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/*
 * 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
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/*
 * 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 java.lang.invoke.VarHandle;
import java.util.function.IntBinaryOperator;
import java.util.function.IntUnaryOperator;
import jdk.internal.misc.Unsafe;


An int value that may be updated atomically. See the VarHandle specification for descriptions of the properties of atomic accesses. An AtomicInteger is used in applications such as atomically incremented counters, and cannot be used as a replacement for an Integer. However, this class does extend Number to allow uniform access by tools and utilities that deal with numerically-based classes. 
Author:Doug Lea
Since:1.5
/**
 * An {@code int} value that may be updated atomically.  See the
 * {@link VarHandle} specification for descriptions of the properties
 * of atomic accesses. An {@code AtomicInteger} 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 {@code Number} 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;

    /*
     * This class intended to be implemented using VarHandles, but there
     * are unresolved cyclic startup dependencies.
     */
    private static final Unsafe U = Unsafe.getUnsafe();
    private static final long VALUE
        = U.objectFieldOffset(AtomicInteger.class, "value");

    private volatile int value;

    
Creates a new AtomicInteger with the given initial value.

Params:
  • initialValue – the initial 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 0. 
/**
     * Creates a new AtomicInteger with initial value {@code 0}.
     */
    public AtomicInteger() {
    }

    
Returns the current value, with memory effects as specified by VarHandle.getVolatile. 
Returns:the current value
/**
     * Returns the current value,
     * with memory effects as specified by {@link VarHandle#getVolatile}.
     *
     * @return the current value
     */
    public final int get() {
        return value;
    }

    
Sets the value to newValue, with memory effects as specified by VarHandle.setVolatile. 
Params:
  • newValue – the new value
/**
     * Sets the value to {@code newValue},
     * with memory effects as specified by {@link VarHandle#setVolatile}.
     *
     * @param newValue the new value
     */
    public final void set(int newValue) {
        value = newValue;
    }

    
Sets the value to newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • newValue – the new value
Since:1.6
/**
     * Sets the value to {@code newValue},
     * with memory effects as specified by {@link VarHandle#setRelease}.
     *
     * @param newValue the new value
     * @since 1.6
     */
    public final void lazySet(int newValue) {
        U.putIntRelease(this, VALUE, newValue);
    }

    
Atomically sets the value to newValue and returns the old value, with memory effects as specified by VarHandle.getAndSet. 
Params:
  • newValue – the new value
Returns:the previous value
/**
     * Atomically sets the value to {@code newValue} and returns the old value,
     * with memory effects as specified by {@link VarHandle#getAndSet}.
     *
     * @param newValue the new value
     * @return the previous value
     */
    public final int getAndSet(int newValue) {
        return U.getAndSetInt(this, VALUE, newValue);
    }

    
Atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.compareAndSet. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful. False return indicates that the actual value was not equal to the expected value.
/**
     * Atomically sets the value to {@code newValue}
     * if the current value {@code == expectedValue},
     * with memory effects as specified by {@link VarHandle#compareAndSet}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful. False return indicates that
     * the actual value was not equal to the expected value.
     */
    public final boolean compareAndSet(int expectedValue, int newValue) {
        return U.compareAndSetInt(this, VALUE, expectedValue, newValue);
    }

    
Possibly atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
See Also:
Deprecated:This method has plain memory effects but the method name implies volatile memory effects (see methods such as compareAndExchange and compareAndSet). To avoid confusion over plain or volatile memory effects it is recommended that the method weakCompareAndSetPlain be used instead.
Returns:true if successful
/**
     * Possibly atomically sets the value to {@code newValue}
     * if the current value {@code == expectedValue},
     * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
     *
     * @deprecated This method has plain memory effects but the method
     * name implies volatile memory effects (see methods such as
     * {@link #compareAndExchange} and {@link #compareAndSet}).  To avoid
     * confusion over plain or volatile memory effects it is recommended that
     * the method {@link #weakCompareAndSetPlain} be used instead.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @see #weakCompareAndSetPlain
     */
    @Deprecated(since="9")
    public final boolean weakCompareAndSet(int expectedValue, int newValue) {
        return U.weakCompareAndSetIntPlain(this, VALUE, expectedValue, newValue);
    }

    
Possibly atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetPlain. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * Possibly atomically sets the value to {@code newValue}
     * if the current value {@code == expectedValue},
     * with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetPlain(int expectedValue, int newValue) {
        return U.weakCompareAndSetIntPlain(this, VALUE, expectedValue, newValue);
    }

    
Atomically increments the current value, with memory effects as specified by VarHandle.getAndAdd. 
Equivalent to getAndAdd(1). 
Returns:the previous value
/**
     * Atomically increments the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * <p>Equivalent to {@code getAndAdd(1)}.
     *
     * @return the previous value
     */
    public final int getAndIncrement() {
        return U.getAndAddInt(this, VALUE, 1);
    }

    
Atomically decrements the current value, with memory effects as specified by VarHandle.getAndAdd. 
Equivalent to getAndAdd(-1). 
Returns:the previous value
/**
     * Atomically decrements the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * <p>Equivalent to {@code getAndAdd(-1)}.
     *
     * @return the previous value
     */
    public final int getAndDecrement() {
        return U.getAndAddInt(this, VALUE, -1);
    }

    
Atomically adds the given value to the current value, with memory effects as specified by VarHandle.getAndAdd. 
Params:
  • delta – the value to add
Returns:the previous value
/**
     * Atomically adds the given value to the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * @param delta the value to add
     * @return the previous value
     */
    public final int getAndAdd(int delta) {
        return U.getAndAddInt(this, VALUE, delta);
    }

    
Atomically increments the current value, with memory effects as specified by VarHandle.getAndAdd. 
Equivalent to addAndGet(1). 
Returns:the updated value
/**
     * Atomically increments the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * <p>Equivalent to {@code addAndGet(1)}.
     *
     * @return the updated value
     */
    public final int incrementAndGet() {
        return U.getAndAddInt(this, VALUE, 1) + 1;
    }

    
Atomically decrements the current value, with memory effects as specified by VarHandle.getAndAdd. 
Equivalent to addAndGet(-1). 
Returns:the updated value
/**
     * Atomically decrements the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * <p>Equivalent to {@code addAndGet(-1)}.
     *
     * @return the updated value
     */
    public final int decrementAndGet() {
        return U.getAndAddInt(this, VALUE, -1) - 1;
    }

    
Atomically adds the given value to the current value, with memory effects as specified by VarHandle.getAndAdd. 
Params:
  • delta – the value to add
Returns:the updated value
/**
     * Atomically adds the given value to the current value,
     * with memory effects as specified by {@link VarHandle#getAndAdd}.
     *
     * @param delta the value to add
     * @return the updated value
     */
    public final int addAndGet(int delta) {
        return U.getAndAddInt(this, VALUE, delta) + delta;
    }

    
Atomically updates (with memory effects as specified by VarHandle.compareAndSet) the current value with the results of applying the given function, returning the previous value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. 
Params:
  • updateFunction – a side-effect-free function
Returns:the previous value
Since:1.8
/**
     * Atomically updates (with memory effects as specified by {@link
     * VarHandle#compareAndSet}) the current value with the results of
     * applying the given function, returning the previous value. The
     * function should be side-effect-free, since it may be re-applied
     * when attempted updates fail due to contention among threads.
     *
     * @param updateFunction a side-effect-free function
     * @return the previous value
     * @since 1.8
     */
    public final int getAndUpdate(IntUnaryOperator updateFunction) {
        int prev = get(), next = 0;
        for (boolean haveNext = false;;) {
            if (!haveNext)
                next = updateFunction.applyAsInt(prev);
            if (weakCompareAndSetVolatile(prev, next))
                return prev;
            haveNext = (prev == (prev = get()));
        }
    }

    
Atomically updates (with memory effects as specified by VarHandle.compareAndSet) the current value with the results of applying the given function, returning the updated value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. 
Params:
  • updateFunction – a side-effect-free function
Returns:the updated value
Since:1.8
/**
     * Atomically updates (with memory effects as specified by {@link
     * VarHandle#compareAndSet}) the current value with the results of
     * applying the given function, returning the updated value. The
     * function should be side-effect-free, since it may be re-applied
     * when attempted updates fail due to contention among threads.
     *
     * @param updateFunction a side-effect-free function
     * @return the updated value
     * @since 1.8
     */
    public final int updateAndGet(IntUnaryOperator updateFunction) {
        int prev = get(), next = 0;
        for (boolean haveNext = false;;) {
            if (!haveNext)
                next = updateFunction.applyAsInt(prev);
            if (weakCompareAndSetVolatile(prev, next))
                return next;
            haveNext = (prev == (prev = get()));
        }
    }

    
Atomically updates (with memory effects as specified by VarHandle.compareAndSet) the current value with the results of applying the given function to the current and given values, returning the previous value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value as its first argument, and the given update as the second argument. 
Params:
  • x – the update value
  • accumulatorFunction – a side-effect-free function of two arguments
Returns:the previous value
Since:1.8
/**
     * Atomically updates (with memory effects as specified by {@link
     * VarHandle#compareAndSet}) the current value with the results of
     * applying the given function to the current and given values,
     * returning the previous value. The function should be
     * side-effect-free, since it may be re-applied when attempted
     * updates fail due to contention among threads.  The function is
     * applied with the current value as its first argument, and the
     * given update as the second argument.
     *
     * @param x the update value
     * @param accumulatorFunction a side-effect-free function of two arguments
     * @return the previous value
     * @since 1.8
     */
    public final int getAndAccumulate(int x,
                                      IntBinaryOperator accumulatorFunction) {
        int prev = get(), next = 0;
        for (boolean haveNext = false;;) {
            if (!haveNext)
                next = accumulatorFunction.applyAsInt(prev, x);
            if (weakCompareAndSetVolatile(prev, next))
                return prev;
            haveNext = (prev == (prev = get()));
        }
    }

    
Atomically updates (with memory effects as specified by VarHandle.compareAndSet) the current value with the results of applying the given function to the current and given values, returning the updated value. The function should be side-effect-free, since it may be re-applied when attempted updates fail due to contention among threads. The function is applied with the current value as its first argument, and the given update as the second argument. 
Params:
  • x – the update value
  • accumulatorFunction – a side-effect-free function of two arguments
Returns:the updated value
Since:1.8
/**
     * Atomically updates (with memory effects as specified by {@link
     * VarHandle#compareAndSet}) the current value with the results of
     * applying the given function to the current and given values,
     * returning the updated value. The function should be
     * side-effect-free, since it may be re-applied when attempted
     * updates fail due to contention among threads.  The function is
     * applied with the current value as its first argument, and the
     * given update as the second argument.
     *
     * @param x the update value
     * @param accumulatorFunction a side-effect-free function of two arguments
     * @return the updated value
     * @since 1.8
     */
    public final int accumulateAndGet(int x,
                                      IntBinaryOperator accumulatorFunction) {
        int prev = get(), next = 0;
        for (boolean haveNext = false;;) {
            if (!haveNext)
                next = accumulatorFunction.applyAsInt(prev, x);
            if (weakCompareAndSetVolatile(prev, next))
                return next;
            haveNext = (prev == (prev = get()));
        }
    }

    
Returns the String representation of the current value.

Returns:the String representation of the current value
/**
     * Returns the String representation of the current value.
     * @return the String representation of the current value
     */
    public String toString() {
        return Integer.toString(get());
    }

    
Returns the current value of this AtomicInteger as an int, with memory effects as specified by VarHandle.getVolatile. Equivalent to get(). 
/**
     * Returns the current value of this {@code AtomicInteger} as an
     * {@code int},
     * with memory effects as specified by {@link VarHandle#getVolatile}.
     *
     * Equivalent to {@link #get()}.
     */
    public int intValue() {
        return get();
    }

    
Returns the current value of this AtomicInteger as a long after a widening primitive conversion, with memory effects as specified by VarHandle.getVolatile. 
@jls5.1.2 Widening Primitive Conversion
/**
     * Returns the current value of this {@code AtomicInteger} as a
     * {@code long} after a widening primitive conversion,
     * with memory effects as specified by {@link VarHandle#getVolatile}.
     * @jls 5.1.2 Widening Primitive Conversion
     */
    public long longValue() {
        return (long)get();
    }

    
Returns the current value of this AtomicInteger as a float after a widening primitive conversion, with memory effects as specified by VarHandle.getVolatile. 
@jls5.1.2 Widening Primitive Conversion
/**
     * Returns the current value of this {@code AtomicInteger} as a
     * {@code float} after a widening primitive conversion,
     * with memory effects as specified by {@link VarHandle#getVolatile}.
     * @jls 5.1.2 Widening Primitive Conversion
     */
    public float floatValue() {
        return (float)get();
    }

    
Returns the current value of this AtomicInteger as a double after a widening primitive conversion, with memory effects as specified by VarHandle.getVolatile. 
@jls5.1.2 Widening Primitive Conversion
/**
     * Returns the current value of this {@code AtomicInteger} as a
     * {@code double} after a widening primitive conversion,
     * with memory effects as specified by {@link VarHandle#getVolatile}.
     * @jls 5.1.2 Widening Primitive Conversion
     */
    public double doubleValue() {
        return (double)get();
    }

    // jdk9

    
Returns the current value, with memory semantics of reading as if the variable was declared non-volatile. 
Returns:the value
Since:9
/**
     * Returns the current value, with memory semantics of reading as
     * if the variable was declared non-{@code volatile}.
     *
     * @return the value
     * @since 9
     */
    public final int getPlain() {
        return U.getInt(this, VALUE);
    }

    
Sets the value to newValue, with memory semantics of setting as if the variable was declared non-volatile and non-final. 
Params:
  • newValue – the new value
Since:9
/**
     * Sets the value to {@code newValue}, with memory semantics
     * of setting as if the variable was declared non-{@code volatile}
     * and non-{@code final}.
     *
     * @param newValue the new value
     * @since 9
     */
    public final void setPlain(int newValue) {
        U.putInt(this, VALUE, newValue);
    }

    
Returns the current value, with memory effects as specified by VarHandle.getOpaque. 
Returns:the value
Since:9
/**
     * Returns the current value,
     * with memory effects as specified by {@link VarHandle#getOpaque}.
     *
     * @return the value
     * @since 9
     */
    public final int getOpaque() {
        return U.getIntOpaque(this, VALUE);
    }

    
Sets the value to newValue, with memory effects as specified by VarHandle.setOpaque. 
Params:
  • newValue – the new value
Since:9
/**
     * Sets the value to {@code newValue},
     * with memory effects as specified by {@link VarHandle#setOpaque}.
     *
     * @param newValue the new value
     * @since 9
     */
    public final void setOpaque(int newValue) {
        U.putIntOpaque(this, VALUE, newValue);
    }

    
Returns the current value, with memory effects as specified by VarHandle.getAcquire. 
Returns:the value
Since:9
/**
     * Returns the current value,
     * with memory effects as specified by {@link VarHandle#getAcquire}.
     *
     * @return the value
     * @since 9
     */
    public final int getAcquire() {
        return U.getIntAcquire(this, VALUE);
    }

    
Sets the value to newValue, with memory effects as specified by VarHandle.setRelease. 
Params:
  • newValue – the new value
Since:9
/**
     * Sets the value to {@code newValue},
     * with memory effects as specified by {@link VarHandle#setRelease}.
     *
     * @param newValue the new value
     * @since 9
     */
    public final void setRelease(int newValue) {
        U.putIntRelease(this, VALUE, newValue);
    }

    
Atomically sets the value to newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchange. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * Atomically sets the value to {@code newValue} if the current value,
     * referred to as the <em>witness value</em>, {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#compareAndExchange}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return the witness value, which will be the same as the
     * expected value if successful
     * @since 9
     */
    public final int compareAndExchange(int expectedValue, int newValue) {
        return U.compareAndExchangeInt(this, VALUE, expectedValue, newValue);
    }

    
Atomically sets the value to newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeAcquire. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * Atomically sets the value to {@code newValue} if the current value,
     * referred to as the <em>witness value</em>, {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#compareAndExchangeAcquire}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return the witness value, which will be the same as the
     * expected value if successful
     * @since 9
     */
    public final int compareAndExchangeAcquire(int expectedValue, int newValue) {
        return U.compareAndExchangeIntAcquire(this, VALUE, expectedValue, newValue);
    }

    
Atomically sets the value to newValue if the current value, referred to as the witness value, == expectedValue, with memory effects as specified by VarHandle.compareAndExchangeRelease. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:the witness value, which will be the same as the
expected value if successful
Since:9
/**
     * Atomically sets the value to {@code newValue} if the current value,
     * referred to as the <em>witness value</em>, {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#compareAndExchangeRelease}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return the witness value, which will be the same as the
     * expected value if successful
     * @since 9
     */
    public final int compareAndExchangeRelease(int expectedValue, int newValue) {
        return U.compareAndExchangeIntRelease(this, VALUE, expectedValue, newValue);
    }

    
Possibly atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSet. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * Possibly atomically sets the value to {@code newValue} if
     * the current value {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#weakCompareAndSet}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetVolatile(int expectedValue, int newValue) {
        return U.weakCompareAndSetInt(this, VALUE, expectedValue, newValue);
    }

    
Possibly atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetAcquire. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * Possibly atomically sets the value to {@code newValue} if
     * the current value {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#weakCompareAndSetAcquire}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetAcquire(int expectedValue, int newValue) {
        return U.weakCompareAndSetIntAcquire(this, VALUE, expectedValue, newValue);
    }

    
Possibly atomically sets the value to newValue if the current value == expectedValue, with memory effects as specified by VarHandle.weakCompareAndSetRelease. 
Params:
  • expectedValue – the expected value
  • newValue – the new value
Returns:true if successful
Since:9
/**
     * Possibly atomically sets the value to {@code newValue} if
     * the current value {@code == expectedValue},
     * with memory effects as specified by
     * {@link VarHandle#weakCompareAndSetRelease}.
     *
     * @param expectedValue the expected value
     * @param newValue the new value
     * @return {@code true} if successful
     * @since 9
     */
    public final boolean weakCompareAndSetRelease(int expectedValue, int newValue) {
        return U.weakCompareAndSetIntRelease(this, VALUE, expectedValue, newValue);
    }

}