普通单例模式我明白,但是现在希望实现每个线程都有一个唯一的单例,应该怎么做?
我知道用Threadlocal变量可以为每个线程提供一个独立的实例,但是不能保证这个实例是唯一的、不可变得。
如果用volatile修饰的话,按volatile的意义理解就是每个线程都有一份实例的副本,但是这些副本是不是同一个对象呢?
解决方案
class ThreadLocalSingleton { private ThreadLocalSingleton(){} public final static ThreadLocal<ThreadLocalSingleton> INSTANCE = new ThreadLocal<ThreadLocalSingleton>(){ @Override protected ThreadLocalSingleton initialValue(){ return new ThreadLocalSingleton(); } };}public class ThreadLocalSingletonTest{ @Test public void testThreadLocalSingleton() throws InterruptedException{ for(int i=0; i<5; i++){ new Thread(new Runnable(){ @Override public void run() { System.out.println(ThreadLocalSingleton.INSTANCE.get()); } }).start(); } Thread.sleep(3000); }}
结果, 每个thread都对应唯一的不可变的 ThreadLocalSingleton实例:
com.test.loader.ThreadLocalSingleton@7d7c214dcom.test.loader.ThreadLocalSingleton@606e8697com.test.loader.ThreadLocalSingleton@784654f6com.test.loader.ThreadLocalSingleton@5174202acom.test.loader.ThreadLocalSingleton@1eebcf2d