android 处理程序线程安全吗? [英] Are android handlers thread safe?

问题描述

我正在重构一个 Android 项目.我偶然发现了一段我认为非线程安全的奇怪代码.我认为这个例子会导致随机崩溃是否正确?

I am doing some refactoring into an Android project. I have stumble upon a strange piece of code that I consider non thread-safe. Am I correct to think that this example could cause a random crash?

public class SampleClass
{
    Object foo = new Object();

    // foo can be set to null in the main thread

    private Handler handler = new Handler()
    {
        public void handleMessage(Message msg)
        {
            if (foo == null)
                return;

            Thread.sleep(600,0);

            // There is a chance foo has been set to null while the thread was asleep...
            foo.doSomething();
        }
    }
}

尽管我听说处理程序在默认情况下是线程安全的，但似乎我需要在 handleMessage 函数内以及任何可以将 foo 设置为 null 的地方放置同步块.

Even though I hear that handler are thread safe by default, it seems that I would need to place synchronized blocks inside the handleMessage function and any place where foo could be set to null.

推荐答案

Looper 只有在线程处于唤醒状态时才能将 Message 传递给处理程序.'foo' 是一个私有字段，如果你只从那个方法访问它 - 那很好

Looper can deliver Message to handler only when thread is awake. 'foo' is a private field, and if you access it only from that method - that is fine

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