AtomicReference

AtomicReference是作用是对”对象”进行原子操作。

源码

public class AtomicReference<V> implements Serializable {private static final long serialVersionUID = -1848883965231344442L;private static final Unsafe unsafe = Unsafe.getUnsafe();//通过 unsafe 实现原子操作private static final long valueOffset;private volatile V value;//通过 volatile 实现原子操作public AtomicReference(V var1) {this.value = var1;}public AtomicReference() {}//通过 volatile 实现原子操作public final V get() {return this.value;}//不是原子操作-慎用public final void set(V var1) {this.value = var1;}//通过 unsafe 实现原子操作public final void lazySet(V var1) {unsafe.putOrderedObject(this, valueOffset, var1);}//通过 unsafe 实现原子操作/*** var1当前值：拿当前值value和var1值去比较，如果相等返回true并更新值为var2期望值* var2期望值：如果返回true则更新为期望值，如果返回false则不更新值*/public final boolean compareAndSet(V var1, V var2) {return unsafe.compareAndSwapObject(this, valueOffset, var1, var2);}//通过 unsafe 实现原子操作public final boolean weakCompareAndSet(V var1, V var2) {return unsafe.compareAndSwapObject(this, valueOffset, var1, var2);}//通过 unsafe 实现原子操作public final V getAndSet(V var1) {return unsafe.getAndSetObject(this, valueOffset, var1);}//.....省略.....
}

使用

实体类

class People {private String name;private int age;public People(String name, int age) {this.name = name;this.age = age;}public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "People{" +"name='" + name + '\'' +", age=" + age +'}';}
}

    private static People p1 = new People("Tom", 12);private static People p2 = new People("Jack", 13);private static AtomicReference<People> ar = new AtomicReference(p1);public static void main(String[] args) throws InterruptedException {People people = ar.get();System.out.println(people == p1);//trueSystem.out.println(ar.compareAndSet(null, p2));//falseSystem.out.println(ar.get());//People{name='Tom', age=12}System.out.println(ar.compareAndSet(p1, p2));//trueSystem.out.println(ar.get());//People{name='Jack', age=13}}

AtomicReference和AtomicInteger一样，有ABA问题，用AtomicStampedReference解决

public class Test {private static People p1 = new People("Tom", 12);private static People p2 = new People("Jack", 13);private static AtomicReference<People> at = new AtomicReference(p1);private static AtomicStampedReference<People> asr = new AtomicStampedReference(p1, 0);public static void main(String[] args) throws InterruptedException {Thread t1 = new Thread(() -> {try {TimeUnit.SECONDS.sleep(1);at.compareAndSet(p1, p2);at.compareAndSet(p2, p1);} catch (InterruptedException e) {e.printStackTrace();}});t1.start();Thread t2 = new Thread(() -> {try {TimeUnit.SECONDS.sleep(2);boolean b = at.compareAndSet(p1, p2);System.out.println("AtomicReference " + b);//AtomicReference true} catch (InterruptedException e) {e.printStackTrace();}});t2.start();Thread t3 = new Thread(() -> {try {TimeUnit.SECONDS.sleep(1);asr.compareAndSet(p1, p2, asr.getStamp(), asr.getStamp() + 1);asr.compareAndSet(p2, p1, asr.getStamp(), asr.getStamp() + 1);} catch (InterruptedException e) {e.printStackTrace();}});t3.start();Thread t4 = new Thread(() -> {try {int stamp = asr.getStamp();TimeUnit.SECONDS.sleep(2);boolean b = asr.compareAndSet(p1, p2, stamp, stamp + 1);System.out.println("AtomicStampedReference " + b);//AtomicStampedReference false} catch (InterruptedException e) {e.printStackTrace();}});t4.start();}}

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AtomicReference

源码

使用

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