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/* |
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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/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent.atomic; |
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|
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import sun.misc.Unsafe; |
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|
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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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|
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private static final Unsafe unsafe = Unsafe.getUnsafe(); |
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private static final long valueOffset; |
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|
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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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|
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private volatile V value; |
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|
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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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/** |
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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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/** |
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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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/** |
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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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/** |
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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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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} 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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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} the expected value. |
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* |
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* <p><a href="package-summary.html#weakCompareAndSet">May fail |
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* spuriously and does not provide ordering guarantees</a>, so is |
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* only rarely an appropriate alternative to {@code compareAndSet}. |
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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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/** |
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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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/** |
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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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} |
