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java.util.concurrent.atomic
Class AtomicReferenceFieldUpdater<T,V>
java.lang.Object
java.util.concurrent.atomic.AtomicReferenceFieldUpdater<T,V>
-
-
Type Parameters:
-
T - The type of the object holding the updatable field
-
V - The type of the field
-
public abstract class AtomicReferenceFieldUpdater<T,V>
- extends Object
A reflection-based utility that enables atomic updates to designated
volatile
reference fields of designated classes. This class is designed for use in atomic data structures in which several reference fields of the same node are independently subject to atomic updates. For example, a tree node might be declared as
class Node {
private volatile Node left, right;
private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
Node getLeft() { return left; }
boolean compareAndSetLeft(Node expect, Node update) {
return leftUpdater.compareAndSet(this, expect, update);
}
// ... and so on
}
Note that the guarantees of the
compareAndSet
method in this class are weaker than in other atomic classes. Because this class cannot ensure that all uses of the field are appropriate for purposes of atomic access, it can guarantee atomicity
and volatile semantics
only with respect to other invocations of
compareAndSet
and
set
on the same updater.
.
-
Since:
-
1.5
Method Summary
|
abstract boolean |
compareAndSet
(
T
obj,
V
expect,
V
Atomically
sets
set
the
value of the
field of the given object managed by this
updater
Updater
to the given updated value if the current value
==
the expected value. |
abstract
V
|
get
(
T
Gets
Get
the current value held in the field
of
by
the given
object managed by this updater.
object.
|
V
|
getAndSet
(
T
obj,
V
Atomically sets the field of the given object managed by this updater
Set
to the given value and
returns
return
the old value. |
abstract void
|
lazySet
(
T
obj,
V
Eventually sets the field of the given object managed by this updater to the given updated value.
|
static
|
newUpdater
(
Class
<U> tclass,
Class
<W> vclass,
String
fieldName)
Creates
and returns
an updater for objects with the given field. |
abstract void |
set
(
T
obj,
V
Sets
Set
the field of the given object managed by this
updater to the given updated value.
updater.
|
abstract boolean |
weakCompareAndSet
(
T
obj,
V
expect,
V
Atomically
sets
set
the
value of the
field of the given object managed by this
updater
Updater
to the given updated value if the current value
==
the expected value. |
Methods inherited from class java.lang.
Object
|
clone
,
equals
,
finalize
,
getClass
,
hashCode
,
notify
,
notifyAll
,
toString
,
wait
,
wait
,
wait
|
AtomicReferenceFieldUpdater
protected AtomicReferenceFieldUpdater()
-
Protected do-nothing constructor for use by subclasses.
newUpdater
public static <U,W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass,
Class<W> vclass,
String fieldName)
-
Creates
and returns
an updater for objects with the given field. The Class arguments are needed to check that reflective types and generic types match.
-
-
Parameters:
-
tclass - the class of the objects holding the field.
-
vclass - the class of the field
-
fieldName - the name of the field to be updated.
-
Returns:
-
the updater
-
Throws:
-
IllegalArgumentException
- if the field is not a volatile reference type.
-
RuntimeException
- with a nested reflection-based exception if the class does not hold field or is the wrong type.
compareAndSet
public abstract boolean compareAndSet(T obj,
V expect,
V update)
-
Atomically
sets
set
the
value of the
field of the given object managed by this
updater
Updater
to the given updated value if the current value
==
the expected value. This method is guaranteed to be atomic with respect to other calls to
compareAndSet
and
set
, but not necessarily with respect to other changes in the field.
-
-
Parameters:
-
obj - An object whose field to conditionally set
-
expect - the expected value
-
update - the new value
-
Returns:
-
true if successful.
weakCompareAndSet
public abstract boolean weakCompareAndSet(T obj,
V expect,
V update)
-
Atomically
sets
set
the
value of the
field of the given object managed by this
updater
Updater
to the given updated value if the current value
==
the expected value. This method is guaranteed to be atomic with respect to other calls to
compareAndSet
and
set
, but not necessarily with respect to other changes in the field, and may fail spuriously.
-
-
Parameters:
-
obj - An object whose field to conditionally set
-
expect - the expected value
-
update - the new value
-
Returns:
-
true if successful.
set
public abstract void set(T obj,
V newValue)
-
Sets
Set
the field of the given object managed by this
updater to the given updated value.
updater.
This operation is guaranteed to act as a volatile store with respect to subsequent invocations of
compareAndSet
.
-
-
Parameters:
-
obj - An object whose field to set
-
newValue - the new value
lazySet
public abstract void
lazySet
(
T
obj,
V
newValue)
-
Eventually sets the field of the given object managed by this updater to the given updated value.
-
-
Parameters:
-
obj - An object whose field to set
-
newValue - the new value
-
Since:
-
1.6
get
public abstract V get(T obj)
-
Gets
Get
the current value held in the field
of
by
the given
object managed by this updater.
object.
-
-
Parameters:
-
obj - An object whose field to get
-
Returns:
-
the current value
getAndSet
public V getAndSet(T obj,
V newValue)
-
Atomically sets the field of the given object managed by this updater
Set
to the given value and
returns
return
the old value.
-
-
Parameters:
-
obj - An object whose field to get and set
-
newValue - the new value
-
Returns:
-
the previous value