org.jgroups.protocols

Class STATE_TRANSFER

Implemented Interfaces:
RequestHandler

public class STATE_TRANSFER
extends Protocol
implements RequestHandler

State transfer layer. Upon receiving a GET_STATE event from JChannel, a MAKE_COPY message is sent to all members. When the originator receives MAKE_COPY, it queues all messages to the channel. When another member receives the message, it asks the JChannel to provide it with a copy of the current state (GetStateEvent is received by application, returnState() sends state down the stack). Then the current layer sends a unicast RETURN_STATE message to the coordinator, which returns the cached copy. When the state is received by the originator, the GET_STATE sender is unblocked with a GET_STATE_OK event up the stack (unless it already timed out).

Requires QUEUE layer on top.

Author:
Bela Ban

Field Summary

Fields inherited from class org.jgroups.stack.Protocol

down_handler, down_prot, down_queue, down_thread, down_thread_prio, log, observer, props, stack, stats, trace, up_handler, up_prot, up_queue, up_thread, up_thread_prio, warn

Method Summary

void
down(Event evt)
An event is to be sent down the stack.
String
getName()
All protocol names have to be unique !
Object
handle(Message msg)
void
init()
Called after instance has been created (null constructor) and before protocol is started.
Vector
requiredUpServices()
List of events that are required to be answered by some layer above.
boolean
setProperties(Properties props)
Configures the protocol initially.
void
start()
This method is called on a Channel.connect(String).
void
stop()
This method is called on a Channel.disconnect().
void
up(Event evt)
An event was received from the layer below.

Methods inherited from class org.jgroups.stack.Protocol

destroy, down, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getDownQueue, getName, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, init, isTrace, isWarn, passDown, passUp, printStats, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, resetStats, setDownProtocol, setObserver, setProperties, setPropertiesInternal, setProtocolStack, setTrace, setUpProtocol, setWarn, start, startDownHandler, startUpHandler, statsEnabled, stop, stopInternal, up, upThreadEnabled

Method Details

down

public void down(Event evt)
An event is to be sent down the stack. The layer may want to examine its type and perform some action on it, depending on the event's type. If the event is a message MSG, then the layer may need to add a header to it (or do nothing at all) before sending it down the stack using passDown(). In case of a GET_ADDRESS event (which tries to retrieve the stack's address from one of the bottom layers), the layer may need to send a new response event back up the stack using passUp().
Overrides:
down in interface Protocol

getName

public String getName()
All protocol names have to be unique !
Overrides:
getName in interface Protocol

handle

public Object handle(Message msg)
Specified by:
handle in interface RequestHandler

init

public void init()
            throws Exception
Called after instance has been created (null constructor) and before protocol is started. Properties are already set. Other protocols are not yet connected and events cannot yet be sent.
Overrides:
init in interface Protocol

requiredUpServices

public Vector requiredUpServices()
List of events that are required to be answered by some layer above.
Overrides:
requiredUpServices in interface Protocol
Returns:
Vector (of Integers)

setProperties

public boolean setProperties(Properties props)
Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:
 "loopback=false;unicast_inport=4444"
 
Overrides:
setProperties in interface Protocol

start

public void start()
            throws Exception
This method is called on a Channel.connect(String). Starts work. Protocols are connected and queues are ready to receive events. Will be called from bottom to top. This call will replace the START and START_OK events.
Overrides:
start in interface Protocol

stop

public void stop()
This method is called on a Channel.disconnect(). Stops work (e.g. by closing multicast socket). Will be called from top to bottom. This means that at the time of the method invocation the neighbor protocol below is still working. This method will replace the STOP, STOP_OK, CLEANUP and CLEANUP_OK events. The ProtocolStack guarantees that when this method is called all messages in the down queue will have been flushed
Overrides:
stop in interface Protocol

up

public void up(Event evt)
An event was received from the layer below. Usually the current layer will want to examine the event type and - depending on its type - perform some computation (e.g. removing headers from a MSG event type, or updating the internal membership list when receiving a VIEW_CHANGE event). Finally the event is either a) discarded, or b) an event is sent down the stack using passDown() or c) the event (or another event) is sent up the stack using passUp().
Overrides:
up in interface Protocol

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