org.jgroups.protocols

Class 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 $

Authors:
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

Method Summary

void
down(Event evt)
Fragment a packet if larger than frag_size (add a header).
String
getName()
void
reset()
Just remove if you don't need to reset any state
boolean
setProperties(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, down, getDownProtocol, getDownQueue, getName, getProperties, getUpProtocol, getUpQueue, handleSpecialDownEvent, init, passDown, passUp, providedDownServices, providedUpServices, receiveDownEvent, receiveUpEvent, requiredDownServices, requiredUpServices, setDownProtocol, setObserver, setProperties, setPropertiesInternal, setProtocolStack, setUpProtocol, start, startDownHandler, startUpHandler, stop, stopInternal, up

Method Details

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 interface Protocol


getName

public String getName()
Overrides:
getName in interface Protocol


reset

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


setProperties

public boolean setProperties(Properties props)
Setup the Protocol instance acording to the configuration string
Overrides:
setProperties in interface 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 interface Protocol


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