization when waiting for a ping reply message

Constructor Detail

ReplicationMessageReceive

public ReplicationMessageReceive(SlaveAddress slaveAddress,
                                 java.lang.String dbname)

Constructor initializes the slave address used in replication. Accepts the host name and port number that constitute the slave address as parameters.

Parameters:

slaveAddress - the address (host name and port number) of the slave to connect to.

dbname - the name of the database.

Method Detail

initConnection

public void initConnection(int timeout,
                           long synchOnInstant,
                           java.lang.String dbname)
                    throws java.io.IOException,
                           StandardException,
                           java.lang.ClassNotFoundException

Used to create the server socket, listen on the socket for connections from the master and verify compatibility with the database version of the master.

Parameters:

timeout - The amount of time, in milliseconds, this method will wait for a connection to be established. If no connection has been established before the timeout, a IOException is raised with cause java.net.SocketTimeoutException

synchOnInstant - the slave log instant, used to check that the master and slave log files are in synch. If no chunks of log records have been received from the master yet, this is the end position in the current log file. If a chunk of log has been received, this is the instant of the log record received last. Note that there is a difference!

dbname - the name of the replicated database

Throws:

java.io.IOException - if an exception occurs while trying to create the SocketConnection class or while trying to open a connection.

java.lang.ClassNotFoundException - Class of a serialized object cannot be found.

StandardException - if an incompatible database version is found.

createServerSocket

private java.net.ServerSocket createServerSocket()
                                          throws java.io.IOException

Used to create a ServerSocket for listening to connections from the master.

Returns:

an instance of the ServerSocket class.

Throws:

java.io.IOException - if an exception occurs while trying to open a connection.

tearDown

public void tearDown()
              throws java.io.IOException

Used to close the ServerSocket and the resources associated with it.

Throws:

java.io.IOException - If an exception occurs while trying to close the socket or the associated resources.

parseAndAckVersion

private void parseAndAckVersion(ReplicationMessage initiatorMessage,
                                java.lang.String dbname)
                         throws java.io.IOException,
                                StandardException

Used to parse the initiator message from the master and check if the slave is compatible with the master by comparing the UID of the ReplicationMessage class of the master, that is wrapped in the initiator message, with the UID of the same class in the slave.

Parameters:

initiatorMessage - the object containing the UID.

dbname - the name of the replicated database

Throws:

java.io.IOException - If an exception occurs while sending the acknowledgment.

StandardException - If the UID's do not match.

parseAndAckInstant

private void parseAndAckInstant(ReplicationMessage initiatorMessage,
                                long synchOnInstant,
                                java.lang.String dbname)
                         throws java.io.IOException,
                                StandardException

Used to parse the log instant initiator message from the master and check that the master and slave log files are in synch.

Parameters:

initiatorMessage - the object containing the UID.

synchOnInstant - the slave log instant, used to check that the master and slave log files are in synch. If no chunks of log records have been received from the master yet, this is the end position in the current log file. If a chunk of log has been received, this is the instant of the log record received last. Note that there is a difference!

dbname - the name of the replicated database

Throws:

java.io.IOException - If an exception occurs while sending the acknowledgment.

StandardException - If the log files are not in synch

handleUnexpectedMessage

private void handleUnexpectedMessage(java.lang.String dbname,
                                     java.lang.String expextedMsgId,
                                     java.lang.String receivedMsgId)
                              throws StandardException,
                                     java.io.IOException

Notify other replication peer that the message type was unexpected and throw a StandardException

Parameters:

dbname - the name of the replicated database

expextedMsgId - the expected message type

receivedMsgId - the received message type

Throws:

StandardException - exception describing that an unexpected message was received is always thrown

java.io.IOException - thrown if an exception occurs while sending the error message

sendMessage

public void sendMessage(ReplicationMessage message)
                 throws java.io.IOException

Used to send a replication message to the master.

Parameters:

message - a ReplicationMessage object that contains the message to be transmitted.

Throws:

java.io.IOException - 1) if an exception occurs while transmitting the message, 2) if the connection handle is invalid.

readMessage

public ReplicationMessage readMessage()
                               throws java.lang.ClassNotFoundException,
                                      java.io.IOException

Used to read a replication message sent by the master. This method would wait on the connection from the master until a message is received or a connection failure occurs. Replication network layer specific messages (i.e. ping/pong messages) are handled internally and are not returned.

Returns:

a ReplicationMessage object that contains the reply that is sent.

Throws:

java.lang.ClassNotFoundException - Class of a serialized object cannot be found.

java.io.IOException - 1) if an exception occurs while reading from the stream, 2) if the connection handle is invalid.

checkSocketConnection

private void checkSocketConnection()
                            throws java.io.IOException

Verifies if the SocketConnection is valid.

Throws:

java.io.IOException - If the socket connection object is not valid (is null).

isConnectedToMaster

public boolean isConnectedToMaster()

Check if the repliation network is working. Tries to send a ping message to the master and returns the network status based on the success or failure of sending this message and receiving a pong reply. MT: Currently, only one thread is allowed to check the network status at any time to keep the code complexity down.

Returns:

true if the pong message was received before timing out after DEFAULT_PING_TIMEOUT millis, false otherwise

See Also:

DEFAULT_PING_TIMEOUT