ExecutorService的线程安全静态初始化 [英] Threadsafe static initialization of ExecutorService

问题描述

我试图基于按需初始化"持有人惯用语创建一个线程安全的单例类.这是我的代码

I am trying to create a threadsafe singleton class based on Initialization-on-demand holder idiom . Here is my code

public class Check{ 
  private Check(){  }
  private static class Provider {
    static final ExecutorService INSTANCE = new ThreadPoolExecutor(5, "read this val from file", 60L, TimeUnit.SECONDS, new LinkedBlockingQueue());
  }
  public static ExecutorService getInstance() {
    return Provider.INSTANCE;
  }
}

我的期望是以线程安全的方式初始化ExecutorService，并且那里只有一个实例(静态).

My expectation is to initialize ExecutorService in a threadsafe manner and only one instance should be there (static).

此代码是否达到了目标-还是需要任何更改?

Is this code achieving that - or are any changes required?

推荐答案

根据SEI

According to the SEI guidelines your approach is fine.

但是由于我们有枚举，因此可以使用枚举的简单方法:

But since we have enums, the easy way to get that to use enums:

public enum Service {
  INSTANCE;

  private final ExecutorService service = ...
  public getService() { return service ; }

如果您想变得真正聪明，还可以定义一个枚举实现的接口；因为这样您以后可以模拟使用该单例.这对于使用相同线程执行服务替换编写单元测试非常有帮助.

And if you want to be really smart, you also define an interface which that enum implements; because that allows you to later mock usages of that singleton. Which becomes extremely helpful for writing unit tests using a same-thread-exectution-service replacement.

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