Java tutorial
/* * 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 java.lang.invoke.VarHandle; import java.util.function.IntBinaryOperator; import java.util.function.IntUnaryOperator; /** * 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 jdk.internal.misc.Unsafe U = jdk.internal.misc.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. * * @param initialValue the initial value */ public AtomicInteger(int initialValue) { value = initialValue; } /** * Creates a new AtomicInteger with initial value {@code 0}. */ public AtomicInteger() { } /** * 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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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 {@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. * @return the String representation of the current value */ public String toString() { return Integer.toString(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 {@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 {@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 {@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-{@code volatile}. * * @return the value * @since 9 */ public final int getPlain() { return U.getInt(this, VALUE); } /** * 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 {@link VarHandle#getOpaque}. * * @return the value * @since 9 */ public final int getOpaque() { return U.getIntOpaque(this, VALUE); } /** * 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 {@link VarHandle#getAcquire}. * * @return the value * @since 9 */ public final int getAcquire() { return U.getIntAcquire(this, VALUE); } /** * 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 {@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 {@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 {@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 {@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 {@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 {@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); } }