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[/] [openrisc/] [trunk/] [gnu-dev/] [or1k-gcc/] [libjava/] [classpath/] [external/] [jsr166/] [java/] [util/] [concurrent/] [atomic/] [AtomicReference.java] - Blame information for rev 768

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Line No. Rev Author Line
1 768 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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/**
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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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