org.javagroups.protocols.pbcast
Class NAKACK

java.lang.Object
  |
  +--org.javagroups.stack.Protocol
        |
        +--org.javagroups.protocols.pbcast.NAKACK
All Implemented Interfaces:
Retransmitter.RetransmitCommand

public class NAKACK
extends Protocol
implements Retransmitter.RetransmitCommand

Negative AcKnowledgement layer (NAKs). Messages are assigned a monotonically increasing sequence number (seqno). Receivers deliver messages ordered according to seqno and request retransmission of missing messages. Retransmitted messages are bundled into bigger ones, e.g. when getting an xmit request for messages 1-10, instead of sending 10 unicast messages, we bundle all 10 messages into 1 and send it. However, since this protocol typically sits below FRAG, we cannot count on FRAG to fragement/defragment the (possibly) large message into smaller ones. Therefore we only bundle messages up to max_xmit_size bytes to prevent too large messages. For example, if the bundled message size was a total of 34000 bytes, and max_xmit_size=16000, we'd send 3 messages: 2 16K and a 2K message. Note that max_xmit_size should be the same value as FRAG.frag_size (or smaller).

Author:
Bela Ban

Field Summary
 
Fields inherited from class org.javagroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, observer, props, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
NAKACK()
           
 
Method Summary
 void down(Event evt)
          Callback.
 java.lang.String getName()
           
 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).
 void retransmit(long first_seqno, long last_seqno, Address sender)
          Implementation of Retransmitter.RetransmitCommand.
 boolean setProperties(java.util.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)
          Callback.
 
Methods inherited from class org.javagroups.stack.Protocol
destroy, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, init, passDown, passUp, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, startDownHandler, startUpHandler, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

NAKACK

public NAKACK()
Method Detail

getName

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

providedUpServices

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

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

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)

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

down

public void down(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 !

Overrides:
down in class Protocol

up

public void up(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 !

Overrides:
up 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

retransmit

public void retransmit(long first_seqno,
                       long last_seqno,
                       Address sender)
Implementation of Retransmitter.RetransmitCommand. Called by retransmission thread when gap is detected. Sends XMIT_REQ to originator of msg

Specified by:
retransmit in interface Retransmitter.RetransmitCommand
Parameters:
first_seqno - The sequence number of the first missing message
last_seqno - The sequence number of the last missing message
sender - The destination of the member to which the retransmit request will be sent (nak-based scheme), or to which the message will be retransmitted (ack-based scheme).


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