volatile的原理實作可以看 這篇文章 ，真的是從硬體層面上說明了volatile怎樣保證可見性
public class RunThread extends Thread{
private volatile boolean isRunning = true;
private void setRunning(boolean isRunning){
this.isRunning = isRunning;
}
public void run(){
System.out.println("進入run方法..");
int i = 0;
while(isRunning == true){
//..
}
System.out.println("線程停止");
}
public static void main(String[] args) throws InterruptedException {
RunThread rt = new RunThread();
rt.start();
Thread.sleep(1000);
rt.setRunning(false);
System.out.println("isRunning的值已經被設定了false");
}
}
這是展示volatile雖然有可見性，但是沒有原子性：
/**
* volatile關鍵字不具備synchronized關鍵字的原子性（同步）
* @author alienware
*
*/
public class VolatileNoAtomic extends Thread{
private static volatile int count = 0;
//這個被注釋的代碼可以保證結果正确
//private static AtomicInteger count = new AtomicInteger(0);
private static void addCount(){
for (int i = 0; i < 1000; i++) {
count++ ;
//這個被注釋的代碼可以保證結果正确
//count.incrementAndGet();
}
System.out.println(count);
}
public void run(){
addCount();
}
public static void main(String[] args) {
VolatileNoAtomic[] arr = new VolatileNoAtomic[100];
for (int i = 0; i < 10; i++) {
arr[i] = new VolatileNoAtomic();
}
for (int i = 0; i < 10; i++) {
arr[i].start();
}
}
}
這是使用atomic，保證原子性的代碼：
public class AtomicUse {
private static AtomicInteger count = new AtomicInteger(0);
//多個addAndGet在一個方法内是非原子性的，需要加synchronized進行修飾，保證4個addAndGet整體原子性
/**synchronized*/
public synchronized int multiAdd(){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
count.addAndGet(1);
count.addAndGet(2);
count.addAndGet(3);
count.addAndGet(4); //+10
return count.get();
}
public static void main(String[] args) {
final AtomicUse au = new AtomicUse();
List<Thread> ts = new ArrayList<Thread>();
for (int i = 0; i < 100; i++) {
ts.add(new Thread(new Runnable() {
@Override
public void run() {
System.out.println(au.multiAdd());
}
}));
}
for(Thread t : ts){
t.start();
}
}
}
線程通信
ListAdd2.java，可以看出本來list已經到5了，那麼t2應該出while循環抛異常，但是因為它執行了wait方法，釋放鎖了。而t1得到鎖一直執行，雖然t1執行了notify方法，但是隻是發出通知而已，隻有它的方法執行完才釋放鎖讓t2執行。
package com.bjsxt.base.conn008;
import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.LinkedBlockingQueue;
/**
* wait notfiy 方法，wait釋放鎖，notfiy不釋放鎖
* @author alienware
*
*/
public class ListAdd2 {
private volatile static List list = new ArrayList();
public void add(){
list.add("bjsxt");
}
public int size(){
return list.size();
}
public static void main(String[] args) {
final ListAdd2 list2 = new ListAdd2();
// 1 執行個體化出來一個 lock
// 當使用wait 和 notify 的時候 ， 一定要配合着synchronized關鍵字去使用
final Object lock = new Object();
// final CountDownLatch countDownLatch = new CountDownLatch(1);
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
try {
synchronized (lock) {
for(int i = 0; i <10; i++){
list2.add();
System.out.println("目前線程：" + Thread.currentThread().getName() + "添加了一個元素..");
Thread.sleep(500);
if(list2.size() == 5){
System.out.println("已經發出通知..");
// countDownLatch.countDown();
lock.notify();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "t1");
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
synchronized (lock) {
if(list2.size() != 5){
try {
System.out.println("t2進入...");
lock.wait();
// countDownLatch.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("目前線程：" + Thread.currentThread().getName() + "收到通知線程停止..");
throw new RuntimeException();
}
}
}, "t2");
t2.start();
t1.start();
}
}
package com.xushu.multi;
import java.util.LinkedList;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
public class MyQueue {
private LinkedList<Object> list = new LinkedList<Object>();
private AtomicInteger count = new AtomicInteger(0);
private final int minSize = 0;
private final int maxSize;
public MyQueue(int size) {
this.maxSize = size;
}
private final Object lock = new Object();
public void put(Object obj) {
synchronized (lock) {
if (count.get() == this.maxSize) {
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
list.add(obj);
count.incrementAndGet();
lock.notify();
System.out.println("新加入的元素為：" + obj);
}
}
public Object take() {
Object ret = null;
synchronized (lock) {
if (count.get() == minSize) {
try {
lock.wait();
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
ret = list.removeFirst();
count.decrementAndGet();
lock.notify();
}
return ret;
}
public int getSize() {
return this.count.get();
}
public static void main(String[] args) {
final MyQueue mq = new MyQueue(5);
mq.put("a");
mq.put("b");
mq.put("c");
mq.put("d");
System.out.println("目前容器的長度:" + mq.getSize());
Thread t1 = new Thread(new Runnable() {
@Override
public void run() {
mq.put("f");
mq.put("g");
mq.put("e");
}
}, "t1");
t1.start();
Thread t2 = new Thread(new Runnable() {
@Override
public void run() {
Object o1 = mq.take();
System.out.println("移除的元素為:" + o1);
Object o2 = mq.take();
System.out.println("移除的元素為:" + o2);
}
}, "t2");
try {
TimeUnit.SECONDS.sleep(2);
} catch (InterruptedException e) {
e.printStackTrace();
}
t2.start();
}
}