Threads not getting expected speedup

I'm trying to write some code which will split up a vector into two
halves and run a method on the objects in the vector using two seperate
threads. I was hoping to see a near linear speedup on an SMP machine,
but I'm finding that the code below takes almost exactly the same
amount of time as when I iterate through the vector, and don't use any
threads at all (using only one processor). I'm running this on a Dual
Athlon machine under Redhat 9, and when I look at the processors,
they're both maxed out. Thanks in advance for any help.

andy

SMPEvlautionWra pper processor1Threa d; // This Class extends
Thread
SMPEvlautionWra pper processor2Threa d; // and holds some other
vars.

Vector tempEvalPopulat ion1=new Vector();
Vector tempEvalPopulat ion2=new Vector();
for (int j=0;j<tempRetur nVector.size()/2;j++){

tempEvalPopulat ion1.add((Indiv idual)tempRetur nVector.element At(j));
}
for (int
j=tempReturnVec tor.size()/2;j<tempReturnV ector.size();j+ +){

tempEvalPopulat ion2.add((Indiv idual)tempRetur nVector.element At(j));
}
It might be better to use the List.subList() to split the Vectors.

processor1Threa d= new SMPEvlautionWra pper();
processor2Threa d= new SMPEvlautionWra pper();

processor1Threa d.initVars("pro cessor
1",(Vector)temp EvalPopulation1 .clone(),(Evalu ationFunction)t empEval.copy()) ;
processor2Threa d.initVars("pro cessor
2",(Vector)temp EvalPopulation2 .clone(),(Evalu ationFunction)t empEval.copy()) ;
try{
processor1Threa d.start();
processor2Threa d.start();
}catch(Exceptio n ex){
ex.printStackTr ace();
}

while(true){
if
((processor1Thr ead.finished==t rue)&&(processo r2Thread.finish ed==true)){
break;
}
try{
Thread.sleep(10 );
}catch(Exceptio n ex){
ex.printStackTr ace();
}

}

Thread
SMPEvlautionWra pper processor2Threa d; // and holds some other

processor1Threa d= new SMPEvlautionWra pper();
processor2Threa d= new SMPEvlautionWra pper();

try{
processor1Threa d.start();
processor2Threa d.start();
}catch(Exceptio n ex){
ex.printStackTr ace();
}

while(true){
if
((processor1Thr ead.finished==t rue)&&(processo r2Thread.finish ed==true)){ break;
}
try{
Thread.sleep(10 );
}catch(Exceptio n ex){
ex.printStackTr ace();
}

}

This loop at the end here is probably a problem. What you really

need to do here is use Object.wait() and Object.notify() to synchronize your threads. That would get rid of the polling.

HTH,
Ray

--
XML is the programmer's duct tape.

SMPEvlautionWra pper processor1Threa d; // This Class extends
Thread
SMPEvlautionWra pper processor2Threa d; // and holds some other

processor1Threa d= new SMPEvlautionWra pper();
processor2Threa d= new SMPEvlautionWra pper();

try{
processor1Threa d.start();
processor2Threa d.start();
}catch(Exceptio n ex){
ex.printStackTr ace();
}

while(true){
if

((processor1Thr ead.finished==t rue)&&(processo r2Thread.finish ed==true)){
break;
}
try{
Thread.sleep(10 );
}catch(Exceptio n ex){
ex.printStackTr ace();
}

}

This loop at the end here is probably a problem. What you really

need

to do here is use Object.wait() and Object.notify() to synchronize

your

threads. That would get rid of the polling.

HTH,
Ray

--
XML is the programmer's duct tape.

Thanks alot for the help. I'm pretty new working with threads outside
of the simplest contexts. I tried substituting wait() on a dummy
variable for sleep() in the loop, and did get the speedup that I was
hoping for, i know this is the wrong way to be going about it (I get an
IllegalMonitorE xception). Can you suggest which object i should be
waiting on and which should be notifying? It also seems like if I
synchronize the entire method, both threads will operate on a single
processor. I'm having a hard time finding any good explinations in the
web literature.
Thanks.

an***********@h otmail.com wrote:

SMPEvlautionWra pper processor1Threa d; // This Class extends
Thread
SMPEvlautionWra pper processor2Threa d; // and holds some other
processor1Threa d= new SMPEvlautionWra pper();
processor2Threa d= new SMPEvlautionWra pper();

try{
processor1Threa d.start();
processor2Threa d.start();
}catch(Exceptio n ex){
ex.printStackTr ace();
}

while(true){
if

((processor1Thr ead.finished==t rue)&&(processo r2Thread.finish ed==true)){

break;
}
try{
Thread.sleep(10 );
}catch(Exceptio n ex){
ex.printStackTr ace();
}

}
This loop at the end here is probably a problem. What you really

need

to do here is use Object.wait() and Object.notify() to synchronize

your

threads. That would get rid of the polling.

HTH,
Ray

--
XML is the programmer's duct tape.

Thanks alot for the help. I'm pretty new working with threads outside of the simplest contexts. I tried substituting wait() on a dummy
variable for sleep() in the loop, and did get the speedup that I was hoping for, i know this is the wrong way to be going about it (I get an IllegalMonitorE xception). Can you suggest which object i should be
waiting on and which should be notifying? It also seems like if I
synchronize the entire method, both threads will operate on a single processor. I'm having a hard time finding any good explinations in the web literature.
Thanks.

I'd suggest that you make a new object for each thread. Make sure

you read the javadoc for Object.wait() and Object.notify() carefully.

The code might look something like this:

// Thread code
public void run()
{
// Do work
// ...

synchronized (sem)
{
sem.notifyAll() ;
}
}

// In the original thread
Object sem1 = new Object();
Object sem2 = new Object();
processor1Threa d.setSem(sem1);
processor2Threa d.setSem(sem2);
processor1Threa d.start();
processor2Threa d.start();

synchronized (sem1)
{
if (!processor1Thr ead.finished)
{
sem1.wait();
}
}

synchronized (sem2)
{
if (!processor2Thr ead.finished)
{
sem2.wait();
}
}

HTH,
Ray

--
XML is the programmer's duct tape.