Class AtomicInitializer<T>
- Type Parameters:
T
- the type of the object managed by this initializer class
- All Implemented Interfaces:
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:
- 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 theAtomicReference
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.
- Since:
- 3.0
-
Constructor Details
-
AtomicInitializer
public AtomicInitializer()
-
-
Method Details
-
get
Returns 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.- Specified by:
get
in interfaceConcurrentInitializer<T>
- Returns:
- the object created by this
AtomicInitializer
- Throws:
ConcurrentException
- if an error occurred during initialization of the object
-
initialize
Creates and initializes the object managed by thisAtomicInitializer
. This method is called byget()
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 byget()
. As stated by the class comment, it is possible that this method is called multiple times.- Returns:
- the managed data object
- Throws:
ConcurrentException
- if an error occurs during object creation
-