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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 <tt>int</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>AtomicInteger</tt> is used in applications such as atomically

 * incremented counters, and cannot be used as a replacement for an

 * {@link java.lang.Integer}. 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 AtomicInteger extends Number implements java.io.Serializable {

    private static final long serialVersionUID = 6214790243416807050L;

    // setup to use Unsafe.compareAndSwapInt for updates

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

    private static final long valueOffset;

    static {

      try {

        valueOffset = unsafe.objectFieldOffset

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

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

    }

    private volatile int value;

    /**

     * Creates a new AtomicInteger with the given initial value.

     *

     * @param initialValue the initial value

     */

    public AtomicInteger(int initialValue) {

        value = initialValue;

    }

    /**

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

     */

    public AtomicInteger() {

    }

    /**

     * Gets the current value.

     *

     * @return the current value

     */

    public final int get() {

        return value;

    }

    /**

     * Sets to the given value.

     *

     * @param newValue the new value

     */

    public final void set(int newValue) {

        value = newValue;

    }

    /**

     * Eventually sets to the given value.

     *

     * @param newValue the new value

     * @since 1.6

     */

    public final void lazySet(int newValue) {

        unsafe.putOrderedInt(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 int getAndSet(int newValue) {

        for (;;) {

            int 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(int expect, int update) {

        return unsafe.compareAndSwapInt(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(int expect, int update) {

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

    }

    /**

     * Atomically increments by one the current value.

     *

     * @return the previous value

     */

    public final int getAndIncrement() {

        for (;;) {

            int current = get();

            int next = current + 1;

            if (compareAndSet(current, next))

                return current;

        }

    }

    /**

     * Atomically decrements by one the current value.

     *

     * @return the previous value

     */

    public final int getAndDecrement() {

        for (;;) {

            int current = get();

            int 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 int getAndAdd(int delta) {

        for (;;) {

            int current = get();

            int next = current + delta;

            if (compareAndSet(current, next))

                return current;

        }

    }

    /**

     * Atomically increments by one the current value.

     *

     * @return the updated value

     */

    public final int incrementAndGet() {

        for (;;) {

            int current = get();

            int next = current + 1;

            if (compareAndSet(current, next))

                return next;

        }

    }

    /**

     * Atomically decrements by one the current value.

     *

     * @return the updated value

     */

    public final int decrementAndGet() {

        for (;;) {

            int current = get();

            int 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 int addAndGet(int delta) {

        for (;;) {

            int current = get();

            int 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 Integer.toString(get());

    }

    public int intValue() {

        return get();

    }

    public long longValue() {

        return (long)get();

    }

    public float floatValue() {

        return (float)get();

    }

    public double doubleValue() {

        return (double)get();

    }

}