libcore/concurrent/src/main/java/java/util/concurrent/atomic/AtomicInteger.java

/*
 * 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
    // BEGIN android-changed
    private static final Unsafe unsafe = UnsafeAccess.THE_ONE;
    // END android-changed
    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;

    /**
     * Create a new AtomicInteger with the given initial value.
     *
     * @param initialValue the initial value
     */
    public AtomicInteger(int initialValue) {
        value = initialValue;
    }

    /**
     * Create a new AtomicInteger with initial value <tt>0</tt>.
     */
    public AtomicInteger() {
    }

    /**
     * Get the current value.
     *
     * @return the current value
     */
    public final int get() {
        return value;
    }
  
    /**
     * Set to the given value.
     *
     * @param newValue the new value
     */
    public final void set(int newValue) {
        value = newValue;
    }

    /**
     * Set to the give value and return 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 set 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 set the value to the given updated value
     * if the current value <tt>==</tt> the expected value.
     * May fail spuriously.
     * @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 increment 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 decrement 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 add the given value to 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 increment 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 decrement 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 add the given value to 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();
    }

}