org.jgroups.protocols

Class FRAG

java.lang.Object

org.jgroups.stack.Protocol

org.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 added to the messages as a header (and removed at the receiving side).

Contrary to FRAG2, FRAG marshals the entire message (including the headers) into a byte[] buffer and the fragments that buffer. Because Message.size() is called rather than Message.getLength(), and because of the overhead of marshalling, this will be slower than FRAG2.

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.

Author:

Bela Ban, Filip Hanik

Field Summary

Fields inherited from class org.jgroups.stack.Protocol

after_creation_hook, down_prot, ergonomics, id, log, name, stack, stats, up_prot

Constructor Summary

Constructors

Constructor and Description
FRAG()

Method Summary

Modifier and Type	Method and Description
java.lang.Object	down(Event evt) Fragment a packet if larger than frag_size (add a header).
int	getFragSize()
long	getNumberOfReceivedFragments()
long	getNumberOfReceivedMessages()
long	getNumberOfSentFragments()
long	getNumberOfSentMessages()
void	init() Called after instance has been created (null constructor) and before protocol is started.
void	resetStats()
void	setFragSize(int s)
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.
void	up(MessageBatch batch) Sends up a multiple messages in a MessageBatch.

Methods inherited from class org.jgroups.stack.Protocol

accept, afterCreationHook, destroy, dumpStats, enableStats, getConfigurableObjects, getDownProtocol, getDownServices, getId, getIdsAbove, getLevel, getLog, getName, getProtocolStack, getSocketFactory, getThreadFactory, getTransport, getUpProtocol, getUpServices, getValue, isErgonomics, level, parse, printStats, providedDownServices, providedUpServices, requiredDownServices, requiredUpServices, resetStatistics, setDownProtocol, setErgonomics, setId, setLevel, setProtocolStack, setSocketFactory, setUpProtocol, setValue, setValues, start, statsEnabled, stop

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

getFragSize

public int getFragSize()

setFragSize

public void setFragSize(int s)

getNumberOfSentMessages

public long getNumberOfSentMessages()

getNumberOfSentFragments

public long getNumberOfSentFragments()

getNumberOfReceivedMessages

public long getNumberOfReceivedMessages()

getNumberOfReceivedFragments

public long getNumberOfReceivedFragments()

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

up

public void up(MessageBatch batch)

Description copied from class: Protocol

Sends up a multiple messages in a MessageBatch. The sender of the batch is always the same, and so is the destination (null == multicast messages). Messages in a batch can be OOB messages, regular messages, or mixed messages, although the transport itself will create initial MessageBatches that contain only either OOB or regular messages.

The default processing below sends messages up the stack individually, based on a matching criteria (calling Protocol.accept(org.jgroups.Message)), and - if true - calls Protocol.up(org.jgroups.Event) for that message and removes the message. If the batch is not empty, it is passed up, or else it is dropped.

Subclasses should check if there are any messages destined for them (e.g. using MessageBatch.getMatchingMessages(short,boolean)), then possibly remove and process them and finally pass the batch up to the next protocol. Protocols can also modify messages in place, e.g. ENCRYPT could decrypt all encrypted messages in the batch, not remove them, and pass the batch up when done.

Overrides:

up in class Protocol

Parameters:

batch - The message batch