org.apache.commons.lang3.concurrent
Class AtomicSafeInitializer<T>

java.lang.Object
  org.apache.commons.lang3.concurrent.AtomicSafeInitializer<T>

Type Parameters:

T - the type of the object managed by this initializer class

All Implemented Interfaces:

ConcurrentInitializer<T>

public abstract class AtomicSafeInitializer<T>
extends Object
implements ConcurrentInitializer<T>

A specialized ConcurrentInitializer implementation which is similar to AtomicInitializer, but ensures that the initialize() method is called only once.

As AtomicInitializer this class is based on atomic variables, so it can create an object under concurrent access without synchronization. However, it implements an additional check to guarantee that the initialize() method which actually creates the object cannot be called multiple times.

Because of this additional check this implementation is slightly less efficient than AtomicInitializer, but if the object creation in the initialize() method is expensive or if multiple invocations of initialize() are problematic, it is the better alternative.

From its semantics this class has the same properties as LazyInitializer. It is a "save" implementation of the lazy initializer pattern. Comparing both classes in terms of efficiency is difficult because which one is faster depends on multiple factors. Because AtomicSafeInitializer does not use synchronization at all it probably outruns LazyInitializer, at least under low or moderate concurrent access. Developers should run their own benchmarks on the expected target platform to decide which implementation is suitable for their specific use case.

Since:

3.0

Version:

$Id: AtomicSafeInitializer.java 1088899 2011-04-05 05:31:27Z bayard $

Constructor Summary

AtomicSafeInitializer()

Method Summary

T	get() Get (and initialize, if not initialized yet) the required object
protected abstract T	initialize() Creates and initializes the object managed by this AtomicInitializer.

Methods inherited from class java.lang.Object

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

Constructor Detail

AtomicSafeInitializer

public AtomicSafeInitializer()

Method Detail

get

public final T get()
            throws ConcurrentException

Get (and initialize, if not initialized yet) the required object

Specified by:

get in interface ConcurrentInitializer<T>

Returns:

lazily initialized object

Throws:

ConcurrentException - if the initialization of the object causes an exception

initialize

protected abstract T initialize()
                         throws ConcurrentException

Creates and initializes the object managed by this AtomicInitializer. This method is called by get() when the managed object is not available yet. An implementation can focus on the creation of the object. No synchronization is needed, as this is already handled by get(). This method is guaranteed to be called only once.

Returns:

the managed data object

Throws:

ConcurrentException - if an error occurs during object creation