package org.jgroups.protocols;
import org.jgroups.*;
import org.jgroups.annotations.MBean;
import org.jgroups.annotations.ManagedAttribute;
import org.jgroups.annotations.Property;
import org.jgroups.stack.Protocol;
import org.jgroups.util.Average;
import org.jgroups.util.MessageBatch;
import java.io.DataInput;
import java.io.DataOutput;
/**
* Protocol measuring latency between stacks. On {@link Protocol#down(org.jgroups.Event)}, a header is added to the
* message with the ID of the PERF protocol and the start time is set in the header.
* On {@link Protocol#up(org.jgroups.Event)}, the time difference is computed and a rolling average is updated in PERF.<p/>
* Note that we can have several measurements by inserting PERF protocols with different IDs (Protocol.id) into the stack.</p>
* If PERF is used to measure latency between nodes running on different physical boxes, it is important that the clocks
* are synchronized, or else latency cannot be computed correctly (may even be negative).
* @author Bela Ban
* @since 3.5
*/
@MBean(description="Measures latency between PERF instances")
public class PERF extends Protocol {
protected Average avg;
protected Address local_addr;
@Property(description="Number of samples to maintain for rolling average")
protected int avg_size=20;
@ManagedAttribute(description="Average latency in ns")
public double latencyInNs() {return avg.getAverage();}
@ManagedAttribute(description="Average latency in ms")
public double latencyInMs() {return avg.getAverage() / 1000000.0;}
public void init() throws Exception {
super.init();
avg=new Average(avg_size);
}
public void resetStats() {
super.resetStats();
avg.clear();
}
public Object down(Event evt) {
switch(evt.getType()) {
case Event.MSG:
Message msg=(Message)evt.getArg();
msg.putHeader(id, new PerfHeader(System.nanoTime()));
break;
case Event.SET_LOCAL_ADDRESS:
local_addr=(Address)evt.getArg();
break;
}
return down_prot.down(evt);
}
public Object up(Event evt) {
if(evt.getType() == Event.MSG) {
Message msg=(Message)evt.getArg();
PerfHeader hdr=(PerfHeader)msg.getHeader(id);
if(hdr == null)
log.error("%s: no perf header found", local_addr);
else {
long time=System.nanoTime() - hdr.start_time;
if(time <= 0)
log.error("%s: time is <= 0");
else
avg.add(time);
}
}
return up_prot.up(evt);
}
public void up(MessageBatch batch) {
for(Message msg: batch) {
PerfHeader hdr=(PerfHeader)msg.getHeader(id);
if(hdr == null)
log.error("%s: no perf header found", local_addr);
else {
long time=System.nanoTime() - hdr.start_time;
if(time <= 0)
log.error("%s: time is <= 0");
else
avg.add(time);
}
}
super.up(batch);
}
protected static class PerfHeader extends Header {
protected long start_time; // in ns
public PerfHeader() {
}
public PerfHeader(long start_time) {
this.start_time=start_time;
}
public int size() {
return Global.LONG_SIZE;
}
public void writeTo(DataOutput out) throws Exception {
out.writeLong(start_time);
}
public void readFrom(DataInput in) throws Exception {
start_time=in.readLong();
}
}
}