2017-05-17 Java并发编程学习2
volatile关键字
volatile可以保证可见性，但是不能保证原子性
volatile的一些场景：
-
状态标记 · public clamo’sss ServerHandler { private volatile isopen; public void run() { if (isopen) { //促销逻辑 } else { //正常逻辑 } } public void setIsopen(boolean isopen) { this.isopen = isopen } } · isopen代表是否促销，一个线程修改了isopen，其他线程都可以得到其最新值。
-
单例模式时懒加载保证线程安全 · class Singleton { private volatile static Singleton instance; public static Singleton getInstance() { if (instance == null) { syschronized(Singleton.class) { if (instance == null) { instance = new Singleton(); } } } return instance; } } ·
懒加载另一个比较好的方式
·
public class Singleton {
static class SingletonHolder {
static Singleton instance = new Singleton();
}
public static Singleton getInstance(){
return SingletonHolder.instance;
} } ·
一个Demo: ` public class Scene {
private static int MY_INT = 0;
public static void main(String[] args) {
new ChangeListener().start();
new ChangeMaker().start();
}
static class ChangeListener extends Thread {
@Override
public void run() {
int local_value = MY_INT;
while ( local_value < 5){
if( local_value!= MY_INT){
System.out.println("Got Change for MY_INT : " + MY_INT);
local_value= MY_INT;
}
}
}
}
static class ChangeMaker extends Thread{
@Override
public void run() {
int local_value = MY_INT;
while (MY_INT <5){
System.out.println("Incrementing MY_INT to " + (local_value+1));
MY_INT = ++local_value;
try {
Thread.sleep(500);
} catch (InterruptedException e) { e.printStackTrace(); }
}
}
}
} `