org.jgroups.protocols.pbcast
Class FLUSH

java.lang.Object
  extended by org.jgroups.stack.Protocol
      extended by org.jgroups.protocols.pbcast.FLUSH

public class FLUSH
extends Protocol

Flush, as it name implies, forces group members to flush their pending messages while blocking them to send any additional messages. The process of flushing acquiesces the group so that state transfer or a join can be done. It is also called stop-the-world model as nobody will be able to send messages while a flush is in process.

Flush is needed for:

(1) State transfer. When a member requests state transfer, the coordinator tells everyone to stop sending messages and waits for everyone's ack. Then it asks the application for its state and ships it back to the requester. After the requester has received and set the state successfully, the coordinator tells everyone to resume sending messages.

(2) View changes (e.g.a join). Before installing a new view V2, flushing would ensure that all messages *sent* in the current view V1 are indeed *delivered* in V1, rather than in V2 (in all non-faulty members). This is essentially Virtual Synchrony.

Since:
2.4
Version:
$Id$
Author:
Vladimir Blagojevic

Nested Class Summary
static class FLUSH.FlushHeader
           
 
Field Summary
static java.lang.String NAME
           
 
Fields inherited from class org.jgroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, log, observer, props, stack, stats, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
FLUSH()
           
 
Method Summary
 void down(Event evt)
          An event is to be sent down the stack.
 double getAverageFlushDuration()
           
 java.lang.String getName()
           
 int getNumberOfFlushes()
           
 long getTotalTimeInFlush()
           
 void init()
          Called after instance has been created (null constructor) and before protocol is started.
 java.util.Vector providedDownServices()
          List of events that are provided to layers below (they will be handled when sent down from below).
 boolean setProperties(java.util.Properties props)
          Configures the protocol initially.
 void start()
          This method is called on a Channel.connect(String).
 boolean startFlush(long timeout)
           
 void stop()
          This method is called on a Channel.disconnect().
 void stopFlush()
           
 void up(Event evt)
          An event was received from the layer below.
 
Methods inherited from class org.jgroups.stack.Protocol
destroy, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, passDown, passUp, printStats, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, resetStats, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, statsEnabled, stopInternal, upThreadEnabled
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

NAME

public static final java.lang.String NAME
See Also:
Constant Field Values
Constructor Detail

FLUSH

public FLUSH()
Method Detail

getName

public java.lang.String getName()
Specified by:
getName in class Protocol

setProperties

public boolean setProperties(java.util.Properties props)
Description copied from class: Protocol
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 class Protocol

init

public void init()
          throws java.lang.Exception
Description copied from class: Protocol
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 class Protocol
Throws:
java.lang.Exception - Thrown if protocol cannot be initialized successfully. This will cause the ProtocolStack to fail, so the channel constructor will throw an exception

start

public void start()
           throws java.lang.Exception
Description copied from class: Protocol
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 class Protocol
Throws:
java.lang.Exception - Thrown if protocol cannot be started successfully. This will cause the ProtocolStack to fail, so Channel.connect(String) will throw an exception

stop

public void stop()
Description copied from class: Protocol
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 class Protocol

getAverageFlushDuration

public double getAverageFlushDuration()

getTotalTimeInFlush

public long getTotalTimeInFlush()

getNumberOfFlushes

public int getNumberOfFlushes()

startFlush

public boolean startFlush(long timeout)

stopFlush

public void stopFlush()

down

public void down(Event evt)
Description copied from class: Protocol
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 class Protocol

up

public void up(Event evt)
Description copied from class: Protocol
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 class Protocol

providedDownServices

public java.util.Vector providedDownServices()
Description copied from class: Protocol
List of events that are provided to layers below (they will be handled when sent down from below).

Overrides:
providedDownServices in class Protocol
Returns:
Vector (of Integers)


Copyright ? 1998-2006 Bela Ban. All Rights Reserved.