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AtomicInitializer

public class org.apache.commons.lang3.concurrent.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 #initialize() method is called. This method must be defined in concrete subclasses to actually create the managed object.

• After the object was created by #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 #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 #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.

Parameters:

<T> – The type of the object managed by this initializer class.

Since:

3.0

Constructors

AtomicInitializer()

Constructs a new instance.

public AtomicInitializer()

Constructs a new instance.

Methods

builder()	Creates a new builder.
get()	Gets the object managed by this initializer.
getTypedException(Exception)	Gets an Exception with a type of E as defined by a concrete subclass of this class.
isInitialized()	Tests whether this instance is initialized.

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

@Override 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:

org.apache.commons.lang3.concurrent.ConcurrentException – Thrown if an error occurred during initialization of the object.

@Override protected ConcurrentException getTypedException(Exception e)

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

Parameters:

e – The actual exception that was thrown.

Returns:

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

@Override public boolean isInitialized()

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

Returns:

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

Since:

3.14.0