java并发-带有监视器线程的单例设计

Question

因此我有一个单例类

public final class HandlerCache {
    //the cache maintains a handler per thread 
    private final Map<Thread, Handler> cache = new ConcurrentHashMap<>();

    private final Thread monitor;

    private static final HandlerCache INSTANCE = new HandlerCache();

    private HandlerCache() {
        monitor = new Thread() {
        //periodically monitor cache and close handlers when a thread has died
        }
        monitor.start()
    }

    public static HandlerCache getInstance() {
        return INSTANCE;
    }

    public Handler getHandler() throws Exception {
        final Thread thread = Thread.currentThread();
        Handler handler = cache.get(thread);

        if (!(handler == null))
            return handler;

        handler = HandlerFactory.get(getHandlerFromName(thread.getName()));
        cache.put(thread, handler);
        return handler;
    }

}

我在构造函数完成之前将单例实例泄漏到监视器线程，更好的方法是什么？

使缓存 volatile 可以解决问题吗？

Answer 1

正如 user2677485 所提到的，您应该使用 ThreadLocal 并实现initialValue 方法。另一点是Handler的实现应该实现finalize方法，这样当它被GC回收时，这个方法就会被调用，你可以清理你的资源。

代码可以简化为如下所示:

public class HandlerCache {

   private static final handlers = new ThreadLocal<Handler>() {
        protected Handler initializeValue() {
              return HandlerFactory.get(...);
        }
   };

   public static Handler getHandler() {
        return handlers.get();
   }

}