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org.jgroups.protocols
Class NAKACK  

java.lang.Object
  org.jgroups.stack.Protocol
      org.jgroups.protocols.NAKACK

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public class NAKACK

extends org.jgroups.stack.Protocol

Negative AcKnowledgement layer (NAKs), paired with positive ACKs. The default is to send a message using NAKs: the sender sends messages with monotonically increasing seqnos, receiver requests retransmissions of missing messages (gaps). When a SWITCH_NAK_ACK event is received, the mode is switched to using NAK_ACKS: the sender still uses monotonically increasing seqnos, but the receiver acknowledges every message. NAK and NAK_ACK seqnos are the same, when switching the mode, the current seqno is reused. Both NAK and NAK_ACK messages use the current view ID in which the message is sent to queue messages destined for an upcoming view, or discard messages sent in a previous view. Both modes reset their seqnos to 0 when receiving a view change. The NAK_ACK scheme is used for broadcasting view changes.

The third mode is for out-of-band control messages (activated by SWITCH_OUT_OF_BAND): this mode does neither employ view IDs, nor does it use the same seqnos as NAK and NAK_ACK. It uses its own seqnos, unrelated to the ones used by NAK and NAK_ACK, and never resets them. In combination with the sender's address, this makes every out-of-band message unique. Out-of-band messages are used for example for broadcasting FLUSH messages.

Once a mode is set, it remains in effect until exactly 1 message has been sent, afterwards the default mode NAK is used again.

The following communication between 2 peers exists (left side is initiator, right side receiver):

 

 

 send_out_of_band
 -------------->       synchronous     (1)
 <-------------
 ack
 

 

 send_nak
 -------------->       asynchronous    (2)
 

 

 send_nak_ack
 -------------->       synchronous     (3)
 <--------------
 ack
 

 

 retransmit
 <--------------       asynchronous    (4)
 

 

 

When a message is sent, it will contain a header describing the type of the message, and containing additional data, such as sequence number etc. When a message is received, it is fed into either the OutOfBander or NAKer, depending on the header's type.

Note that in the synchronous modes, ACKs are sent for each request. If a reliable unicast protocol layer exists somewhere underneath this layer, then even the ACKs are transmitted reliably, thus increasing the number of messages exchanged. However, since it is envisaged that ACK/OUT_OF_BAND are not used frequently, this problem is currently not addressed.

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Nested Class Summary
(package private)  class	NAKACK.NAKer
(package private)  class	NAKACK.OutOfBander

 

Field Summary
(package private)  boolean	is_server
(package private)  org.jgroups.Address	local_addr
(package private)  java.util.Vector	members
(package private)  NAKACK.NAKer	naker
(package private)  NAKACK.OutOfBander	out_of_bander
(package private)  org.jgroups.util.List	queued_msgs
(package private)  long	rebroadcast_timeout
(package private)  long[]	retransmit_timeout
(package private)  boolean	send_next_msg_acking
(package private)  boolean	send_next_msg_out_of_band
(package private)  org.jgroups.util.TimeScheduler	timer
(package private)  org.jgroups.ViewId	vid
(package private)  org.jgroups.View	view
(package private) static java.lang.String	WRAPPED_MSG_KEY

 

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

NAKACK()

 

Method Summary
(package private)  boolean	coordinator()
(package private)  void	deliverQueuedMessages()           Deliver all messages in the queue where msg.vid == vid holds.
void	down(org.jgroups.Event evt)           Callback.
java.lang.String	getName()
void	init()           Do some initial tasks
java.util.Vector	providedDownServices()           List of events that are provided to layers below (they will be handled when sent down from below).
java.util.Vector	providedUpServices()           List of events that are provided to layers above (they will be handled when sent down from above).
(package private)  void	rebroadcastMsgs(java.util.Vector v)           Rebroadcasts the messages given as arguments
boolean	setProperties(java.util.Properties props)           Configures the protocol initially.
void	stop()           This method is called on a Channel.disconnect()>Channel.disconnect() 55 .
void	up(org.jgroups.Event evt)           Callback.

 

Methods inherited from class org.jgroups.stack.Protocol

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

retransmit_timeout

long[] retransmit_timeout

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naker

NAKACK.NAKer naker

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out_of_bander

NAKACK.OutOfBander out_of_bander

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vid

org.jgroups.ViewId vid

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view

org.jgroups.View view

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is_server

boolean is_server

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local_addr

org.jgroups.Address local_addr

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queued_msgs

final org.jgroups.util.List queued_msgs

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members

java.util.Vector members

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send_next_msg_out_of_band

boolean send_next_msg_out_of_band

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send_next_msg_acking

boolean send_next_msg_acking

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rebroadcast_timeout

long rebroadcast_timeout

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timer

org.jgroups.util.TimeScheduler timer

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WRAPPED_MSG_KEY

static final java.lang.String WRAPPED_MSG_KEY

See Also:

Constant Field Values

Constructor Detail

NAKACK

public NAKACK()

Method Detail

init

public void init()
          throws java.lang.Exception

Do some initial tasks

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stop

public void stop()

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

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

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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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providedDownServices

public java.util.Vector providedDownServices()

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

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

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up

public void up(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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down

public void down(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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coordinator

boolean coordinator()

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rebroadcastMsgs

void rebroadcastMsgs(java.util.Vector v)

Rebroadcasts the messages given as arguments

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deliverQueuedMessages

void deliverQueuedMessages()

Deliver all messages in the queue where msg.vid == vid holds. Messages were stored in the queue because their vid was greater than the current view.

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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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