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JDK1.8
public class AtomicBoolean implements java.io.Serializable {private static final long serialVersionUID = 4654671469794556979L;// setup to use Unsafe.compareAndSwapInt for updates// 使用Unsafe.compareAndSwapInt进行更新private static final Unsafe unsafe = Unsafe.getUnsafe();// valueOffset是对象在内存中的偏移量private static final long valueOffset;//初始阶段，通过unsafe来获取AtomicBoolean类的value字段在内存中的偏移量valueOffsetstatic {try {valueOffset = unsafe.objectFieldOffset(AtomicBoolean.class.getDeclaredField("value"));} catch (Exception ex) { throw new Error(ex); }}//value被volatile修饰，保证其内存可见性，后面也会以value来判断AtomicBoolean值private volatile int value;/*** Creates a new {@code AtomicBoolean} with the given initial value.** @param initialValue the initial value*///构造方法：支持设置初始值，并且以int来存储 true -> 1 false -> 0public AtomicBoolean(boolean initialValue) {value = initialValue ? 1 : 0;}/*** Creates a new {@code AtomicBoolean} with initial value {@code false}.*///构造方法：没有赋值，没赋值的话，int默认为0， 0 -> falsepublic AtomicBoolean() {}/*** Returns the current value.** @return the current value*///获取当前value值 final修饰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 {@code true} if successful. False return indicates that* the actual value was not equal to the expected value.*///如果当前值 == 期望值expect，便会原子地更新成update值，返回true//如果当前值 != 期望值expect，更新失败，返回falsepublic 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><a href="package-summary.html#weakCompareAndSet">May fail* spuriously and does not provide ordering guarantees</a>, so is* only rarely an appropriate alternative to {@code compareAndSet}.** @param expect the expected value* @param update the new value* @return {@code true} if successful*///是的，这里和compareAndSet是一模一样的实现//有兴趣的可以百度下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*///不带任何条件地进行赋值，虽然value被volatile修饰，但是set这里修改不是原子方法public final void set(boolean newValue) {value = newValue ? 1 : 0;}/*** Eventually sets to the given value.** @param newValue the new value* @since 1.6*///注释的含义是：最终设置成功//和set方法对比来看，lazySet底层调用的是unsafe.putOrderedInt//从hotspot源码看putOrderedXXX源码分析底层操作//可以参考这个同学的分析，https://www.jianshu.com/p/4ed887664b13public 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*///原子地更新value值为newValue，并返回更新之前的值//先获取更新前的值，然后while一直尝试更新直到成功为止public final boolean getAndSet(boolean newValue) {boolean prev;do {prev = get();} while (!compareAndSet(prev, newValue));return prev;}/*** Returns the String representation of the current value.* @return the String representation of the current value*/public String toString() {return Boolean.toString(get());}}
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