标签：实现 alt 解决 [] thread span pack logs static
一、ThreadLocal
使用wait/notify方式实现的线程安全，性能将受到很大影响。解决方案是用空间换时间，不用锁也能实现线程安全。
来看一个小例子，在线程内的set、get就是threadLocal
package thread2; public class ConnThreadLocal { public static ThreadLocal<String> th = new ThreadLocal<String>(); public void setTh(String value){ th.set(value); } public void getTh(){ System.out.println(Thread.currentThread().getName() + ":" + this.th.get()); } public static void main(String[] args) throws InterruptedException { final ConnThreadLocal ct = new ConnThreadLocal(); Thread t1 = new Thread(new Runnable() { @Override public void run() { ct.setTh("abc"); ct.getTh(); } }, "t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { try { Thread.sleep(1000); ct.getTh(); } catch (InterruptedException e) { e.printStackTrace(); } } }, "t2"); t1.start(); t2.start(); } }
二、单例和多线程
单例常见的有饥饿模式和懒汉模式，但是这两个模式在多线程情况下是不行的。在多线程中考虑到新能和线程安全的问题一般考虑double check instance 和 static inner class这两种方式实现单例模式。
static inner class方式：
package bhz.base.conn011; public class Singletion { private static class InnerSingletion { private static Singletion single = new Singletion(); } public static Singletion getInstance(){ return InnerSingletion.single; } }
double check instance 方式：
package thread2; public class DubbleSingleton { private static DubbleSingleton ds; public static DubbleSingleton getDs(){ if(ds == null){ synchronized (DubbleSingleton.class) { if(ds == null){ ds = new DubbleSingleton(); } } } return ds; } public static void main(String[] args) { Thread t1 = new Thread(new Runnable() { @Override public void run() { System.out.println(DubbleSingleton.getDs().hashCode()); } },"t1"); Thread t2 = new Thread(new Runnable() { @Override public void run() { System.out.println(DubbleSingleton.getDs().hashCode()); } },"t2"); Thread t3 = new Thread(new Runnable() { @Override public void run() { System.out.println(DubbleSingleton.getDs().hashCode()); } },"t3"); t1.start(); t2.start(); t3.start(); } }
标签：实现 alt 解决 [] thread span pack logs static
原文地址：http://www.cnblogs.com/code-java/p/6893207.html
