java.util.concurrent.atomic.AtomicReferenceFieldUpdater Maven / Gradle / Ivy
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* published by the Free Software Foundation. Oracle designates this
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* accompanied this code).
*
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/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package java.util.concurrent.atomic;
import java.lang.reflect.*;
import org.apidesign.bck2brwsr.core.JavaScriptBody;
/**
* A reflection-based utility that enables atomic updates to
* designated {@code 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
*
* {@code
* class Node {
* private volatile Node left, right;
*
* private static final AtomicReferenceFieldUpdater leftUpdater =
* AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
* private static AtomicReferenceFieldUpdater 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 {@code 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
* {@code compareAndSet} and {@code set} on the same updater.
*
* @since 1.5
* @author Doug Lea
* @param The type of the object holding the updatable field
* @param The type of the field
*/
public abstract class AtomicReferenceFieldUpdater {
/**
* 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.
*
* @param tclass the class of the objects holding the field.
* @param vclass the class of the field
* @param fieldName the name of the field to be updated.
* @return the updater
* @throws IllegalArgumentException if the field is not a volatile reference type.
* @throws RuntimeException with a nested reflection-based
* exception if the class does not hold field or is the wrong type.
*/
public static AtomicReferenceFieldUpdater newUpdater(Class tclass, Class vclass, String fieldName) {
return new Impl(tclass,
vclass,
fieldName);
}
/**
* Protected do-nothing constructor for use by subclasses.
*/
protected AtomicReferenceFieldUpdater() {
}
/**
* Atomically sets the field of the given object managed by this updater
* to the given updated value if the current value {@code ==} the
* expected value. This method is guaranteed to be atomic with respect to
* other calls to {@code compareAndSet} and {@code set}, but not
* necessarily with respect to other changes in the field.
*
* @param obj An object whose field to conditionally set
* @param expect the expected value
* @param update the new value
* @return true if successful.
*/
public abstract 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 {@code ==} the
* expected value. This method is guaranteed to be atomic with respect to
* other calls to {@code compareAndSet} and {@code 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 {@code compareAndSet}.
*
* @param obj An object whose field to conditionally set
* @param expect the expected value
* @param update the new value
* @return true if successful.
*/
public abstract boolean weakCompareAndSet(T obj, V expect, V update);
/**
* 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 {@code compareAndSet}.
*
* @param obj An object whose field to set
* @param newValue the new value
*/
public abstract void set(T obj, V newValue);
/**
* Eventually sets the field of the given object managed by this
* updater to the given updated value.
*
* @param obj An object whose field to set
* @param newValue the new value
* @since 1.6
*/
public abstract void lazySet(T obj, V newValue);
/**
* Gets the current value held in the field of the given object managed
* by this updater.
*
* @param obj An object whose field to get
* @return the current value
*/
public abstract V get(T obj);
/**
* Atomically sets the field of the given object managed by this updater
* to the given value and returns the old value.
*
* @param obj An object whose field to get and set
* @param newValue the new value
* @return the previous value
*/
public V getAndSet(T obj, V newValue) {
for (;;) {
V current = get(obj);
if (compareAndSet(obj, current, newValue))
return current;
}
}
/**
* Standard hotspot implementation using intrinsics
*/
private static class Impl extends AtomicReferenceFieldUpdater {
private final Object fn;
private Class tclass;
private Object cclass;
Impl(Class tclass, Class vclass, Object fieldName) {
if (!isFunction(fieldName)) {
throw new SecurityException("Updater can be used only from own class!");
}
this.tclass = tclass;
this.fn = fieldName;
}
@JavaScriptBody(args = { "obj", "fn" }, body = "return fn.call(obj);")
private static native Object get(Object obj, Object fn);
@JavaScriptBody(args = { "obj", "fn", "v" }, body = "fn.call(obj, v);")
private static native void set(Object obj, Object fn, Object v);
@JavaScriptBody(args = { "f" }, body = "return typeof f === 'function';")
private static native boolean isFunction(Object f);
private void fullCheck(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
}
@Override
public boolean compareAndSet(T obj, U expect, U update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
Object prev = get(obj, fn);
if (prev == expect) {
set(obj, fn, update);
return true;
}
return false;
}
@Override
public boolean weakCompareAndSet(T obj, U expect, U update) {
return compareAndSet(obj, expect, update);
}
@Override
public void set(T obj, U newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
set(obj, fn, newValue);
}
@Override
public void lazySet(T obj, U newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
set(obj, fn, newValue);
}
@Override
public final U get(T obj) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return (U) get(obj, fn);
}
}
}