FULL PRODUCT VERSION :
java version "1.6.0_11"
Java(TM) SE Runtime Environment (build 1.6.0_11-b03)
Java HotSpot(TM) 64-Bit Server VM (build 11.0-b16, mixed mode)

FULL OS VERSION :
Linux pixie 2.6.25-gentoo-r6 #4 SMP Fri Nov 14 15:47:41 CET 2008 x86_64 Dual Core AMD Opteron(tm) Processor 170 AuthenticAMD GNU/Linux

A DESCRIPTION OF THE PROBLEM :
As of JDK 1.6, lock are dispensed so that the thread current holding a lock is favored compared to other competing threads. This will cause other threads to starve.

  See also http://ceki.blogspot.com/2009/06/biased-locking-in-java-se-60.html

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Problem occurs anytime a resource protected by a synchronized block is accessed by multiple threads.


EXPECTED VERSUS ACTUAL BEHAVIOR :
Actual reaults
java.runtime.version = 1.6.0_11-b03
java.vendor = Sun Microsystems Inc.
java.version = 1.6.0_11
os.name = Linux
os.version = 2.6.25-gentoo-r6
runnable[0]: counter=1002
runnable[1]: counter=0
runnable[2]: counter=0
runnable[3]: counter=0
runnable[4]: counter=0

One would expect a more even distribution of the counter value.
REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
public class LockingInJava implements Runnable {

 static int THREAD_COUNT = 5;
 static Object LOCK = new Object();
 static Runnable[] RUNNABLE_ARRAY = new Runnable[THREAD_COUNT];
 static Thread[] THREAD_ARRAY = new Thread[THREAD_COUNT];

 private int counter = 0;

 public static void main(String args[]) throws InterruptedException {
   printEnvironmentInfo();
   execute();
   printResults();
 }

 public static void printEnvironmentInfo() {
   System.out.println("java.runtime.version = "
       + System.getProperty("java.runtime.version"));
   System.out.println("java.vendor = "
       + System.getProperty("java.vendor"));
   System.out.println("java.version = "
       + System.getProperty("java.version"));
   System.out.println("os.name = "
       + System.getProperty("os.name"));
   System.out.println("os.version = "
       + System.getProperty("os.version"));
 }

 public static void execute() throws InterruptedException {
    for (int i = 0; i < THREAD_COUNT; i++) {
      RUNNABLE_ARRAY[i] = new LockingInJava();
      THREAD_ARRAY[i] = new Thread(RUNNABLE_ARRAY[i]);
    }
    for (Thread t : THREAD_ARRAY) {
      t.start();
    }
    // let the threads run for a while
    Thread.sleep(10000);
    
    for (int i = THREAD_COUNT - 1; i <= 0; i--) {
      THREAD_ARRAY[i].interrupt();
    }
    Thread.sleep(100); // wait a moment for termination, to lazy for join ;)
  }

  public static void printResults() {
    for (int i = 0; i < RUNNABLE_ARRAY.length; i++) {
      System.out.println("runnable[" + i + "]: " + RUNNABLE_ARRAY[i]);
    }
  }

  public void run() {
    for (;;) {
      synchronized (LOCK) {
        counter++;
        try {
          Thread.sleep(10);
        } catch (InterruptedException ex) {
          break;
        }
      }
    }
  }

  public String toString() {
    return "counter=" + counter;
  }
}
---------- END SOURCE ----------