org.jgroups.protocols
Class FRAG2

java.lang.Object
  extended by org.jgroups.stack.Protocol
      extended by org.jgroups.protocols.FRAG2

public class FRAG2
extends Protocol

Fragmentation layer. Fragments messages larger than frag_size into smaller packets. Reassembles fragmented packets into bigger ones. The fragmentation number is prepended to the messages as a header (and removed at the receiving side).

Each fragment is identified by (a) the sender (part of the message to which the header is appended), (b) the fragmentation ID (which is unique per FRAG2 layer (monotonically increasing) and (c) the fragement ID which ranges from 0 to number_of_fragments-1.

Requirement: lossless delivery (e.g. NAK, ACK). No requirement on ordering. Works for both unicast and multicast messages.
Compared to FRAG, this protocol does not need to serialize the message in order to break it into smaller fragments: it looks only at the message's buffer, which is a byte[] array anyway. We assume that the size addition for headers and src and dest address is minimal when the transport finally has to serialize the message, so we add a constant (200 bytes).

Version:
$Id: FRAG2.java,v 1.36.2.1 2008/07/22 11:51:22 belaban Exp $
Author:
Bela Ban

Field Summary
 
Fields inherited from class org.jgroups.stack.Protocol
down_prot, log, props, stack, stats, up_prot
 
Constructor Summary
FRAG2()
           
 
Method Summary
 java.lang.Object down(Event evt)
          Fragment a packet if larger than frag_size (add a header).
 int getFragSize()
           
 java.lang.String getName()
           
 long getNumberOfReceivedFragments()
           
 long getNumberOfReceivedMessages()
           
 long getNumberOfSentFragments()
           
 long getNumberOfSentMessages()
           
 int getOverhead()
           
 void init()
          Called after instance has been created (null constructor) and before protocol is started.
 void resetStats()
           
 void setFragSize(int s)
           
 void setOverhead(int o)
           
 boolean setProperties(java.util.Properties props)
          Setup the Protocol instance acording to the configuration string
 java.lang.Object up(Event evt)
          If event is a message, if it is fragmented, re-assemble fragments into big message and pass up the stack.
 
Methods inherited from class org.jgroups.stack.Protocol
destroy, downThreadEnabled, dumpStats, enableStats, getDownProtocol, getProperties, getProtocolStack, getThreadFactory, getTransport, getUpProtocol, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, setDownProtocol, setPropertiesInternal, setProtocolStack, setUpProtocol, start, statsEnabled, stop, upThreadEnabled
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FRAG2

public FRAG2()
Method Detail

getName

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

getFragSize

public int getFragSize()

setFragSize

public void setFragSize(int s)

getOverhead

public int getOverhead()

setOverhead

public void setOverhead(int o)

getNumberOfSentMessages

public long getNumberOfSentMessages()

getNumberOfSentFragments

public long getNumberOfSentFragments()

getNumberOfReceivedMessages

public long getNumberOfReceivedMessages()

getNumberOfReceivedFragments

public long getNumberOfReceivedFragments()

setProperties

public boolean setProperties(java.util.Properties props)
Setup the Protocol instance acording to the configuration string

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

resetStats

public void resetStats()
Overrides:
resetStats in class Protocol

down

public java.lang.Object down(Event evt)
Fragment a packet if larger than frag_size (add a header). Otherwise just pass down. Only add a header if framentation is needed !

Overrides:
down in class Protocol

up

public java.lang.Object up(Event evt)
If event is a message, if it is fragmented, re-assemble fragments into big message and pass up the stack.

Overrides:
up in class Protocol


Copyright ? 1998-2008 Bela Ban. All Rights Reserved.