mirror of git://gcc.gnu.org/git/gcc.git
125 lines
3.4 KiB
Java
125 lines
3.4 KiB
Java
/*
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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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/**
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* An object reference that may be updated atomically. See the {@link
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* java.util.concurrent.atomic} package specification for description
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* of the properties of atomic variables.
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* @since 1.5
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* @author Doug Lea
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* @param <V> The type of object referred to by this reference
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*/
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public class AtomicReference<V> implements java.io.Serializable {
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private static final long serialVersionUID = -1848883965231344442L;
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private static final Unsafe unsafe = Unsafe.getUnsafe();
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private static final long valueOffset;
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static {
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try {
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valueOffset = unsafe.objectFieldOffset
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(AtomicReference.class.getDeclaredField("value"));
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} catch (Exception ex) { throw new Error(ex); }
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}
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private volatile V value;
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/**
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* Creates a new AtomicReference with the given initial value.
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*
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* @param initialValue the initial value
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*/
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public AtomicReference(V initialValue) {
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value = initialValue;
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}
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/**
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* Creates a new AtomicReference with null initial value.
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*/
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public AtomicReference() {
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}
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/**
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* Gets the current value.
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*
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* @return the current value
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*/
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public final V get() {
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return value;
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}
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/**
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* Sets to the given value.
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*
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* @param newValue the new value
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*/
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public final void set(V newValue) {
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value = newValue;
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}
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/**
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* Eventually sets to the given value.
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*
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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 final void lazySet(V newValue) {
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unsafe.putOrderedObject(this, valueOffset, newValue);
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}
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/**
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* Atomically sets the value to the given updated value
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* if the current value <tt>==</tt> the expected value.
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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. False return indicates that
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* the actual value was not equal to the expected value.
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*/
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public final boolean compareAndSet(V expect, V update) {
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return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
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}
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/**
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* Atomically sets the value to the given updated value
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* if the current value <tt>==</tt> the expected value.
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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 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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*/
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public final boolean weakCompareAndSet(V expect, V update) {
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return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
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}
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/**
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* Atomically sets to the given value and returns the old value.
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*
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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 final V getAndSet(V newValue) {
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while (true) {
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V x = get();
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if (compareAndSet(x, newValue))
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return x;
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}
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}
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/**
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* Returns the String representation of the current value.
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* @return the String representation of the current value.
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*/
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public String toString() {
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return String.valueOf(get());
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}
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}
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