Singleton and Threading in EJB

[Scott Seo]

I have an application that I have been working on for the past year. It has mulple threads which may or may not open telnet session to a same ip address. I am using singleton as a central registry to block a tread from opening a telnet session to an ip address which may be in use by another telnet session spawned by another thread.
I am trying to port over some of the business logic to EJB. How would you address singleton and concurrency issues I have in EJB?

[Vijaykumar Dafal]

Hope you might find the below code snippet useful:
Note that you have to synchronize an object
public class Singleton
{
private static Singleton m_Singleton = null;
public static int i_Vallue=0;

private Singleton()
{
}
public Singleton getInstance()
{
synchronized(m_Singleton)
{
if(m_Singleton == null)
{
m_Singleton = new Singleton();
}
}
return m_Singleton;
}
public static void showValue()
{
System.out.println(i_Vallue++);
}
public static void main(String[] args)
{
new Singleton().showValue();
new Singleton().showValue();
new Singleton().showValue();
Singleton.showValue();
}
}
[ November 27, 2003: Message edited by: Vijaykumar Dafal ]

[Scott Seo]

Thanks for the snippet but when you have multiple JVMs such as mutiple EJB servers across mutilple servers, how can you synchrozied on an object?

[Kyle Brown]

Read this month's JavaRanch article on the Distributed Cache pattern.
Kyle