/*
* 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
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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/licenses/publicdomain
*/
package java.util.concurrent.atomic;
import sun.misc.Unsafe;
/**
* A {@code boolean} 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 AtomicBoolean} is used in applications such as atomically
* updated flags, and cannot be used as a replacement for a
* {@link java.lang.Boolean}.
*
* @since 1.5
* @author Doug Lea
*/
public class AtomicBoolean implements java.io.Serializable {
private static final long serialVersionUID = 4654671469794556979L;
// setup to use Unsafe.compareAndSwapInt for updates
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final long valueOffset;
static {
try {
valueOffset = unsafe.objectFieldOffset
(AtomicBoolean.class.getDeclaredField("value"));
} catch (Exception ex) { throw new Error(ex); }
}
private volatile int value;
/**
* Creates a new {@code AtomicBoolean} with the given initial value.
*
* @param initialValue the initial value
*/
public AtomicBoolean(boolean initialValue) {
value = initialValue ? 1 : 0;
}
/**
* Creates a new {@code AtomicBoolean} with initial value {@code false}.
*/
public AtomicBoolean() {
}
/**
* Returns the current value.
*
* @return the current value
*/
public final boolean get() {
return value != 0;
}
/**
* 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(boolean expect, boolean update) {
int e = expect ? 1 : 0;
int u = update ? 1 : 0;
return unsafe.compareAndSwapInt(this, valueOffset, e, u);
}
/**
* 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 boolean weakCompareAndSet(boolean expect, boolean update) {
int e = expect ? 1 : 0;
int u = update ? 1 : 0;
return unsafe.compareAndSwapInt(this, valueOffset, e, u);
}
/**
* Unconditionally sets to the given value.
*
* @param newValue the new value
*/
public final void set(boolean newValue) {
value = newValue ? 1 : 0;
}
/**
* Eventually sets to the given value.
*
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(boolean newValue) {
int v = newValue ? 1 : 0;
unsafe.putOrderedInt(this, valueOffset, v);
}
/**
* Atomically sets to the given value and returns the previous value.
*
* @param newValue the new value
* @return the previous value
*/
public final boolean getAndSet(boolean newValue) {
for (;;) {
boolean current = get();
if (compareAndSet(current, newValue))
return current;
}
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value.
*/
public String toString() {
return Boolean.toString(get());
}
}