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Commit 4e0b6e1

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更新CAS
1 parent 543d060 commit 4e0b6e1

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10 files changed

+406
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package com.study.lock.cas.demo;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicStampedReference;
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public class ConcurrentStack {
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AtomicStampedReference<Node> top = new AtomicStampedReference<Node>(null,0);
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public void push(Node node){
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Node oldTop;
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int v;
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do{
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v=top.getStamp();
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oldTop = top.getReference();
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node.next = oldTop;
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}
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while(!top.compareAndSet(oldTop, node,v,v+1));
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// }while(!top.compareAndSet(oldTop, node,top.getStamp(),top.getStamp()+1));
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}
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public Node pop(int time){
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Node newTop;
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Node oldTop;
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int v;
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do{
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v=top.getStamp();
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oldTop = top.getReference();
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if(oldTop == null){
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return null;
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}
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newTop = oldTop.next;
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try {
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if (time != 0) {
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System.out.println(Thread.currentThread() + " 睡一下,预期拿到的数据" + oldTop.item);
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TimeUnit.SECONDS.sleep(time); // 休眠指定的时间
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}
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}
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catch (InterruptedException e) {
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e.printStackTrace();
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}
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}
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while(!top.compareAndSet(oldTop, newTop,v,v+1));
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// }while(!top.compareAndSet(oldTop, newTop,top.getStamp(),top.getStamp()));
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return oldTop;
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}
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public void get(){
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Node node = top.getReference();
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while(node!=null){
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System.out.println(node.item);
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node = node.next;
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}
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}
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}
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package com.javaedge.concurrency.cas.demo;
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/**
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* 存储在栈里面元素 -- 对象
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* @author JavaEdge
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* @date 2019年10月18日
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*/
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public class Node {
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public final String item;
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public Node next;
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public Node(String item) {
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this.item = item;
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}
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@Override
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public String toString() {
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return "item内容:" + this.item;
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}
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}
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package com.javaedge.concurrency.cas.demo;
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import java.util.concurrent.TimeUnit;
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import java.util.concurrent.atomic.AtomicReference;
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/**
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* 实现一个 栈(后进先出)
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*
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* @author JavaEdge
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* @date 2019年10月20日
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*/
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public class Stack {
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/**
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* top cas无锁修改
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*/
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AtomicReference<Node> top = new AtomicReference<>();
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public void push(Node node) { // 入栈
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Node oldTop;
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do {
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oldTop = top.get();
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node.next = oldTop;
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}
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// CAS 替换栈顶
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while (!top.compareAndSet(oldTop, node));
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}
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/**
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* 为了演示ABA效果, 增加一个CAS操作的延时
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*
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* @param time
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* @return
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* @throws InterruptedException
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*/
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public Node pop(int time) throws InterruptedException { // 出栈 -- 取出栈顶
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Node newTop;
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Node oldTop;
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do {
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oldTop = top.get();
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if (oldTop == null) {
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return null;
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}
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newTop = oldTop.next;
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if (time != 0) {
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System.out.println(Thread.currentThread() + " 睡一下,预期拿到的数据" + oldTop.item);
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// 休眠指定的时间
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TimeUnit.SECONDS.sleep(time);
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}
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}
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while (!top.compareAndSet(oldTop, newTop));
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return oldTop;
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}
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}
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package com.study.lock.cas.demo;
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public class Test {
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public static void main(String[] args) throws InterruptedException {
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Stack stack = new Stack();
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stack.push(new Node("B"));
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stack.push(new Node("A"));
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Thread thread1 = new Thread(() -> {
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try {
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System.out.println(Thread.currentThread() + " 拿到数据:" + stack.pop(3));
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// #再继续拿,就会有问题了,理想情况stack出数据应该是 A->C->D->B,实际上ABA问题导致A-B->null
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System.out.println(Thread.currentThread() + " 拿到数据:" + stack.pop(0));
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System.out.println(Thread.currentThread() + " 拿到数据:" + stack.pop(0));
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System.out.println(Thread.currentThread() + " 拿到数据:" + stack.pop(0));
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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thread1.start();
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Thread.sleep(300); // 让线程1先启动
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Thread thread2 = new Thread(() -> {
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Node A = null;
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try {
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A = stack.pop(0);
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System.out.println(Thread.currentThread() + " 拿到数据:" + A);
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stack.push(new Node("D"));
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stack.push(new Node("C"));
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stack.push(A);
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} catch (Exception e) {
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e.printStackTrace();
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}
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});
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thread2.start();
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}
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}
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package com.javaedge.concurrency.example.atomic;
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import java.util.concurrent.atomic.AtomicInteger;
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/**
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* atomic 相关测试代码
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*
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* @author JavaEdge
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* @date 2019年10月20日
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*/
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public class AtomicTest {
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public static void main(String[] args) throws InterruptedException {
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// 自增
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AtomicInteger atomicInteger = new AtomicInteger(0);
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for (int i = 0; i < 2; i++) {
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new Thread(() -> {
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for (int j = 0; j < 10000; j++) {
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atomicInteger.incrementAndGet();
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}
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}).start();
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}
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Thread.sleep(2000L);
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System.out.println(atomicInteger.get());
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}
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}
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package com.javaedge.concurrency.example.atomic;
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import sun.misc.Unsafe;
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import java.io.IOException;
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import java.lang.reflect.Field;
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/**
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* 两个线程,对 i 变量进行递增操作
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*
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* @author JavaEdge
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* @date 2019年10月18日
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*/
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public class LockCASDemo {
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volatile int i = 0;
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private static Unsafe unsafe;
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/**
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*
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* 属性偏移量,用于JVM去定位属性在内存中的地址
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*/
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static long valueOffset;
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static {
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try {
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Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
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theUnsafe.setAccessible(true);
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unsafe = (Unsafe) theUnsafe.get(null);
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// CAS 硬件原语 ---java语言 无法直接改内存。 曲线通过对象及属性的定位方式
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valueOffset = unsafe.objectFieldOffset(LockCASDemo.class.getDeclaredField("i"));
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} catch (Exception e) {
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e.printStackTrace();
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}
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// unsafe =
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}
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public void add() { // 方法栈帧~ 局部变量
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// 无锁编程 -- cas + 自旋锁
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// TODO xx00
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// i++; // 三次操作
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int current;
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int value;
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do {
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current = unsafe.getIntVolatile(this, valueOffset); // 读取当前值
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value = current + 1; // 计算
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} while (!unsafe.compareAndSwapInt(this, valueOffset, current, value));// CAS 底层API
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// if(current == i) {
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// i = value; // 赋值
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// } else {
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// // 值发生变化,修改失败
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// }
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}
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public static void main(String[] args) throws InterruptedException, IOException {
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LockCASDemo ld = new LockCASDemo();
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for (int i = 0; i < 2; i++) { // 2w相加,20000
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new Thread(() -> {
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for (int j = 0; j < 10000; j++) {
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ld.add();
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}
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}).start();
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}
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System.in.read(); // 输入任意键退出
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System.out.println(ld.i);
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}
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}
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package com.javaedge.concurrency.example.atomic;
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import java.util.concurrent.atomic.LongAccumulator;
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import java.util.function.LongBinaryOperator;
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/**
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* LongAdder增强版,处理累加之外,可以自行定义其他计算
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*
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* @author JavaEdge
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* @date 2019年10月18日
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*/
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public class LongAccumulatorDemo {
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public static void main(String[] args) throws InterruptedException {
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LongAccumulator accumulator = new LongAccumulator(new LongBinaryOperator() {
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@Override
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public long applyAsLong(long left, long right) {
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// 返回最大值,这就是自定义的计算
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return left < right ? left : right;
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}
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}, 0);
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// 1000个线程
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for (int i = 0; i < 1000; i++) {
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int finalI = i;
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new Thread(() -> {
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accumulator.accumulate(finalI); // 此处实际就是执行上面定义的操作
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}).start();
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}
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Thread.sleep(2000L);
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System.out.println(accumulator.longValue()); // 打印出结果
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}
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}
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package com.javaedge.concurrency.example.atomic;
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import java.util.concurrent.atomic.AtomicLong;
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import java.util.concurrent.atomic.LongAdder;
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/**
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* 测试用例: 同时运行2秒,检查谁的次数最多
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*
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* @author JavaEdge
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* @date 2019年10月18日
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*/
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public class LongAdderDemo {
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private long count = 0;
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/**
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* 同步代码块的方式
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* @throws InterruptedException
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*/
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public void testSync() throws InterruptedException {
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for (int i = 0; i < 3; i++) {
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new Thread(() -> {
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long starttime = System.currentTimeMillis();
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while (System.currentTimeMillis() - starttime < 2000) { // 运行两秒
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synchronized (this) {
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++count;
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}
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}
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long endtime = System.currentTimeMillis();
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System.out.println("SyncThread spend:" + (endtime - starttime) + "ms" + " v" + count);
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}).start();
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}
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}
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/**
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* Atomic方式
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*/
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private AtomicLong acount = new AtomicLong(0L);
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public void testAtomic() throws InterruptedException {
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for (int i = 0; i < 3; i++) {
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new Thread(() -> {
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long starttime = System.currentTimeMillis();
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while (System.currentTimeMillis() - starttime < 2000) { // 运行两秒
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acount.incrementAndGet(); // acount++;
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}
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long endtime = System.currentTimeMillis();
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System.out.println("AtomicThread spend:" + (endtime - starttime) + "ms" + " v-" + acount.incrementAndGet());
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}).start();
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}
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}
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// LongAdder 方式
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private LongAdder lacount = new LongAdder();
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public void testLongAdder() throws InterruptedException {
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for (int i = 0; i < 3; i++) {
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new Thread(() -> {
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long starttime = System.currentTimeMillis();
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while (System.currentTimeMillis() - starttime < 2000) { // 运行两秒
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lacount.increment();
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}
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long endtime = System.currentTimeMillis();
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System.out.println("LongAdderThread spend:" + (endtime - starttime) + "ms" + " v-" + lacount.sum());
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}).start();
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}
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}
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public static void main(String[] args) throws InterruptedException {
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LongAdderDemo demo = new LongAdderDemo();
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demo.testSync();
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demo.testAtomic();
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demo.testLongAdder();
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}
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}

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