package org.jgroups.protocols;
import org.jgroups.*;
import org.jgroups.annotations.Experimental;
import org.jgroups.annotations.MBean;
import org.jgroups.annotations.ManagedAttribute;
import org.jgroups.annotations.Property;
import org.jgroups.stack.Protocol;
import org.jgroups.util.Util;
import java.io.DataInput;
import java.io.DataOutput;
import java.util.concurrent.Executor;
/**
* Implementation of daisy chaining. Multicast messages are sent to our neighbor, which sends them to its neighbor etc.
* A TTL restricts the number of times a message is forwarded. The advantage of daisy chaining is that - for
* point-to-point transports such as TCP - we can avoid the N-1 issue: when A sends a multicast message to 10
* members, it needs to send it 9 times. With daisy chaining, it sends it 1 time, and in the next round, can already
* send another message. This leads to much better throughput, see the ref in the JIRA.<p/>
* Should be inserted just above MERGE2, in TCP based configurations.
* JIRA: https://jira.jboss.org/browse/JGRP-1021
* @author Bela Ban
* @since 2.11
*/
@Experimental
@MBean(description="Protocol just above the transport which disseminates multicasts via daisy chaining")
public class DAISYCHAIN extends Protocol {
/* ----------------------------------------- Properties -------------------------------------------------- */
@Property(description="Loop back multicast messages")
boolean loopback=true;
@Property(description="The number of messages in the forward queue. This queue is used to host messages that " +
"need to be forwarded by us on behalf of our neighbor",deprecatedMessage="not used anymore")
int forward_queue_size=10000;
@Property(description="The number of messages in the send queue. This queue is used to host messages that need " +
"to be sent",deprecatedMessage="not used anymore")
int send_queue_size=10000;
/* --------------------------------------------- Fields ------------------------------------------------------ */
protected volatile Address local_addr, next;
protected int view_size=0;
protected Executor default_pool=null;
protected Executor oob_pool=null;
protected volatile boolean running=true;
@ManagedAttribute
public int msgs_forwarded=0;
@ManagedAttribute
public int msgs_sent=0;
public void resetStats() {
super.resetStats();
msgs_forwarded=msgs_sent=0;
}
public void init() throws Exception {
default_pool=getTransport().getDefaultThreadPool();
oob_pool=getTransport().getOOBThreadPool();
}
public void start() throws Exception {
super.start();
running=true;
}
public void stop() {
super.stop();
running=false;
}
public Object down(final Event evt) {
switch(evt.getType()) {
case Event.MSG:
final Message msg=(Message)evt.getArg();
if(msg.getDest() != null)
break; // only process multicast messages
if(next == null) // view hasn't been received yet, use the normal transport
break;
// we need to copy the message, as we cannot do a msg.setSrc(next): the next retransmission
// would use 'next' as destination !
Message copy=msg.copy(true);
short hdr_ttl=(short)(loopback? view_size -1 : view_size);
DaisyHeader hdr=new DaisyHeader(hdr_ttl);
copy.setDest(next);
copy.putHeader(getId(), hdr);
msgs_sent++;
if(loopback) {
if(log.isTraceEnabled()) log.trace(new StringBuilder("looping back message ").append(msg));
if(msg.getSrc() == null)
msg.setSrc(local_addr);
Executor pool=msg.isFlagSet(Message.OOB)? oob_pool : default_pool;
pool.execute(new Runnable() {
public void run() {
up_prot.up(evt);
}
});
}
return down_prot.down(new Event(Event.MSG, copy));
case Event.VIEW_CHANGE:
handleView((View)evt.getArg());
break;
case Event.TMP_VIEW:
view_size=((View)evt.getArg()).size();
break;
case Event.SET_LOCAL_ADDRESS:
local_addr=(Address)evt.getArg();
break;
}
return down_prot.down(evt);
}
public Object up(Event evt) {
switch(evt.getType()) {
case Event.MSG:
Message msg=(Message)evt.getArg();
DaisyHeader hdr=(DaisyHeader)msg.getHeader(getId());
if(hdr == null)
break;
// 1. forward the message to the next in line if ttl > 0
short ttl=hdr.getTTL();
if(log.isTraceEnabled())
log.trace(local_addr + ": received message from " + msg.getSrc() + " with ttl=" + ttl);
if(--ttl > 0) {
Message copy=msg.copy(true);
copy.setDest(next);
copy.putHeader(getId(), new DaisyHeader(ttl));
msgs_forwarded++;
if(log.isTraceEnabled())
log.trace(local_addr + ": forwarding message to " + next + " with ttl=" + ttl);
down_prot.down(new Event(Event.MSG, copy));
}
// 2. Pass up
msg.setDest(null);
break;
}
return up_prot.up(evt);
}
protected void handleView(View view) {
view_size=view.size();
Address tmp=Util.pickNext(view.getMembers(), local_addr);
if(tmp != null && !tmp.equals(local_addr)) {
next=tmp;
if(log.isDebugEnabled())
log.debug("next=" + next);
}
}
public static class DaisyHeader extends Header {
private short ttl;
public DaisyHeader() {
}
public DaisyHeader(short ttl) {
this.ttl=ttl;
}
public short getTTL() {return ttl;}
public void setTTL(short ttl) {
this.ttl=ttl;
}
public int size() {
return Global.SHORT_SIZE;
}
public void writeTo(DataOutput out) throws Exception {
out.writeShort(ttl);
}
public void readFrom(DataInput in) throws Exception {
ttl=in.readShort();
}
public String toString() {
return "ttl=" + ttl;
}
}
}