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org.jgroups.protocols
Class FLUSH  

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.stack.MessageProtocol
          org.jgroups.stack.RpcProtocol
              org.jgroups.protocols.FLUSH

All Implemented Interfaces:

org.jgroups.blocks.RequestHandler

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public class FLUSH

extends org.jgroups.stack.RpcProtocol

The task of the FLUSH protocol is to flush all pending messages out of the system. This is done before a view change by stopping all senders and then agreeing on what messages should be delivered in the current view (before switching to the new view). A coordinator broadcasts a FLUSH message. The message contains an array of the highest sequence number for each member as seen by the coordinator so far. Each member responds with its highest sequence numbers seen so far (for each member): if its sequence number for a member P is higher than the one sent by the coordinator, it will append the messages apparently not received by the coordinator to its reply. The coordinator (when all replies have been received), computes for each member the lowest and highest sequence number and re-broadcasts messages accordingly (using ACKs rather then NAKs to ensure reliable delivery).

Example:

   FLUSH  ---> (p=10, q=22, r=7)

   <-- (p=10, q=20, r=7)    (did not receive 2 messages from q)
   <-- (p=12, q=23, r=7)    (attached are messages p11, p12, and q23)
   <-- (p=10, q=22, r=8)    (attached is message r8)
   ---------------------
   min:   11    21    8
   max:   12    23    8
   

The coordinator now computes the range for each member and re-broadcasts messages p11, p12, q21, q22, q23 and r8. This is essentially the exclusive min and inclusive max of all replies. Note that messages p11, p12 and q23 were not received by the coordinator itself before. They were only returned as result of the FLUSH replies and the coordinator now re-broadcasts them.

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Field Summary
(package private)  java.lang.Object	block_mutex
(package private)  long	block_timeout
(package private)  boolean	blocked
(package private)  Digest	digest
(package private)  java.lang.Object	digest_mutex
(package private)  long	digest_timeout
(package private)  org.jgroups.util.List	get_msgs
(package private)  java.lang.Object	get_msgs_mutex
(package private)  long	get_msgs_timeout
(package private)  long[]	highest_delivered_msgs
(package private)  java.lang.Object	highest_delivered_mutex
(package private)  boolean	is_server
(package private)  org.jgroups.Address	local_addr
(package private)  java.util.Vector	mbrs

 

Fields inherited from class org.jgroups.stack.MessageProtocol

_corr, members

 

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

 

Constructor Summary

FLUSH()

 

Method Summary
private  FlushRsp	flush(java.util.Vector dests)           Triggered by reception of FLUSH event from GMS layer (must be coordinator).
(package private)  void	getHighestDeliveredSeqnos()           Returns the highest seqnos (for each member) seen so far (using the NAKACK layer)
(package private)  void	getMessageDigest(long[] highest_seqnos)           Interacts with a lower layer to retrieve unstable messages (e.g.
java.lang.String	getName()
boolean	handleDownEvent(org.jgroups.Event evt)           Callback.
Digest	handleFlush(java.util.Vector flush_dests, long[] highest_seqnos)           Called by coordinator running the FLUSH protocol.
boolean	handleUpEvent(org.jgroups.Event evt)           Callback.
java.util.Vector	providedUpServices()           List of events that are provided to layers above (they will be handled when sent down from above).
void	receiveDownEvent(org.jgroups.Event evt)           The default handling adds the event to the down-queue where events are handled in order of addition by a thread.
java.util.Vector	requiredDownServices()           List of events that are required to be answered by some layer below.
boolean	setProperties(java.util.Properties props)           Configures the protocol initially.
void	start()           This method is called on a Channel.connect(String)>Channel.connect(String) 55 .

 

Methods inherited from class org.jgroups.stack.RpcProtocol

callRemoteMethod, callRemoteMethod, callRemoteMethod, callRemoteMethod, callRemoteMethods, callRemoteMethods, callRemoteMethods, handle

 

Methods inherited from class org.jgroups.stack.MessageProtocol

castMessage, down, sendMessage, stop, up, updateView

 

Methods inherited from class org.jgroups.stack.Protocol

destroy, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, init, isTrace, isWarn, passDown, passUp, printStats, providedDownServices, receiveUpEvent, requiredUpServices, resetStats, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setTrace, setUpProtocol, setWarn, 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

mbrs

final java.util.Vector mbrs

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is_server

boolean is_server

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block_mutex

final java.lang.Object block_mutex

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block_timeout

long block_timeout

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local_addr

org.jgroups.Address local_addr

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blocked

boolean blocked

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digest_mutex

final java.lang.Object digest_mutex

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digest_timeout

long digest_timeout

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highest_delivered_mutex

final java.lang.Object highest_delivered_mutex

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highest_delivered_msgs

long[] highest_delivered_msgs

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digest

Digest digest

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get_msgs_mutex

final java.lang.Object get_msgs_mutex

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get_msgs_timeout

final long get_msgs_timeout

See Also:

Constant Field Values

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get_msgs

org.jgroups.util.List get_msgs

Constructor Detail

FLUSH

public FLUSH()

Method Detail

getName

public java.lang.String getName()

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providedUpServices

public java.util.Vector providedUpServices()

Description copied from class: org.jgroups.stack.Protocol

List of events that are provided to layers above (they will be handled when sent down from above).

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requiredDownServices

public java.util.Vector requiredDownServices()

Description copied from class: org.jgroups.stack.Protocol

List of events that are required to be answered by some layer below.

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start

public void start()
           throws java.lang.Exception

Description copied from class: org.jgroups.stack.Protocol

This method is called on a Channel.connect(String)>Channel.connect(String) 55 . 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.

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flush

private FlushRsp flush(java.util.Vector dests)

Triggered by reception of FLUSH event from GMS layer (must be coordinator). Calls HandleFlush in all members and returns FLUSH_OK event.

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handleFlush

public Digest handleFlush(java.util.Vector flush_dests,
                          long[] highest_seqnos)

Called by coordinator running the FLUSH protocol. Argument is an array of the highest seqnos as seen by the coordinator (for each member). handleFlush() checks for each member its own highest seqno seen for that member. If it is higher than the one seen by the coordinator, all higher messages are attached to the return value (a message digest).

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getHighestDeliveredSeqnos

void getHighestDeliveredSeqnos()

Returns the highest seqnos (for each member) seen so far (using the NAKACK layer)

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getMessageDigest

void getMessageDigest(long[] highest_seqnos)

Interacts with a lower layer to retrieve unstable messages (e.g. NAKACK)

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handleUpEvent

public boolean handleUpEvent(org.jgroups.Event evt)

Callback. Called by superclass when event may be handled.

Do not use PassUp in this method as the event is passed up by default by the superclass after this method returns !

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handleDownEvent

public boolean handleDownEvent(org.jgroups.Event evt)

Callback. Called by superclass when event may be handled.

Do not use PassDown in this method as the event is passed down by default by the superclass after this method returns !

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receiveDownEvent

public void receiveDownEvent(org.jgroups.Event evt)

The default handling adds the event to the down-queue where events are handled in order of addition by a thread. However, there exists a deadlock between the FLUSH and BLOCK_OK down events: when a FLUSH event is received, a BLOCK is sent up, which triggers a BLOCK_OK event to be sent down to be handled by the FLUSH layer. However, the FLUSH layer's thread is still processing the FLUSH down event and is therefore blocked, waiting for a BLOCK_OK event. Therefore, the BLOCK_OK event has to 'preempt' the FLUSH event processing. This is done by overriding this method: when a BLOCK_OK event is received, it is processed immediately (in parallel to the FLUSH event), which causes the FLUSH event processing to return.

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setProperties

public boolean setProperties(java.util.Properties props)

Description copied from class: org.jgroups.stack.Protocol

Configures the protocol initially. A configuration string consists of name=value items, separated by a ';' (semicolon), e.g.:

 "loopback=false;unicast_inport=4444"
 

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> jgroups >> [ protocols overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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