Java 源码 - java.util.concurrent.atomic.AtomicReference

概述

AtomicReference 是一个 Java concurrent 包提供的一个原子类，通过这个类可以进行一些原子操作。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 AtomicReference<V> implements java.io.Serializable

成员属性

    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final long valueOffset;
    private volatile V value;

静态代码块

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

构造方法

    public AtomicReference(V initialValue) {
        value = initialValue;
    }

    public AtomicReference() {
    }

第一个方法在初始的时候就传入初始值， 而第二的方法是一个空方法。

基本方法

    public final boolean compareAndSet(V expect, V update) {
        return unsafe.compareAndSwapObject(this, valueOffset, expect, update);
    }

    public final V getAndSet(V newValue) {
        return (V)unsafe.getAndSetObject(this, valueOffset, newValue);
    }

    public final V getAndUpdate(UnaryOperator<V> updateFunction) {
        V prev, next;
        do {
            prev = get();
            next = updateFunction.apply(prev);
        } while (!compareAndSet(prev, next));
        return prev;
    }

    public final V updateAndGet(UnaryOperator<V> updateFunction) {
        V prev, next;
        do {
            prev = get();
            next = updateFunction.apply(prev);
        } while (!compareAndSet(prev, next));
        return next;
    }

    public final V getAndAccumulate(V x,
                                    BinaryOperator<V> accumulatorFunction) {
        V prev, next;
        do {
            prev = get();
            next = accumulatorFunction.apply(prev, x);
        } while (!compareAndSet(prev, next));
        return prev;
    }

    public final V accumulateAndGet(V x,
                                    BinaryOperator<V> accumulatorFunction) {
        V prev, next;
        do {
            prev = get();
            next = accumulatorFunction.apply(prev, x);
        } while (!compareAndSet(prev, next));
        return next;
    }