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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;

/**

 * A <tt>long</tt> value that may be updated atomically.  See the

 * {@link java.util.concurrent.atomic} package specification for

 * description of the properties of atomic variables. An

 * <tt>AtomicLong</tt> is used in applications such as atomically

 * incremented sequence numbers, and cannot be used as a replacement

 * for a {@link java.lang.Long}. However, this class does extend

 * <tt>Number</tt> to allow uniform access by tools and utilities that

 * deal with numerically-based classes.

 *

 * @since 1.5

 * @author Doug Lea

 */

public class AtomicLong extends Number implements java.io.Serializable {

    private static final long serialVersionUID = 1927816293512124184L;

    // setup to use Unsafe.compareAndSwapLong for updates

    private static final Unsafe unsafe = Unsafe.getUnsafe();

    private static final long valueOffset;

    /**

     * Records whether the underlying JVM supports lockless

     * CompareAndSet for longs. While the unsafe.CompareAndSetLong

     * method works in either case, some constructions should be

     * handled at Java level to avoid locking user-visible locks.

     */

    static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();

    /**

     * Returns whether underlying JVM supports lockless CompareAndSet

     * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.

     */

    private static native boolean VMSupportsCS8();

    static {

      try {

        valueOffset = unsafe.objectFieldOffset

            (AtomicLong.class.getDeclaredField("value"));

      } catch (Exception ex) { throw new Error(ex); }

    }

    private volatile long value;

    /**

     * Creates a new AtomicLong with the given initial value.

     *

     * @param initialValue the initial value

     */

    public AtomicLong(long initialValue) {

        value = initialValue;

    }

    /**

     * Creates a new AtomicLong with initial value <tt>0</tt>.

     */

    public AtomicLong() {

    }

    /**

     * Gets the current value.

     *

     * @return the current value

     */

    public final long get() {

        return value;

    }

    /**

     * Sets to the given value.

     *

     * @param newValue the new value

     */

    public final void set(long newValue) {

        value = newValue;

    }

    /**

     * Eventually sets to the given value.

     *

     * @param newValue the new value

     * @since 1.6

     */

    public final void lazySet(long newValue) {

        unsafe.putOrderedLong(this, valueOffset, newValue);

    }

    /**

     * Atomically sets to the given value and returns the old value.

     *

     * @param newValue the new value

     * @return the previous value

     */

    public final long getAndSet(long newValue) {

        while (true) {

            long current = get();

            if (compareAndSet(current, newValue))

                return current;

        }

    }

    /**

     * 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(long expect, long update) {

        return unsafe.compareAndSwapLong(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(long expect, long update) {

        return unsafe.compareAndSwapLong(this, valueOffset, expect, update);

    }

    /**

     * Atomically increments by one the current value.

     *

     * @return the previous value

     */

    public final long getAndIncrement() {

        while (true) {

            long current = get();

            long next = current + 1;

            if (compareAndSet(current, next))

                return current;

        }

    }

    /**

     * Atomically decrements by one the current value.

     *

     * @return the previous value

     */

    public final long getAndDecrement() {

        while (true) {

            long current = get();

            long next = current - 1;

            if (compareAndSet(current, next))

                return current;

        }

    }

    /**

     * Atomically adds the given value to the current value.

     *

     * @param delta the value to add

     * @return the previous value

     */

    public final long getAndAdd(long delta) {

        while (true) {

            long current = get();

            long next = current + delta;

            if (compareAndSet(current, next))

                return current;

        }

    }

    /**

     * Atomically increments by one the current value.

     *

     * @return the updated value

     */

    public final long incrementAndGet() {

        for (;;) {

            long current = get();

            long next = current + 1;

            if (compareAndSet(current, next))

                return next;

        }

    }

    /**

     * Atomically decrements by one the current value.

     *

     * @return the updated value

     */

    public final long decrementAndGet() {

        for (;;) {

            long current = get();

            long next = current - 1;

            if (compareAndSet(current, next))

                return next;

        }

    }

    /**

     * Atomically adds the given value to the current value.

     *

     * @param delta the value to add

     * @return the updated value

     */

    public final long addAndGet(long delta) {

        for (;;) {

            long current = get();

            long next = current + delta;

            if (compareAndSet(current, next))

                return next;

        }

    }

    /**

     * Returns the String representation of the current value.

     * @return the String representation of the current value.

     */

    public String toString() {

        return Long.toString(get());

    }

    public int intValue() {

        return (int)get();

    }

    public long longValue() {

        return (long)get();

    }

    public float floatValue() {

        return (float)get();

    }

    public double doubleValue() {

        return (double)get();

    }

}