Name: mc57594 Date: 03/06/97


IMPORTANT:
this code works with jdk 1.0.2
but it fails with jdk 1.1

// FILE Singleton.java

public class Singleton {
protected static Singleton _Single = null;
protected String _Value = "default";

static {
GetSingleton();
}

public static Singleton GetSingleton() {
   if (_Single == null) {
      _Single = new Singleton();
   }
   return(_Single);
}

protected Singleton()
{
System.err.println("creating");
}

public void Set(String s)
{
   _Value = s;
}

public String toString()
{
   return _Value;
}

protected void finalize() throws Throwable
{
System.err.println("finalizing");
}
}



// FILE TestSingle.java

import java.lang.*;

class TestSingle extends Thread {
public TestSingle()
{
}

public void run()
{
Thread t = Thread.currentThread();
   try {
t.sleep(20000);
   }
   catch(Exception es) {}
}

public static void main(String[] args)
{
TestSingle t1;

try {
   Class c = Class.forName("Singleton");
   t1 = new TestSingle();
   t1.start();
   t1.join();
   t1.stop();
}catch(Exception e){
System.err.println(e);
}
}
}

running the command :
java TestSingle
the output is:
creating
finalizing

the finalize() method is called about 1 second after
the creation of the singleton, while the test thread is
still running
company - Elasis s.c.p.A. , email - ###@###.###
======================================================================

[sheri.good@Eng 1997-03-26]
This looks like the same bug. If it isn't, I can submit as a separate bug.


Category: java
Subcategory: runtime
Bug/rfe/eou: comment
Synopsis: Classes with a static reference to self, and no other references get garbage collected
Severity Impact: (internal)
Severity Functionality: (internal)
Priority: (internal)
Description: Access to the an instance of the class below is through its
getInstance method so there are no references to the class
to tell the gc not to collect it.

public class Singleton {
 private static Singleton instance = null;
 public static Singleton getInstance () {
  if (instance == null) instance = new Singleton()
  return instance;
 }
 private Singleton () { }
 public void methodX() {}
 public void methodY() {}
 public void methodZ() {}
}


  
company - WorldStreet Corporation , email - ###@###.###
Work around: Create a singleton registry class which has a reference to all
singleton objects. Then you only have to keep a reference
around for the registry. Alternatively, a public noGC flag
could be added to Class which the runtime could check before
gc'ing the class.
Comments:
customer_rec: new
Company: other
Employee:Edward Shea
Release: jdk11
Hardware Version: i586
O/S version: win_nt_4.0
User Role: D
User Type: E
Sun Contact: (internal)
end_customer_rec:
BUG_END