对于Java中的线程安全延迟加载的Singleton，这是否是一个好的实现? [英] Is this a good implementation for a Thread Safe Lazily Loaded Singleton in Java?

问题描述

我想在Java中实现线程安全延迟加载的Singleton.

I want to implement Thread Safe Lazily Loaded Singleton in Java.

这是一个好的设计吗?

public final class ThreadSafeLazySynchronizedSingleton {

private ThreadSafeLazySynchronizedSingleton(){}

private static ThreadSafeLazySynchronizedSingleton instance;

public static ThreadSafeLazySynchronizedSingleton getSynchronizedInstance(){
    synchronized(ThreadSafeLazySynchronizedSingleton.class){ 
        if (instance==null){
            instance = new ThreadSafeLazySynchronizedSingleton();
        }
        return instance;
    }
}

}

我还想创建一个无锁版本，用于一个线程比其他线程访问Singleton多次的情况，我该如何使用Java中的原子对象(即AtomicBoolean或AtomicReference等)来实现此目的.您能提供一个代码示例吗?

I also want to create a lock-less version for use in a scenario where one thread accesses the Singleton many more times than the other threads, how would I achieve this using the atomic objects in Java, ie AtomicBoolean or AtomicReference etc. Could you provide a code example please?

推荐答案

一个更好的设计是

public final class ThreadSafeLazySynchronizedSingleton {

    private ThreadSafeLazySynchronizedSingleton(){}

    private static volatile ThreadSafeLazySynchronizedSingleton instance;

    public static ThreadSafeLazySynchronizedSingleton getSynchronizedInstance(){
        if (instance==null)
            synchronized(ThreadSafeLazySynchronizedSingleton.class){ 
                if (instance==null){
                    instance = new ThreadSafeLazySynchronizedSingleton();
                }
        return instance;
        }
    }
}

但是，最好的恕我直言的设计是

However, the best design IMHO is

public enum ThreadSafeLazySynchronizedSingleton {
    INSTANCE;
}

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