Re: synchronized block improving performance

Hi,

I was getting a ConcurrentModificationException with some of the
accessor methods on a class so I fixed it by synchronizing all methods
that iterated over the underlying java.util.Vector object. The CME
has gone away but also the performance has improved which seems
counter-intuitive.

I created a SynchronizedSpeedTest that just iterates through a vector
of objects and this confirmed my suspicion that the code that includes
the synchronized blocks should run slower. Can anyone think of any
reason why it might actually run quicker?

import java.util.Iterator;
import java.util.Vector;

import junit.framework.TestCase;

public class SynchronizedSpeedTest extends TestCase {

        Vector oTestData;

        public void setUp() {
                oTestData = new Vector();
                for (int i=0; i<1000; i++) {
                        oTestData.add(new Integer(i));
                }
                System.out.println("Done setting up...");
        }

        private void iterateSynchronized() {
                synchronized(oTestData) {
                        Iterator iter = oTestData.iterator();
                        while(iter.hasNext()) { iter.next(); }
                }
        }

        private void iterateUnsynchronized() {
                Iterator iter = oTestData.iterator();
                while(iter.hasNext()) { iter.next(); }
        }

        public void testSynchronized() {
                long nStart = System.currentTimeMillis();
                long nEnd = nStart + (1000 * 10);

                int nCount = 0;
                while(System.currentTimeMillis() < nEnd) {
                        iterateSynchronized();
                        nCount++;
                }
                System.out.println("" + nCount + " synchronized iterations");
        }

        public void testUnsynchronized() {
                long nStart = System.currentTimeMillis();
                long nEnd = nStart + (1000 * 10);

                int nCount = 0;
                while(System.currentTimeMillis() <= nEnd) {
                        iterateUnsynchronized();
                        nCount++;
                }
                System.out.println("" + nCount + " unsynchronized iterations");
        }

}