/*
* @(#)AtomicLongFieldUpdater.java 1.14 06/06/15
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.util.concurrent.atomic;
import sun.misc.Unsafe;
import java.lang.reflect.*;
/**
* A reflection-based utility that enables atomic updates to
* designated {@code volatile long} fields of designated classes.
* This class is designed for use in atomic data structures in which
* several fields of the same node are independently subject to atomic
* updates.
*
* <p>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 <T> The type of the object holding the updatable field
*/
public abstract class AtomicLongFieldUpdater<T> {
/**
* Creates and returns an updater for objects with the given field.
* The Class argument is needed to check that reflective types and
* generic types match.
*
* @param tclass the class of the objects holding the field
* @param fieldName the name of the field to be updated.
* @return the updater
* @throws IllegalArgumentException if the field is not a
* volatile long type.
* @throws RuntimeException with a nested reflection-based
* exception if the class does not hold field or is the wrong type.
*/
public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
if (AtomicLong.VM_SUPPORTS_LONG_CAS)
return new CASUpdater<U>(tclass, fieldName);
else
return new LockedUpdater<U>(tclass, fieldName);
}
/**
* Protected do-nothing constructor for use by subclasses.
*/
protected AtomicLongFieldUpdater() {
}
/**
* 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.
* @throws ClassCastException if {@code obj} is not an instance
* of the class possessing the field established in the constructor.
*/
public abstract boolean compareAndSet(T obj, long expect, long 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.
*
* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
* 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.
* @throws ClassCastException if {@code obj} is not an instance
* of the class possessing the field established in the constructor.
*/
public abstract boolean weakCompareAndSet(T obj, long expect, long 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, long 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, long 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 long 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 long getAndSet(T obj, long newValue) {
for (;;) {
long current = get(obj);
if (compareAndSet(obj, current, newValue))
return current;
}
}
/**
* Atomically increments by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the previous value
*/
public long getAndIncrement(T obj) {
for (;;) {
long current = get(obj);
long next = current + 1;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically decrements by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the previous value
*/
public long getAndDecrement(T obj) {
for (;;) {
long current = get(obj);
long next = current - 1;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically adds the given value to the current value of the field of
* the given object managed by this updater.
*
* @param obj An object whose field to get and set
* @param delta the value to add
* @return the previous value
*/
public long getAndAdd(T obj, long delta) {
for (;;) {
long current = get(obj);
long next = current + delta;
if (compareAndSet(obj, current, next))
return current;
}
}
/**
* Atomically increments by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the updated value
*/
public long incrementAndGet(T obj) {
for (;;) {
long current = get(obj);
long next = current + 1;
if (compareAndSet(obj, current, next))
return next;
}
}
/**
* Atomically decrements by one the current value of the field of the
* given object managed by this updater.
*
* @param obj An object whose field to get and set
* @return the updated value
*/
public long decrementAndGet(T obj) {
for (;;) {
long current = get(obj);
long next = current - 1;
if (compareAndSet(obj, current, next))
return next;
}
}
/**
* Atomically adds the given value to the current value of the field of
* the given object managed by this updater.
*
* @param obj An object whose field to get and set
* @param delta the value to add
* @return the updated value
*/
public long addAndGet(T obj, long delta) {
for (;;) {
long current = get(obj);
long next = current + delta;
if (compareAndSet(obj, current, next))
return next;
}
}
private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
private static final Unsafe unsafe = Unsafe.getUnsafe();
private final long offset;
private final Class<T> tclass;
private final Class cclass;
CASUpdater(Class<T> tclass, String fieldName) {
Field field = null;
Class caller = null;
int modifiers = 0;
try {
field = tclass.getDeclaredField(fieldName);
caller = sun.reflect.Reflection.getCallerClass(3);
modifiers = field.getModifiers();
sun.reflect.misc.ReflectUtil.ensureMemberAccess(
caller, tclass, null, modifiers);
sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
} catch(Exception ex) {
throw new RuntimeException(ex);
}
Class fieldt = field.getType();
if (fieldt != long.class)
throw new IllegalArgumentException("Must be long type");
if (!Modifier.isVolatile(modifiers))
throw new IllegalArgumentException("Must be volatile type");
this.cclass = (Modifier.isProtected(modifiers) &&
caller != tclass) ? caller : null;
this.tclass = tclass;
offset = unsafe.objectFieldOffset(field);
}
private void fullCheck(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
if (cclass != null)
ensureProtectedAccess(obj);
}
public boolean compareAndSet(T obj, long expect, long update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.compareAndSwapLong(obj, offset, expect, update);
}
public boolean weakCompareAndSet(T obj, long expect, long update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.compareAndSwapLong(obj, offset, expect, update);
}
public void set(T obj, long newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
unsafe.putLongVolatile(obj, offset, newValue);
}
public void lazySet(T obj, long newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
unsafe.putOrderedLong(obj, offset, newValue);
}
public long get(T obj) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
return unsafe.getLongVolatile(obj, offset);
}
private void ensureProtectedAccess(T obj) {
if (cclass.isInstance(obj)) {
return;
}
throw new RuntimeException (
new IllegalAccessException("Class " +
cclass.getName() +
" can not access a protected member of class " +
tclass.getName() +
" using an instance of " +
obj.getClass().getName()
)
);
}
}
private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
private static final Unsafe unsafe = Unsafe.getUnsafe();
private final long offset;
private final Class<T> tclass;
private final Class cclass;
LockedUpdater(Class<T> tclass, String fieldName) {
Field field = null;
Class caller = null;
int modifiers = 0;
try {
field = tclass.getDeclaredField(fieldName);
caller = sun.reflect.Reflection.getCallerClass(3);
modifiers = field.getModifiers();
sun.reflect.misc.ReflectUtil.ensureMemberAccess(
caller, tclass, null, modifiers);
sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
} catch(Exception ex) {
throw new RuntimeException(ex);
}
Class fieldt = field.getType();
if (fieldt != long.class)
throw new IllegalArgumentException("Must be long type");
if (!Modifier.isVolatile(modifiers))
throw new IllegalArgumentException("Must be volatile type");
this.cclass = (Modifier.isProtected(modifiers) &&
caller != tclass) ? caller : null;
this.tclass = tclass;
offset = unsafe.objectFieldOffset(field);
}
private void fullCheck(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
if (cclass != null)
ensureProtectedAccess(obj);
}
public boolean compareAndSet(T obj, long expect, long update) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
synchronized(this) {
long v = unsafe.getLong(obj, offset);
if (v != expect)
return false;
unsafe.putLong(obj, offset, update);
return true;
}
}
public boolean weakCompareAndSet(T obj, long expect, long update) {
return compareAndSet(obj, expect, update);
}
public void set(T obj, long newValue) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
synchronized(this) {
unsafe.putLong(obj, offset, newValue);
}
}
public void lazySet(T obj, long newValue) {
set(obj, newValue);
}
public long get(T obj) {
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
synchronized(this) {
return unsafe.getLong(obj, offset);
}
}
private void ensureProtectedAccess(T obj) {
if (cclass.isInstance(obj)) {
return;
}
throw new RuntimeException (
new IllegalAccessException("Class " +
cclass.getName() +
" can not access a protected member of class " +
tclass.getName() +
" using an instance of " +
obj.getClass().getName()
)
);
}
}
}
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