org.jgroups.protocols
Class FRAG2

java.lang.Object
  extended byorg.jgroups.stack.Protocol
      extended byorg.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 (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
 
Constructor Summary
FRAG2()
           
 
Method Summary
 void down(Event evt)
          Fragment a packet if larger than frag_size (add a header).
 java.lang.String getName()
           
 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

FRAG2

public FRAG2()
Method Detail

getName

public final 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

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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