org.jgroups.protocols
Class FRAG

java.lang.Object
  extended byorg.jgroups.stack.Protocol
      extended byorg.jgroups.protocols.FRAG

public class FRAG
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 FRAG 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.

Typical stack:

 FIFO
 FRAG
 NAK
 UDP
 

Version:
$Id: FRAG.java,v 1.11 2004/07/05 14:17:15 belaban Exp $
Author:
Bela Ban, Filip Hanik

Nested Class Summary
static class FRAG.FragHeader
           
 
Field Summary
 
Fields inherited from class org.jgroups.stack.Protocol
down_handler, down_prot, down_queue, down_thread, down_thread_prio, log, observer, props, stack, up_handler, up_prot, up_queue, up_thread, up_thread_prio
 
Constructor Summary
FRAG()
           
 
Method Summary
 void down(Event evt)
          Fragment a packet if larger than frag_size (add a header).
 java.lang.String getName()
           
 void reset()
          Just remove if you don't need to reset any state
 boolean setProperties(java.util.Properties props)
          Setup the Protocol instance acording to the configuration string
 void 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, getDownProtocol, getDownQueue, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setPropertiesInternal, setProtocolStack, setUpProtocol, start, startDownHandler, startUpHandler, stop, stopInternal
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FRAG

public FRAG()
Method Detail

getName

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

setProperties

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

Overrides:
setProperties in class Protocol

reset

public void reset()
Just remove if you don't need to reset any state


down

public void 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 void up(Event evt)
If event is a message, if it is fragmented, re-assemble fragments into big message and pass up the stack. todo: Filip catch the view change event so that we can clean up old members

Overrides:
up in class Protocol


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