| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent.atomic; |
| import sun.misc.Unsafe; |
| |
| /** |
| * An object reference that may be updated atomically. See the {@link |
| * java.util.concurrent.atomic} package specification for description |
| * of the properties of atomic variables. |
| * @since 1.5 |
| * @author Doug Lea |
| * @param <V> The type of object referred to by this reference |
| */ |
| public class AtomicReference<V> implements java.io.Serializable { |
| private static final long serialVersionUID = -1848883965231344442L; |
| |
| private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| private static final long valueOffset; |
| |
| static { |
| try { |
| valueOffset = unsafe.objectFieldOffset |
| (AtomicReference.class.getDeclaredField("value")); |
| } catch (Exception ex) { throw new Error(ex); } |
| } |
| |
| private volatile V value; |
| |
| /** |
| * Creates a new AtomicReference with the given initial value. |
| * |
| * @param initialValue the initial value |
| */ |
| public AtomicReference(V initialValue) { |
| value = initialValue; |
| } |
| |
| /** |
| * Creates a new AtomicReference with null initial value. |
| */ |
| public AtomicReference() { |
| } |
| |
| /** |
| * Gets the current value. |
| * |
| * @return the current value |
| */ |
| public final V get() { |
| return value; |
| } |
| |
| /** |
| * Sets to the given value. |
| * |
| * @param newValue the new value |
| */ |
| public final void set(V newValue) { |
| value = newValue; |
| } |
| |
| /** |
| * Eventually sets to the given value. |
| * |
| * @param newValue the new value |
| * @since 1.6 |
| */ |
| public final void lazySet(V newValue) { |
| unsafe.putOrderedObject(this, valueOffset, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to the given updated value |
| * if the current value {@code ==} the expected value. |
| * @param expect the expected value |
| * @param update the new value |
| * @return true if successful. False return indicates that |
| * the actual value was not equal to the expected value. |
| */ |
| public final boolean compareAndSet(V expect, V update) { |
| return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
| } |
| |
| /** |
| * Atomically sets the value to the given updated value |
| * if the current value {@code ==} the expected value. |
| * |
| * <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
| * and does not provide ordering guarantees, so is only rarely an |
| * appropriate alternative to {@code compareAndSet}. |
| * |
| * @param expect the expected value |
| * @param update the new value |
| * @return true if successful. |
| */ |
| public final boolean weakCompareAndSet(V expect, V update) { |
| return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
| } |
| |
| /** |
| * Atomically sets to the given value and returns the old value. |
| * |
| * @param newValue the new value |
| * @return the previous value |
| */ |
| public final V getAndSet(V newValue) { |
| while (true) { |
| V x = get(); |
| if (compareAndSet(x, newValue)) |
| return x; |
| } |
| } |
| |
| /** |
| * Returns the String representation of the current value. |
| * @return the String representation of the current value. |
| */ |
| public String toString() { |
| return String.valueOf(get()); |
| } |
| |
| } |