T
- the type of the object managed by this initializer classpublic abstract class AtomicInitializer<T> extends java.lang.Object implements ConcurrentInitializer<T>
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:
AtomicReference
variable contains
already a value. If this is the case, the value is directly returned.initialize()
method is called. This method must be
defined in concrete subclasses to actually create the managed object.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.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.
Constructor and Description |
---|
AtomicInitializer() |
Modifier and Type | Method and Description |
---|---|
T |
get()
Returns the object managed by this initializer.
|
public T get() throws ConcurrentException
get
in interface ConcurrentInitializer<T>
AtomicInitializer
ConcurrentException
- if an error occurred during initialization of
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