package org.jgroups.protocols;
import org.jgroups.Address;
import org.jgroups.Event;
import org.jgroups.Message;
import org.jgroups.View;
import org.jgroups.stack.Protocol;
import org.jgroups.util.Range;
import org.jgroups.util.Util;
import java.util.*;
/**
* 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).<p>
* 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.<p>
* Requirement: lossless delivery (e.g. NAK, ACK). No requirement on ordering. Works for both unicast and
* multicast messages.<br/>
* Compared to FRAG, this protocol does <em>not</em> 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
* @version $Id: FRAG2.java,v 1.25 2006/08/23 07:20:12 belaban Exp $
*/
public class FRAG2 extends Protocol {
/** The max number of bytes in a message. If a message's buffer is bigger, it will be fragmented */
int frag_size=1500;
/** Number of bytes that we think the headers plus src and dest will take up when
message is serialized by transport. This will be subtracted from frag_size */
int overhead=200;
/*the fragmentation list contains a fragmentation table per sender
*this way it becomes easier to clean up if a sender (member) leaves or crashes
*/
private final FragmentationList fragment_list=new FragmentationList();
private int curr_id=1;
private final Vector members=new Vector(11);
private static final String name="FRAG2";
long num_sent_msgs=0;
long num_sent_frags=0;
long num_received_msgs=0;
long num_received_frags=0;
public final String getName() {
return name;
}
public int getFragSize() {return frag_size;}
public void setFragSize(int s) {frag_size=s;}
public int getOverhead() {return overhead;}
public void setOverhead(int o) {overhead=o;}
public long getNumberOfSentMessages() {return num_sent_msgs;}
public long getNumberOfSentFragments() {return num_sent_frags;}
public long getNumberOfReceivedMessages() {return num_received_msgs;}
public long getNumberOfReceivedFragments() {return num_received_frags;}
synchronized int getNextId() {
return curr_id++;
}
/** Setup the Protocol instance acording to the configuration string */
public boolean setProperties(Properties props) {
String str;
super.setProperties(props);
str=props.getProperty("frag_size");
if(str != null) {
frag_size=Integer.parseInt(str);
props.remove("frag_size");
}
str=props.getProperty("overhead");
if(str != null) {
overhead=Integer.parseInt(str);
props.remove("overhead");
}
int old_frag_size=frag_size;
frag_size-=overhead;
if(frag_size <=0) {
log.error("frag_size=" + old_frag_size + ", overhead=" + overhead +
", new frag_size=" + frag_size + ": new frag_size is invalid");
return false;
}
if(log.isInfoEnabled())
log.info("frag_size=" + old_frag_size + ", overhead=" + overhead + ", new frag_size=" + frag_size);
if(props.size() > 0) {
log.error("FRAG2.setProperties(): the following properties are not recognized: " + props);
return false;
}
return true;
}
public void resetStats() {
super.resetStats();
num_sent_msgs=num_sent_frags=num_received_msgs=num_received_frags=0;
}
/**
* Fragment a packet if larger than frag_size (add a header). Otherwise just pass down. Only
* add a header if framentation is needed !
*/
public void down(Event evt) {
switch(evt.getType()) {
case Event.MSG:
Message msg=(Message)evt.getArg();
long size=msg.getLength();
synchronized(this) {
num_sent_msgs++;
}
if(size > frag_size) {
if(trace) {
StringBuffer sb=new StringBuffer("message's buffer size is ");
sb.append(size).append(", will fragment ").append("(frag_size=");
sb.append(frag_size).append(')');
log.trace(sb.toString());
}
fragment(msg); // Fragment and pass down
return;
}
break;
case Event.VIEW_CHANGE:
//don't do anything if this dude is sending out the view change
//we are receiving a view change,
//in here we check for the
View view=(View)evt.getArg();
Vector new_mbrs=view.getMembers(), left_mbrs;
Address mbr;
left_mbrs=Util.determineLeftMembers(members, new_mbrs);
members.clear();
members.addAll(new_mbrs);
for(int i=0; i < left_mbrs.size(); i++) {
mbr=(Address)left_mbrs.elementAt(i);
//the new view doesn't contain the sender, he must have left,
//hence we will clear all his fragmentation tables
fragment_list.remove(mbr);
if(trace) log.trace("[VIEW_CHANGE] removed " + mbr + " from fragmentation table");
}
break;
case Event.CONFIG:
passDown(evt);
if(log.isDebugEnabled()) log.debug("received CONFIG event: " + evt.getArg());
handleConfigEvent((HashMap)evt.getArg());
return;
}
passDown(evt); // Pass on to the layer below us
}
/**
* If event is a message, if it is fragmented, re-assemble fragments into big message and pass up
* the stack.
*/
public void up(Event evt) {
switch(evt.getType()) {
case Event.MSG:
Message msg=(Message)evt.getArg();
Object obj=msg.getHeader(name);
if(obj != null && obj instanceof FragHeader) { // needs to be defragmented
unfragment(msg); // Unfragment and possibly pass up
return;
}
else {
num_received_msgs++;
}
break;
case Event.CONFIG:
passUp(evt);
if(log.isInfoEnabled()) log.info("received CONFIG event: " + evt.getArg());
handleConfigEvent((HashMap)evt.getArg());
return;
}
passUp(evt); // Pass up to the layer above us by default
}
/** Send all fragments as separate messages (with same ID !).
Example:
<pre>
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}
</pre>
*/
void fragment(Message msg) {
byte[] buffer;
List fragments;
Event evt;
FragHeader hdr;
Message frag_msg;
Address dest=msg.getDest();
long id=getNextId(); // used as seqnos
int num_frags;
StringBuffer sb;
Range r;
try {
buffer=msg.getBuffer();
fragments=Util.computeFragOffsets(buffer, frag_size);
num_frags=fragments.size();
synchronized(this) {
num_sent_frags+=num_frags;
}
if(trace) {
sb=new StringBuffer("fragmenting packet to ");
sb.append((dest != null ? dest.toString() : "<all members>")).append(" (size=").append(buffer.length);
sb.append(") into ").append(num_frags).append(" fragment(s) [frag_size=").append(frag_size).append(']');
log.trace(sb.toString());
}
for(int i=0; i < fragments.size(); i++) {
r=(Range)fragments.get(i);
// Copy the original msg (needed because we need to copy the headers too)
frag_msg=msg.copy(false); // don't copy the buffer, only src, dest and headers
frag_msg.setBuffer(buffer, (int)r.low, (int)r.high);
hdr=new FragHeader(id, i, num_frags);
frag_msg.putHeader(name, hdr);
evt=new Event(Event.MSG, frag_msg);
passDown(evt);
}
}
catch(Exception e) {
if(log.isErrorEnabled()) log.error("fragmentation failure", e);
}
}
/**
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. Pass msg up the stack
*/
void unfragment(Message msg) {
FragmentationTable frag_table;
Address sender=msg.getSrc();
Message assembled_msg;
FragHeader hdr=(FragHeader)msg.removeHeader(name);
frag_table=fragment_list.get(sender);
if(frag_table == null) {
frag_table=new FragmentationTable(sender);
try {
fragment_list.add(sender, frag_table);
}
catch(IllegalArgumentException x) { // the entry has already been added, probably in parallel from another thread
frag_table=fragment_list.get(sender);
}
}
num_received_frags++;
assembled_msg=frag_table.add(hdr.id, hdr.frag_id, hdr.num_frags, msg);
if(assembled_msg != null) {
try {
if(trace) log.trace("assembled_msg is " + assembled_msg);
assembled_msg.setSrc(sender); // needed ? YES, because fragments have a null src !!
num_received_msgs++;
passUp(new Event(Event.MSG, assembled_msg));
}
catch(Exception e) {
if(log.isErrorEnabled()) log.error("unfragmentation failed", e);
}
}
}
void handleConfigEvent(HashMap map) {
if(map == null) return;
if(map.containsKey("frag_size")) {
frag_size=((Integer)map.get("frag_size")).intValue();
if(log.isDebugEnabled()) log.debug("setting frag_size=" + frag_size);
}
}
/**
* A fragmentation list keeps a list of fragmentation tables
* sorted by an Address ( the sender ).
* This way, if the sender disappears or leaves the group half way
* sending the content, we can simply remove this members fragmentation
* table and clean up the memory of the receiver.
* We do not have to do the same for the sender, since the sender doesn't keep a fragmentation table
*/
static class FragmentationList {
/* * HashMap<Address,FragmentationTable>, initialize the hashtable to hold all the fragmentation
* tables (11 is the best growth capacity to start with)
*/
private final HashMap frag_tables=new HashMap(11);
/**
* Adds a fragmentation table for this particular sender
* If this sender already has a fragmentation table, an IllegalArgumentException
* will be thrown.
* @param sender - the address of the sender, cannot be null
* @param table - the fragmentation table of this sender, cannot be null
* @exception IllegalArgumentException if an entry for this sender already exist
*/
public void add(Address sender, FragmentationTable table) throws IllegalArgumentException {
FragmentationTable healthCheck;
synchronized(frag_tables) {
healthCheck=(FragmentationTable)frag_tables.get(sender);
if(healthCheck == null) {
frag_tables.put(sender, table);
}
else {
throw new IllegalArgumentException("Sender <" + sender + "> already exists in the fragementation list.");
}
}
}
/**
* returns a fragmentation table for this sender
* returns null if the sender doesn't have a fragmentation table
* @return the fragmentation table for this sender, or null if no table exist
*/
public FragmentationTable get(Address sender) {
synchronized(frag_tables) {
return (FragmentationTable)frag_tables.get(sender);
}
}
/**
* returns true if this sender already holds a
* fragmentation for this sender, false otherwise
* @param sender - the sender, cannot be null
* @return true if this sender already has a fragmentation table
*/
public boolean containsSender(Address sender) {
synchronized(frag_tables) {
return frag_tables.containsKey(sender);
}
}
/**
* removes the fragmentation table from the list.
* after this operation, the fragementation list will no longer
* hold a reference to this sender's fragmentation table
* @param sender - the sender who's fragmentation table you wish to remove, cannot be null
* @return true if the table was removed, false if the sender doesn't have an entry
*/
public boolean remove(Address sender) {
synchronized(frag_tables) {
boolean result=containsSender(sender);
frag_tables.remove(sender);
return result;
}
}
/**
* returns a list of all the senders that have fragmentation tables
* opened.
* @return an array of all the senders in the fragmentation list
*/
public Address[] getSenders() {
Address[] result;
int index=0;
synchronized(frag_tables) {
result=new Address[frag_tables.size()];
for(Iterator it=frag_tables.keySet().iterator(); it.hasNext();) {
result[index++]=(Address)it.next();
}
}
return result;
}
public String toString() {
Map.Entry entry;
StringBuffer buf=new StringBuffer("Fragmentation list contains ");
synchronized(frag_tables) {
buf.append(frag_tables.size()).append(" tables\n");
for(Iterator it=frag_tables.entrySet().iterator(); it.hasNext();) {
entry=(Map.Entry)it.next();
buf.append(entry.getKey()).append(": " ).append(entry.getValue()).append("\n");
}
}
return buf.toString();
}
}
/**
* Keeps track of the fragments that are received.
* Reassembles fragements into entire messages when all fragments have been received.
* The fragmentation holds a an array of byte arrays for a unique sender
* The first dimension of the array is the order of the fragmentation, in case the arrive out of order
*/
static class FragmentationTable {
private final Address sender;
/* the hashtable that holds the fragmentation entries for this sender*/
private final Hashtable h=new Hashtable(11); // keys: frag_ids, vals: Entrys
FragmentationTable(Address sender) {
this.sender=sender;
}
/**
* inner class represents an entry for a message
* each entry holds an array of byte arrays sorted
* once all the byte buffer entries have been filled
* the fragmentation is considered complete.
*/
static class Entry {
//the total number of fragment in this message
int tot_frags=0;
// each fragment is a byte buffer
Message fragments[]=null;
//the number of fragments we have received
int number_of_frags_recvd=0;
// the message ID
long msg_id=-1;
/**
* Creates a new entry
* @param tot_frags the number of fragments to expect for this message
*/
Entry(long msg_id, int tot_frags) {
this.msg_id=msg_id;
this.tot_frags=tot_frags;
fragments=new Message[tot_frags];
for(int i=0; i < tot_frags; i++)
fragments[i]=null;
}
/**
* adds on fragmentation buffer to the message
* @param frag_id the number of the fragment being added 0..(tot_num_of_frags - 1)
* @param frag the byte buffer containing the data for this fragmentation, should not be null
*/
public void set(int frag_id, Message frag) {
// don't count an already received fragment (should not happen though because the
// reliable transmission protocol(s) below should weed out duplicates
if(fragments[frag_id] == null) {
fragments[frag_id]=frag;
number_of_frags_recvd++;
}
}
/** returns true if this fragmentation is complete
* ie, all fragmentations have been received for this buffer
*
*/
public boolean isComplete() {
/*first make the simple check*/
if(number_of_frags_recvd < tot_frags) {
return false;
}
/*then double check just in case*/
for(int i=0; i < fragments.length; i++) {
if(fragments[i] == null)
return false;
}
/*all fragmentations have been received*/
return true;
}
/**
* Assembles all the fragments into one buffer. Takes all Messages, and combines their buffers into one
* buffer.
* This method does not check if the fragmentation is complete (use {@link #isComplete()} to verify
* before calling this method)
* @return the complete message in one buffer
*
*/
public Message assembleMessage() {
Message retval;
byte[] combined_buffer, tmp;
int combined_length=0, length, offset;
Message fragment;
int index=0;
for(int i=0; i < fragments.length; i++) {
fragment=fragments[i];
combined_length+=fragment.getLength();
}
combined_buffer=new byte[combined_length];
for(int i=0; i < fragments.length; i++) {
fragment=fragments[i];
tmp=fragment.getRawBuffer();
length=fragment.getLength();
offset=fragment.getOffset();
System.arraycopy(tmp, offset, combined_buffer, index, length);
index+=length;
}
retval=fragments[0].copy(false);
retval.setBuffer(combined_buffer);
return retval;
}
/**
* debug only
*/
public String toString() {
StringBuffer ret=new StringBuffer();
ret.append("[tot_frags=").append(tot_frags).append(", number_of_frags_recvd=").append(number_of_frags_recvd).append(']');
return ret.toString();
}
public int hashCode() {
return super.hashCode();
}
}
/**
* Creates a new entry if not yet present. Adds the fragment.
* If all fragements for a given message have been received,
* an entire message is reassembled and returned.
* Otherwise null is returned.
* @param id - the message ID, unique for a sender
* @param frag_id the index of this fragmentation (0..tot_frags-1)
* @param tot_frags the total number of fragmentations expected
* @param fragment - the byte buffer for this fragment
*/
public synchronized Message add(long id, int frag_id, int tot_frags, Message fragment) {
Message retval=null;
Entry e=(Entry)h.get(new Long(id));
if(e == null) { // Create new entry if not yet present
e=new Entry(id, tot_frags);
h.put(new Long(id), e);
}
e.set(frag_id, fragment);
if(e.isComplete()) {
retval=e.assembleMessage();
h.remove(new Long(id));
}
return retval;
}
public void reset() {
}
public String toString() {
StringBuffer buf=new StringBuffer("Fragmentation Table Sender:").append(sender).append("\n\t");
java.util.Enumeration e=this.h.elements();
while(e.hasMoreElements()) {
Entry entry=(Entry)e.nextElement();
int count=0;
for(int i=0; i < entry.fragments.length; i++) {
if(entry.fragments[i] != null) {
count++;
}
}
buf.append("Message ID:").append(entry.msg_id).append("\n\t");
buf.append("Total Frags:").append(entry.tot_frags).append("\n\t");
buf.append("Frags Received:").append(count).append("\n\n");
}
return buf.toString();
}
}
}