FULL PRODUCT VERSION :
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Client VM (build 1.6.0_01-b06, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Linux localhost 2.6.21-1.3194.fc7 #1 SMP Wed May 23 22:35:01 EDT 2007 i686 i686 i386 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
Properties.equal deadlocks if two threads simultaneously call equals between two Properties objects.

The javadoc for Properties states that this class is thread-safe:
http://java.sun.com/javase/6/docs/api/java/util/Properties.html


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Run example code.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Sample code run indefinitely.
ACTUAL -
  Program exits and prints:
 
   java.util.Hashtable.get(Hashtable.java:333)
    java.util.Hashtable.equals(Hashtable.java:755)
    PropertyBagDeadlock$1.run(PropertyBagDeadlock.java:31)

    java.util.Hashtable.size(Hashtable.java:206)
    java.util.Hashtable.equals(Hashtable.java:742)
    PropertyBagDeadlock$2.run(PropertyBagDeadlock.java:44)


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.lang.management.ManagementFactory;
import java.lang.management.ThreadMXBean;
import java.util.Properties;


public class PropertyBagDeadlock
{
   public static void main(String[] args)
   {
      final Properties p1 = new Properties();
      p1.put("1", new Object());
      p1.put("2", new Object());
      p1.put("3", new Object());
      
      final Properties p2 = new Properties();
      p2.put("1", new Object());
      p2.put("2", new Object());
      p2.put("3", new Object());
      
      Thread t1 = new Thread()
      {
         @Override
         public void run()
         {
            while(true)
            {
               p1.equals(p2);
            }
         }
      };
      t1.start();
      
      Thread t2 = new Thread()
      {
         @Override
         public void run()
         {
            while(true)
            {
               p2.equals(p1);
            }
         }
      };
      t2.start();
      
      while(true)
      {
         try
         {
            Thread.sleep(1000);
            ThreadMXBean manager = ManagementFactory.getThreadMXBean();
            long[] deadlockedThreads = manager.findMonitorDeadlockedThreads();
            if (deadlockedThreads != null && deadlockedThreads.length > 0)
            {
               printStack(t1);
               printStack(t2);
               System.exit(0);
            }
         }
         catch (InterruptedException e)
         {
         }
      }
   }
   
   private static void printStack(Thread t)
   {
      StringBuilder buf = new StringBuilder();
      StackTraceElement[] stack = t.getStackTrace();
      for(int j = 0; j < stack.length; j++)
      {
         buf.append(" ");
         buf.append(stack[j].toString());
         buf.append("\n");
      }
      System.err.println(buf);
   }
---------- END SOURCE ----------