com.atlassian.jira.util.concurrent
Class ThreadsafeLazyLoadedReference

java.lang.Object
  com.atlassian.jira.util.concurrent.ThreadsafeLazyLoadedReference

public abstract class ThreadsafeLazyLoadedReference
extends Object

Thread-safe lock-less (see note) reference that is not constructed until required. This class is used to maintain a reference to an object that is expensive to create and must be constructed once and once only. Therefore this reference behaves as though the final keyword has been used (you cannot reset it once it has been constructed).

When using this class you need to implement the create() method to return the object this reference will hold.

For instance:

  final ThreadsafeLazyLoadedReference ref = new ThreadsafeLazyLoadedReference()
  {
    protected Object create() throws Exception
    {
       // Do some useful object construction here
        return new MyObject();
    }
  };
 

Then call to get a reference to the object:

   MyObject myLazyLoadedObject = (MyObject) ref.get()
 

Note: uncomment generics declarations for Java 5 and change imports to java.util.concurrent.*

Note: The jdk1.4 backport of the util.concurrent libraries is actually not lockless as it uses synchronized to simulate the compareAndSet primitives in jdk1.5.

Nested Class Summary

static class

ThreadsafeLazyLoadedReference.InitializationException The factory create() method threw an exception.

Constructor Summary

ThreadsafeLazyLoadedReference()

Method Summary

protected abstract Object	create() The object factory method, guaranteed to be called once and only once.
Object	get() Get the lazily loaded reference.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ThreadsafeLazyLoadedReference

public ThreadsafeLazyLoadedReference()

Method Detail

get

public final Object get()

Get the lazily loaded reference. If your create() method throws an Exception, calls to get() will throw a RuntimeException which wraps the previously thrown exception.

create

protected abstract Object create()
                          throws Exception

The object factory method, guaranteed to be called once and only once.

protected abstract V create() throws Exception;

Throws:

Exception