/*
* 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/licenses/publicdomain
*/
package java.util.concurrent.atomic;
import sun.misc.Unsafe;
import java.lang.reflect.*;
/**
* A reflection-based utility that enables atomic updates to
* designated <tt>volatile long</tt> 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 <tt>compareAndSet</tt> 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
* <tt>compareAndSet</tt> and <tt>set</tt>.
*
* @since 1.5
* @author Doug Lea
* @param <T> The type of the object holding the updatable field
*/
public abstract class AtomicLongFieldUpdater<T> {
/**
* Creates 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 set the value of the field of the given object managed
* by this Updater to the given updated value if the current value
* <tt>==</tt> the expected value. This method is guaranteed to be
* atomic with respect to other calls to <tt>compareAndSet</tt> and
* <tt>set</tt>, 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 <tt>obj</tt> 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 set the value of the field of the given object managed
* by this Updater to the given updated value if the current value
* <tt>==</tt> the expected value. This method is guaranteed to be
* atomic with respect to other calls to <tt>compareAndSet</tt> and
* <tt>set</tt>, but not necessarily with respect to other
* changes in the field, and may fail spuriously.
* @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 <tt>obj</tt> is not an instance
* of the class possessing the field established in the constructor.
*/
public abstract boolean weakCompareAndSet(T obj, long expect, long update);
/**
* Set the field of the given object managed by this updater. This
* operation is guaranteed to act as a volatile store with respect
* to subsequent invocations of <tt>compareAndSet</tt>.
* @param obj An object whose field to set
* @param newValue the new value
*/
public abstract void set(T obj, long newValue);
/**
* Get the current value held in the field by the given object.
* @param obj An object whose field to get
* @return the current value
*/
public abstract long get(T obj);
/**
* Set to the given value and return 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 increment by one the current value.
* @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 decrement by one the current value.
* @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 add the given value to current value.
* @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 increment by one the current value.
* @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 decrement by one the current value.
* @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 add the given value to current value.
* @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> {
// BEGIN android-changed
private static final Unsafe unsafe = UnsafeAccess.THE_ONE;
// END android-changed
private final long offset;
private final Class<T> tclass;
CASUpdater(Class<T> tclass, String fieldName) {
Field field = null;
try {
field = tclass.getDeclaredField(fieldName);
} 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(field.getModifiers()))
throw new IllegalArgumentException("Must be volatile type");
this.tclass = tclass;
offset = unsafe.objectFieldOffset(field);
}
public boolean compareAndSet(T obj, long expect, long update) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
return unsafe.compareAndSwapLong(obj, offset, expect, update);
}
public boolean weakCompareAndSet(T obj, long expect, long update) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
return unsafe.compareAndSwapLong(obj, offset, expect, update);
}
public void set(T obj, long newValue) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
unsafe.putLongVolatile(obj, offset, newValue);
}
public long get(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
return unsafe.getLongVolatile(obj, offset);
}
}
private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
// BEGIN android-changed
private static final Unsafe unsafe = UnsafeAccess.THE_ONE;
// END android-changed
private final long offset;
private final Class<T> tclass;
LockedUpdater(Class<T> tclass, String fieldName) {
Field field = null;
try {
field = tclass.getDeclaredField(fieldName);
} 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(field.getModifiers()))
throw new IllegalArgumentException("Must be volatile type");
this.tclass = tclass;
offset = unsafe.objectFieldOffset(field);
}
public boolean compareAndSet(T obj, long expect, long update) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
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 (!tclass.isInstance(obj))
throw new ClassCastException();
synchronized(this) {
unsafe.putLong(obj, offset, newValue);
}
}
public long get(T obj) {
if (!tclass.isInstance(obj))
throw new ClassCastException();
synchronized(this) {
return unsafe.getLong(obj, offset);
}
}
}
}
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