java并发AtomicReference

java并发AtomicReference

AtomicReference的作用

已经介绍过AtomicInteger,AtomicIntegerArray，AtomicReference是针对对象的。

他通过CAS和volatile保证了对象操作的原子性和可见性，既然是引用，就会造成引用对象的变化。

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

如果value改变了对象的属性，initialValue的属性也会改变

CAS函数的实现

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

例子

package javalearn.javabase.thread.atomic;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.ToString;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.atomic.AtomicReference;
@Slf4j
public class AtomicReferanceTest {
    public static void main(String[] args) {
        Persion p1 = new Persion("jack", 1);
        Persion p2 = new Persion("linda", 2);
        Persion p3 = new Persion("tony", 3);
        log.info("persion 3 :{}",p3.toString());
        AtomicReference<Persion> atomicReference =new AtomicReference(p3);
        log.info("AtomicReference is :{}",atomicReference.toString());
        atomicReference.compareAndSet(p3,p1);
        log.info("AtomicReference is :{}",atomicReference.toString());
        log.info("persion 3 :{}",p3.toString());
        atomicReference.set(p2);
        log.info("AtomicReference is :{}",atomicReference.toString());
        log.info("persion 3 :{}",p3.toString());
        atomicReference.get().setId(33);
        log.info("AtomicReference is :{}",atomicReference.toString());
        log.info("AtomicReference is :{}",atomicReference.toString());
        log.info("persion 3 :{}",p3.toString());
        log.info("persion 2 :{}",p2.toString());
    }
    @AllArgsConstructor
    @Data
    @ToString
    static class Persion {
        private String name;
        private int id;
    }
}

结果

13:34:22.313 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - persion 3 :AtomicReferanceTest.Persion(name=tony, id=3)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - AtomicReference is :AtomicReferanceTest.Persion(name=tony, id=3)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - AtomicReference is :AtomicReferanceTest.Persion(name=jack, id=1)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - persion 3 :AtomicReferanceTest.Persion(name=tony, id=3)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - AtomicReference is :AtomicReferanceTest.Persion(name=linda, id=2)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - persion 3 :AtomicReferanceTest.Persion(name=tony, id=3)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - AtomicReference is :AtomicReferanceTest.Persion(name=linda, id=33)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - AtomicReference is :AtomicReferanceTest.Persion(name=linda, id=33)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - persion 3 :AtomicReferanceTest.Persion(name=tony, id=3)
13:34:22.321 [main] INFO javalearn.javabase.thread.atomic.AtomicReferanceTest - persion 2 :AtomicReferanceTest.Persion(name=linda, id=33)