Java 源码 - java.util.concurrent.atomic.AtomicBoolean概述AtomicB

概述

AtomicBoolean 是一个 Java concurrent 包提供的一个原子类，通过这个类可以对 Boolean 进行一些原子操作。这个类的源码比较简单，主要是依赖于 sun.misc.Unsafe 提供的一些 native 方法保证操作的原子性。

继承关系

public class AtomicBoolean implements java.io.Serializable

成员属性

    // setup to use Unsafe.compareAndSwapInt for updates
    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;
    private volatile int value;

静态代码块

    static {
        try {
            valueOffset = unsafe.objectFieldOffset
                (AtomicBoolean.class.getDeclaredField("value"));
        } catch (Exception ex) { throw new Error(ex); }
    }

构造方法

    public AtomicBoolean(boolean initialValue) {
        value = initialValue ? 1 : 0;
    }

    public AtomicBoolean() { }

True: 1 False: 0

基本方法

    public final boolean get() {
        return value != 0;
    }

    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);
    }

    public final void set(boolean newValue) {
        value = newValue ? 1 : 0;
    }

    public final void lazySet(boolean newValue) {
        int v = newValue ? 1 : 0;
        unsafe.putOrderedInt(this, valueOffset, v);
    }

    public final boolean getAndSet(boolean newValue) {
        boolean prev;
        do {
            prev = get();
        } while (!compareAndSet(prev, newValue));
        return prev;
    }

    public String toString() {
        return Boolean.toString(get());
    }