- /*
- * @(#)AtomicLongFieldUpdater.java 1.6 04/02/13
- *
- * Copyright 2004 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 <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> {
- private static final Unsafe unsafe = Unsafe.getUnsafe();
- 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> {
- private static final Unsafe unsafe = Unsafe.getUnsafe();
- 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);
- }
- }
- }
- }
-