org.apache.commons.lang3.concurrent

Class AtomicInitializer<T>

java.lang.Object

org.apache.commons.lang3.concurrent.AbstractConcurrentInitializer<T,ConcurrentException>

org.apache.commons.lang3.concurrent.AtomicInitializer<T>

Type Parameters:

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

All Implemented Interfaces:

ConcurrentInitializer<T>, FailableSupplier<T,ConcurrentException>

public class AtomicInitializer<T>
extends AbstractConcurrentInitializer<T,ConcurrentException>

A specialized implementation of the ConcurrentInitializer interface based on an AtomicReference variable.

This class maintains a member field of type AtomicReference. It implements the following algorithm to create and initialize an object in its get() method:

• First it is checked whether the AtomicReference variable contains already a value. If this is the case, the value is directly returned.
• Otherwise the AbstractConcurrentInitializer.initialize() method is called. This method must be defined in concrete subclasses to actually create the managed object.
• After the object was created by AbstractConcurrentInitializer.initialize() it is checked whether the AtomicReference variable is still undefined. This has to be done because in the meantime another thread may have initialized the object. If the reference is still empty, the newly created object is stored in it and returned by this method.
• Otherwise the value stored in the AtomicReference is returned.

Because atomic variables are used this class does not need any synchronization. So there is no danger of deadlock, and access to the managed object is efficient. However, if multiple threads access the AtomicInitializer object before it has been initialized almost at the same time, it can happen that AbstractConcurrentInitializer.initialize() is called multiple times. The algorithm outlined above guarantees that get() always returns the same object though.

Compared with the LazyInitializer class, this class can be more efficient because it does not need synchronization. The drawback is that the AbstractConcurrentInitializer.initialize() method can be called multiple times which may be problematic if the creation of the managed object is expensive. As a rule of thumb this initializer implementation is preferable if there are not too many threads involved and the probability that multiple threads access an uninitialized object is small. If there is high parallelism, LazyInitializer is more appropriate.

Since:

3.0

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	AtomicInitializer.Builder<I extends AtomicInitializer<T>,T> Builds a new instance.

Nested classes/interfaces inherited from class org.apache.commons.lang3.concurrent.AbstractConcurrentInitializer

AbstractConcurrentInitializer.AbstractBuilder<I extends AbstractConcurrentInitializer<T,E>,T,B extends AbstractConcurrentInitializer.AbstractBuilder<I,T,B,E>,E extends Exception>

Field Summary

Fields inherited from interface org.apache.commons.lang3.function.FailableSupplier

NUL

Constructor Summary

Constructors

Constructor and Description
AtomicInitializer() Constructs a new instance.

Method Summary

Modifier and Type	Method and Description
static <T> AtomicInitializer.Builder<AtomicInitializer<T>,T>	builder() Creates a new builder.
T	get() Gets the object managed by this initializer.
protected ConcurrentException	getTypedException(Exception e) Gets an Exception with a type of E as defined by a concrete subclass of this class.
boolean	isInitialized() Tests whether this instance is initialized.

Methods inherited from class org.apache.commons.lang3.concurrent.AbstractConcurrentInitializer

close, initialize

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.commons.lang3.function.FailableSupplier

nul

Constructor Detail

AtomicInitializer

public AtomicInitializer()

Constructs a new instance.

Method Detail

builder

public static <T> AtomicInitializer.Builder<AtomicInitializer<T>,T> builder()

Creates a new builder.

Type Parameters:

T - the type of object to build.

Returns:

a new builder.

Since:

3.14.0

get

public T get()
      throws ConcurrentException

Gets the object managed by this initializer. The object is created if it is not available yet and stored internally. This method always returns the same object.

Returns:

the object created by this AtomicInitializer

Throws:

ConcurrentException - if an error occurred during initialization of the object

getTypedException

protected ConcurrentException getTypedException(Exception e)

Gets an Exception with a type of E as defined by a concrete subclass of this class.

Specified by:

getTypedException in class AbstractConcurrentInitializer<T,ConcurrentException>

Parameters:

e - The actual exception that was thrown

Returns:

a new exception with the actual type of E, that wraps e.

isInitialized

public boolean isInitialized()

Tests whether this instance is initialized. Once initialized, always returns true.

Specified by:

isInitialized in class AbstractConcurrentInitializer<T,ConcurrentException>

Returns:

whether this instance is initialized. Once initialized, always returns true.

Since:

3.14.0