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diff --git a/external/jsr166/java/util/concurrent/atomic/AtomicReference.java b/external/jsr166/java/util/concurrent/atomic/AtomicReference.java
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+/*
+ * 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/licenses/publicdomain
+ */
+
+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 <tt>==</tt> 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 <tt>==</tt> the expected value.
+     * May fail spuriously and does not provide ordering guarantees,
+     * so is only rarely an appropriate alternative to <tt>compareAndSet</tt>.
+     *
+     * @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());
+    }
+
+}