org.jgroups.protocols

Class 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 (1000 bytes).

Version:
$Id: FRAG2.java,v 1.9 2004/07/05 14:17:15 belaban Exp $
Author:
Bela Ban

Nested Class Summary

static class
FRAG2.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()
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 final String getName()
Overrides:
getName in interface Protocol

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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