org.jgroups.protocols

Class FRAG2

java.lang.Object

org.jgroups.stack.Protocol

org.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 (200 bytes).

Author:

Bela Ban

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected static class	FRAG2.FragEntry Class represents an entry for a message.

Field Summary

Fields

Modifier and Type	Field and Description
protected int	curr_id Used to assign fragmentation-specific sequence IDs (monotonically increasing)
protected int	frag_size
protected java.util.concurrent.ConcurrentMap<Address,java.util.concurrent.ConcurrentMap<java.lang.Long,FRAG2.FragEntry>>	fragment_list
protected Address	local_addr
protected java.util.List<Address>	members

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
FRAG2()

Method Summary

Modifier and Type	Method and Description
void	clearAllFragments()
void	clearFragmentsFor(Address mbr)
java.lang.Object	down(Event evt) Fragment a packet if larger than frag_size (add a header).
protected void	fragment(Message msg) Send all fragments as separate messages (with same ID !).
int	fragSize()
FRAG2	fragSize(int size)
int	getFragSize()
long	getNumberOfReceivedFragments()
long	getNumberOfSentFragments()
protected void	handleViewChange(View view)
void	init() Called after instance has been created (null constructor) and before protocol is started.
void	resetStats()
void	setFragSize(int s)
protected Message	unfragment(Message msg, FragHeader hdr) 1.
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

Field Detail

frag_size

protected int frag_size

fragment_list

protected final java.util.concurrent.ConcurrentMap<Address,java.util.concurrent.ConcurrentMap<java.lang.Long,FRAG2.FragEntry>> fragment_list

curr_id

protected int curr_id

Used to assign fragmentation-specific sequence IDs (monotonically increasing)

members

protected final java.util.List<Address> members

local_addr

protected Address local_addr

Constructor Detail

FRAG2

public FRAG2()

Method Detail

getFragSize

public int getFragSize()

setFragSize

public void setFragSize(int s)

getNumberOfSentFragments

public long getNumberOfSentFragments()

getNumberOfReceivedFragments

public long getNumberOfReceivedFragments()

fragSize

public int fragSize()

fragSize

public FRAG2 fragSize(int size)

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 fragmentation 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

handleViewChange

protected void handleViewChange(View view)

clearFragmentsFor

public void clearFragmentsFor(Address mbr)

clearAllFragments

public void clearAllFragments()

fragment

protected void fragment(Message msg)

Send all fragments as separate messages (with same ID !). Example:

     Given the generated ID is 2344, number of fragments=3, message {dst,src,buf}
     would be fragmented into:

     [2344,3,0]{dst,src,buf1},
     [2344,3,1]{dst,src,buf2} and
     [2344,3,2]{dst,src,buf3}
     

unfragment

protected Message unfragment(Message msg,
                             FragHeader hdr)

1. Get all the fragment buffers 2. When all are received -> Assemble them into one big buffer 3. Read headers and byte buffer from big buffer 4. Set headers and buffer in msg 5. Return the message