如何在没有实际执行的情况下测试ThreadLocal是否已初始化？ [英] How to test if a ThreadLocal has been initialized without actually doing that?

问题描述

我想测试是否已初始化 ThreadLocal 而未实际初始化它。当然，代码需要是线程安全的。理想情况下我想要这样的东西：

I want to test if a ThreadLocal has been initialized without actually initializing it. Of course, the code needs to be thread-safe. Ideally I want something like this:

class TestableThreadLocal<T> extends ThreadLocal<T> {
    public boolean isInitialized() {
        ...
    }
}

但是我如何实现这个方法呢？

But how would I implement this method?

编辑：动机：我已经子类化了 ThreadLocal 覆盖 initialValue（）。但是，我并不总是需要初始化，特别是因为它可能会导致多类加载器环境中的内存泄漏。一个简单的测试可以帮助我编写代码以避免意外初始化。

Motivation: I have subclassed a ThreadLocal to override initialValue(). However, I do not always need the initialization, in particular because it could cause a memory leak in multi-classloader environments. A simple test would help me write code to avoid the accidental initialization.

推荐答案

我倾向于使用简单的规则来避免类加载器泄漏，诚然，它们很麻烦，但有一些包装并没有那么糟糕。是的，泄密是邪恶的。

I tend to use simple rules to avoid classloader leaks, admittedly they are cumbersome but with some wrapping it's not that bad. Yes, leaks are evil.

• 不覆盖 initialValue ，永远 - 你是只是要求麻烦，只是忘记它存在。


• 除非你做 threadLocal.set（xxx），否则不要在ThreadLocal中存储非系统/非bootstap类; try {... process ...} finally {threadLocal.set（null）;}


• 如果仍然覆盖initialValue，请使用 threadLocal.remove（）不是 threadLocal.set（null）


• 或使用 WeakReferene （即ThreadLocal < WeakReference< Foo>> ），用于保存硬引用的池中的值。它可能看起来很直观但是一旦清除了池，值就会消失，类可以自由地进行GC

• do no override initialValue, ever - you are just asking for trouble, just forget it exists.
• do not store non-system/non-bootstap classes in the ThreadLocal unless you do threadLocal.set(xxx); try{...process...}finally{threadLocal.set(null);}
• if you still override initialValue, use threadLocal.remove() not threadLocal.set(null)
• or use WeakReferene(i.e. ThreadLocal<WeakReference<Foo>>) for the value from a pool that keeps the hard references. It might look counter intuitive but once the pool is cleared the values disappear and the classes are free to be GC'd

我意识到帖子不是对你的问题的直接回复，但是没有简单的方法来达到你想要的目的并防止泄密。

I realize the post is not a direct reply to your question, however there is no simple way to achieve what you wish and keep the leaks at bay.

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