org.jgroups.demos

Class QuoteServer

Implemented Interfaces:
MembershipListener, MessageListener

public class QuoteServer
extends java.lang.Object
implements MembershipListener, MessageListener

Example of a replicated quote server. The server maintains state which consists of a list of quotes and their corresponding values. When it is started, it tries to reach other quote servers to get its initial state. If it does not receive any response after 5 seconds, it assumes it is the first server and starts processing requests. When it receives a view notification it checks whether there are more members in the view than in its previous view. If this is the case, it broadcasts a request for the state to all members. Integration of different states is simply the union of all states (with the danger of overwriting mutually inconsistent state).

This mechanism allows both for fast discovery of initial servers, and - in the case of partition merging - for reintegration of existing servers. Broadcasting the state request upon every view change (only when new members are joined) causes potentially a lot of network traffic, but it is assumes that there will not be more than 5 quote servers at most.

Author:
Bela Ban

Method Summary

void
block()
Called whenever the member needs to stop sending messages.
Hashtable
getAllStocks()
float
getQuote(String stock_name)
byte[]
getState()
Answers the group state; e.g., when joining.
static void
main(args[] )
void
printAllStocks()
void
receive(Message msg)
Called when a message is received.
void
setQuote(String stock_name, Float value)
void
setState(byte[] state)
Sets the group state; e.g., when joining.
void
start()
void
suspect(Address suspected_mbr)
Called whenever a member is suspected of having crashed, but has not yet been excluded.
void
viewAccepted(View new_view)
Called when a change in membership has occurred.

Method Details

block

public void block()
Called whenever the member needs to stop sending messages. When the next view is received (viewAccepted()), the member can resume sending messages. If a member does not comply, the message(s) sent between a block() and a matching viewAccepted() callback will probably be delivered in the next view. The block() callback is only needed by the Virtual Synchrony suite of protocols (FLUSH protocol)3.2, otherwise it will never be invoked.
Specified by:
block in interface MembershipListener

getAllStocks

public Hashtable getAllStocks()

getQuote

public float getQuote(String stock_name)
            throws Exception

getState

public byte[] getState()
Answers the group state; e.g., when joining.
Specified by:
getState in interface MessageListener
Returns:
byte[]

main

public static void main(args[] )

printAllStocks

public void printAllStocks()

receive

public void receive(Message msg)
Called when a message is received.
Specified by:
receive in interface MessageListener
Parameters:
msg -

setQuote

public void setQuote(String stock_name,
                     Float value)

setState

public void setState(byte[] state)
Sets the group state; e.g., when joining.
Specified by:
setState in interface MessageListener
Parameters:
state -

start

public void start()

suspect

public void suspect(Address suspected_mbr)
Called whenever a member is suspected of having crashed, but has not yet been excluded.
Specified by:
suspect in interface MembershipListener

viewAccepted

public void viewAccepted(View new_view)
Called when a change in membership has occurred. No long running actions should be done in this callback. If some long running action needs to be performed, it should be done in a separate thread.
Specified by:
viewAccepted in interface MembershipListener

Copyright B) 1998-2005 Bela Ban. All Rights Reserved.