/*

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  */

 /*

  * This file is available under and governed by the GNU General Public

  * License version 2 only, as published by the Free Software Foundation.

  * However, the following notice accompanied the original version of this

  * file:

  *

  * 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;

 /**

  * A {@code long} value that may be updated atomically.  See the

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

  * description of the properties of atomic variables. An

  * {@code AtomicLong} 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

  * {@code Number} 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

      * compareAndSwap for longs. While the Unsafe.compareAndSwapLong

      * 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 {@code 0}.

      */

     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 {@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(long expect, long update) {

         return unsafe.compareAndSwapLong(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(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 get();

     }

     public float floatValue() {

         return (float)get();

     }

     public double doubleValue() {

         return (double)get();

     }

 }