| java.lang.Object
 java.util.concurrent.atomic.AtomicReferenceFieldUpdater
| AtomicReferenceFieldUpdater | | abstract public class AtomicReferenceFieldUpdater (Code) | | 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 only with respect to other invocations of
compareAndSet and
set on the same updater.
since:
1.5
author:
Doug Lea<
Parameters:
T - > The type of the object holding the updatable field<
Parameters:
V - > The type of the field |
| Method Summary | |
| abstract public boolean | compareAndSet(T obj, V expect, V update)
Atomically sets the field of the given object managed by this updater
to the given updated value if the current value
== the
expected value. | | abstract public V | get(T obj)
Gets the current value held in the field of the given object managed
by this updater. | | public V | getAndSet(T obj, V newValue)
Atomically sets the field of the given object managed by this updater
to the given value and returns the old value. | | abstract public void | lazySet(T obj, V newValue)
Eventually sets the field of the given object managed by this
updater to the given updated value. | | public static 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.
Parameters:
vclass - the class of the field
Parameters:
fieldName - the name of the field to be updated. | | abstract public void | set(T obj, V newValue)
Sets the field of the given object managed by this updater to the
given updated value. | | abstract public boolean | weakCompareAndSet(T obj, V expect, V update)
Atomically sets the field of the given object managed by this updater
to the given updated value if the current value
== the
expected value. |
| AtomicReferenceFieldUpdater | | protected AtomicReferenceFieldUpdater()(Code) | | Protected do-nothing constructor for use by subclasses.
|
| compareAndSet | | abstract public boolean compareAndSet(T obj, V expect, V update)(Code) | | Atomically sets the field of the given object managed by this 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
Parameters:
expect - the expected value
Parameters:
update - the new value true if successful. |
| get | | abstract public V get(T obj)(Code) | | Gets the current value held in the field of the given object managed
by this updater.
Parameters:
obj - An object whose field to get the current value |
| getAndSet | | public V getAndSet(T obj, V newValue)(Code) | | Atomically sets the field of the given object managed by this updater
to the given value and returns the old value.
Parameters:
obj - An object whose field to get and set
Parameters:
newValue - the new value the previous value |
| lazySet | | abstract public void lazySet(T obj, V newValue)(Code) | | 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
Parameters:
newValue - the new value
since:
1.6 |
| newUpdater | | public static AtomicReferenceFieldUpdater<U, W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName)(Code) | | 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.
Parameters:
vclass - the class of the field
Parameters:
fieldName - the name of the field to be updated. the updater
throws:
IllegalArgumentException - if the field is not a volatile reference type.
throws:
RuntimeException - with a nested reflection-basedexception if the class does not hold field or is the wrong type. |
| set | | abstract public void set(T obj, V newValue)(Code) | | Sets the field of the given object managed by this updater to the
given updated value. 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
Parameters:
newValue - the new value |
| weakCompareAndSet | | abstract public boolean weakCompareAndSet(T obj, V expect, V update)(Code) | | Atomically sets the field of the given object managed by this 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.
May fail spuriously
and does not provide ordering guarantees, so is only rarely an
appropriate alternative to
compareAndSet .
Parameters:
obj - An object whose field to conditionally set
Parameters:
expect - the expected value
Parameters:
update - the new value true if successful. |
|
|