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jeremybenn |
/*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/licenses/publicdomain
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*/
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package java.util.concurrent.atomic;
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import sun.misc.Unsafe;
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import java.lang.reflect.*;
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/**
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* A reflection-based utility that enables atomic updates to
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* designated <tt>volatile long</tt> fields of designated classes.
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* This class is designed for use in atomic data structures in which
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* several fields of the same node are independently subject to atomic
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* updates.
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*
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* <p>Note that the guarantees of the {@code compareAndSet}
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* method in this class are weaker than in other atomic classes.
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* Because this class cannot ensure that all uses of the field
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* are appropriate for purposes of atomic access, it can
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* guarantee atomicity only with respect to other invocations of
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* {@code compareAndSet} and {@code set} on the same updater.
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*
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* @since 1.5
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* @author Doug Lea
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* @param <T> The type of the object holding the updatable field
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*/
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public abstract class AtomicLongFieldUpdater<T> {
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/**
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* Creates and returns an updater for objects with the given field.
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* The Class argument is needed to check that reflective types and
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* generic types match.
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*
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* @param tclass the class of the objects holding the field
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* @param fieldName the name of the field to be updated.
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* @return the updater
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* @throws IllegalArgumentException if the field is not a
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* volatile long type.
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* @throws RuntimeException with a nested reflection-based
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* exception if the class does not hold field or is the wrong type.
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*/
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public static <U> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
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if (AtomicLong.VM_SUPPORTS_LONG_CAS)
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return new CASUpdater<U>(tclass, fieldName);
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else
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return new LockedUpdater<U>(tclass, fieldName);
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}
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/**
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* Protected do-nothing constructor for use by subclasses.
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*/
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protected AtomicLongFieldUpdater() {
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}
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given updated value if the current value <tt>==</tt> the
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* expected value. This method is guaranteed to be atomic with respect to
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* other calls to <tt>compareAndSet</tt> and <tt>set</tt>, but not
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* necessarily with respect to other changes in the field.
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*
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* @param obj An object whose field to conditionally set
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* @param expect the expected value
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* @param update the new value
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* @return true if successful.
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* @throws ClassCastException if <tt>obj</tt> is not an instance
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* of the class possessing the field established in the constructor.
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*/
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public abstract boolean compareAndSet(T obj, long expect, long update);
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given updated value if the current value <tt>==</tt> the
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* expected value. This method is guaranteed to be atomic with respect to
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* other calls to <tt>compareAndSet</tt> and <tt>set</tt>, but not
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* necessarily with respect to other changes in the field.
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* May fail spuriously and does not provide ordering guarantees,
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* so is only rarely an appropriate alternative to <tt>compareAndSet</tt>.
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*
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* @param obj An object whose field to conditionally set
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* @param expect the expected value
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* @param update the new value
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* @return true if successful.
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* @throws ClassCastException if <tt>obj</tt> is not an instance
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* of the class possessing the field established in the constructor.
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*/
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public abstract boolean weakCompareAndSet(T obj, long expect, long update);
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/**
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* Sets the field of the given object managed by this updater to the
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* given updated value. This operation is guaranteed to act as a volatile
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* store with respect to subsequent invocations of
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* <tt>compareAndSet</tt>.
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*
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* @param obj An object whose field to set
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* @param newValue the new value
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*/
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public abstract void set(T obj, long newValue);
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/**
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* Eventually sets the field of the given object managed by this
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* updater to the given updated value.
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*
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* @param obj An object whose field to set
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* @param newValue the new value
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* @since 1.6
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*/
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public abstract void lazySet(T obj, long newValue);
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/**
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* Gets the current value held in the field of the given object managed
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* by this updater.
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*
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* @param obj An object whose field to get
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* @return the current value
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*/
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public abstract long get(T obj);
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/**
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* Atomically sets the field of the given object managed by this updater
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* to the given value and returns the old value.
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*
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* @param obj An object whose field to get and set
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* @param newValue the new value
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* @return the previous value
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*/
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public long getAndSet(T obj, long newValue) {
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for (;;) {
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long current = get(obj);
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if (compareAndSet(obj, current, newValue))
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return current;
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}
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}
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/**
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* Atomically increments by one the current value of the field of the
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* given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @return the previous value
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*/
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public long getAndIncrement(T obj) {
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for (;;) {
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long current = get(obj);
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long next = current + 1;
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if (compareAndSet(obj, current, next))
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return current;
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}
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}
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/**
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* Atomically decrements by one the current value of the field of the
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* given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @return the previous value
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*/
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public long getAndDecrement(T obj) {
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for (;;) {
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long current = get(obj);
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long next = current - 1;
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if (compareAndSet(obj, current, next))
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return current;
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}
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}
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/**
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* Atomically adds the given value to the current value of the field of
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* the given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @param delta the value to add
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* @return the previous value
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*/
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public long getAndAdd(T obj, long delta) {
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for (;;) {
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long current = get(obj);
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long next = current + delta;
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if (compareAndSet(obj, current, next))
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return current;
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}
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}
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/**
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* Atomically increments by one the current value of the field of the
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* given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @return the updated value
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*/
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public long incrementAndGet(T obj) {
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for (;;) {
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long current = get(obj);
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long next = current + 1;
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if (compareAndSet(obj, current, next))
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return next;
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}
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}
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/**
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* Atomically decrements by one the current value of the field of the
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* given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @return the updated value
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*/
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public long decrementAndGet(T obj) {
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for (;;) {
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long current = get(obj);
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long next = current - 1;
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if (compareAndSet(obj, current, next))
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return next;
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}
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}
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/**
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* Atomically adds the given value to the current value of the field of
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* the given object managed by this updater.
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*
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* @param obj An object whose field to get and set
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* @param delta the value to add
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* @return the updated value
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*/
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public long addAndGet(T obj, long delta) {
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for (;;) {
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long current = get(obj);
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long next = current + delta;
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if (compareAndSet(obj, current, next))
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return next;
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}
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}
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private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
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private static final Unsafe unsafe = Unsafe.getUnsafe();
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private final long offset;
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private final Class<T> tclass;
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private final Class cclass;
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CASUpdater(Class<T> tclass, String fieldName) {
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Field field = null;
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Class caller = null;
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int modifiers = 0;
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try {
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field = tclass.getDeclaredField(fieldName);
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caller = sun.reflect.Reflection.getCallerClass(3);
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modifiers = field.getModifiers();
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sun.reflect.misc.ReflectUtil.ensureMemberAccess(
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caller, tclass, null, modifiers);
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sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
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} catch(Exception ex) {
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throw new RuntimeException(ex);
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}
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254 |
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|
255 |
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Class fieldt = field.getType();
|
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if (fieldt != long.class)
|
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throw new IllegalArgumentException("Must be long type");
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|
259 |
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if (!Modifier.isVolatile(modifiers))
|
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throw new IllegalArgumentException("Must be volatile type");
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|
262 |
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this.cclass = (Modifier.isProtected(modifiers) &&
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263 |
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caller != tclass) ? caller : null;
|
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this.tclass = tclass;
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offset = unsafe.objectFieldOffset(field);
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}
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|
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private void fullCheck(T obj) {
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269 |
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if (!tclass.isInstance(obj))
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throw new ClassCastException();
|
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if (cclass != null)
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ensureProtectedAccess(obj);
|
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}
|
274 |
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|
275 |
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public boolean compareAndSet(T obj, long expect, long update) {
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
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return unsafe.compareAndSwapLong(obj, offset, expect, update);
|
278 |
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}
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279 |
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|
280 |
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public boolean weakCompareAndSet(T obj, long expect, long update) {
|
281 |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
282 |
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return unsafe.compareAndSwapLong(obj, offset, expect, update);
|
283 |
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}
|
284 |
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|
285 |
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public void set(T obj, long newValue) {
|
286 |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
287 |
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unsafe.putLongVolatile(obj, offset, newValue);
|
288 |
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}
|
289 |
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|
290 |
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public void lazySet(T obj, long newValue) {
|
291 |
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
292 |
|
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unsafe.putOrderedLong(obj, offset, newValue);
|
293 |
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}
|
294 |
|
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|
295 |
|
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public long get(T obj) {
|
296 |
|
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if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
297 |
|
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return unsafe.getLongVolatile(obj, offset);
|
298 |
|
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}
|
299 |
|
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|
300 |
|
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private void ensureProtectedAccess(T obj) {
|
301 |
|
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if (cclass.isInstance(obj)) {
|
302 |
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return;
|
303 |
|
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}
|
304 |
|
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throw new RuntimeException (
|
305 |
|
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new IllegalAccessException("Class " +
|
306 |
|
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cclass.getName() +
|
307 |
|
|
" can not access a protected member of class " +
|
308 |
|
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tclass.getName() +
|
309 |
|
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" using an instance of " +
|
310 |
|
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obj.getClass().getName()
|
311 |
|
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)
|
312 |
|
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);
|
313 |
|
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}
|
314 |
|
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}
|
315 |
|
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|
316 |
|
|
|
317 |
|
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private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
|
318 |
|
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private static final Unsafe unsafe = Unsafe.getUnsafe();
|
319 |
|
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private final long offset;
|
320 |
|
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private final Class<T> tclass;
|
321 |
|
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private final Class cclass;
|
322 |
|
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|
323 |
|
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LockedUpdater(Class<T> tclass, String fieldName) {
|
324 |
|
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Field field = null;
|
325 |
|
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Class caller = null;
|
326 |
|
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int modifiers = 0;
|
327 |
|
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try {
|
328 |
|
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field = tclass.getDeclaredField(fieldName);
|
329 |
|
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caller = sun.reflect.Reflection.getCallerClass(3);
|
330 |
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modifiers = field.getModifiers();
|
331 |
|
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sun.reflect.misc.ReflectUtil.ensureMemberAccess(
|
332 |
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caller, tclass, null, modifiers);
|
333 |
|
|
sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);
|
334 |
|
|
} catch(Exception ex) {
|
335 |
|
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throw new RuntimeException(ex);
|
336 |
|
|
}
|
337 |
|
|
|
338 |
|
|
Class fieldt = field.getType();
|
339 |
|
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if (fieldt != long.class)
|
340 |
|
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throw new IllegalArgumentException("Must be long type");
|
341 |
|
|
|
342 |
|
|
if (!Modifier.isVolatile(modifiers))
|
343 |
|
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throw new IllegalArgumentException("Must be volatile type");
|
344 |
|
|
|
345 |
|
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this.cclass = (Modifier.isProtected(modifiers) &&
|
346 |
|
|
caller != tclass) ? caller : null;
|
347 |
|
|
this.tclass = tclass;
|
348 |
|
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offset = unsafe.objectFieldOffset(field);
|
349 |
|
|
}
|
350 |
|
|
|
351 |
|
|
private void fullCheck(T obj) {
|
352 |
|
|
if (!tclass.isInstance(obj))
|
353 |
|
|
throw new ClassCastException();
|
354 |
|
|
if (cclass != null)
|
355 |
|
|
ensureProtectedAccess(obj);
|
356 |
|
|
}
|
357 |
|
|
|
358 |
|
|
public boolean compareAndSet(T obj, long expect, long update) {
|
359 |
|
|
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
360 |
|
|
synchronized(this) {
|
361 |
|
|
long v = unsafe.getLong(obj, offset);
|
362 |
|
|
if (v != expect)
|
363 |
|
|
return false;
|
364 |
|
|
unsafe.putLong(obj, offset, update);
|
365 |
|
|
return true;
|
366 |
|
|
}
|
367 |
|
|
}
|
368 |
|
|
|
369 |
|
|
public boolean weakCompareAndSet(T obj, long expect, long update) {
|
370 |
|
|
return compareAndSet(obj, expect, update);
|
371 |
|
|
}
|
372 |
|
|
|
373 |
|
|
public void set(T obj, long newValue) {
|
374 |
|
|
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
375 |
|
|
synchronized(this) {
|
376 |
|
|
unsafe.putLong(obj, offset, newValue);
|
377 |
|
|
}
|
378 |
|
|
}
|
379 |
|
|
|
380 |
|
|
public void lazySet(T obj, long newValue) {
|
381 |
|
|
set(obj, newValue);
|
382 |
|
|
}
|
383 |
|
|
|
384 |
|
|
public long get(T obj) {
|
385 |
|
|
if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
|
386 |
|
|
synchronized(this) {
|
387 |
|
|
return unsafe.getLong(obj, offset);
|
388 |
|
|
}
|
389 |
|
|
}
|
390 |
|
|
|
391 |
|
|
private void ensureProtectedAccess(T obj) {
|
392 |
|
|
if (cclass.isInstance(obj)) {
|
393 |
|
|
return;
|
394 |
|
|
}
|
395 |
|
|
throw new RuntimeException (
|
396 |
|
|
new IllegalAccessException("Class " +
|
397 |
|
|
cclass.getName() +
|
398 |
|
|
" can not access a protected member of class " +
|
399 |
|
|
tclass.getName() +
|
400 |
|
|
" using an instance of " +
|
401 |
|
|
obj.getClass().getName()
|
402 |
|
|
)
|
403 |
|
|
);
|
404 |
|
|
}
|
405 |
|
|
}
|
406 |
|
|
}
|