在Java中遇到的最常见的并发问题是什么？ [英] What is the most frequent concurrency issue you've encountered in Java?

问题描述

这是Java中常见并发问题的一种轮询。一个例子可能是经典的死锁或竞态条件，或者可能是Swing中的EDT线程错误。我对广泛的可能问题感兴趣，但也在最常见的问题。因此，请留下每个注释的Java并发错误的一个具体答案，如果看到您遇到的错误，请投票。

This is a poll of sorts about common concurrency problems in Java. An example might be the classic deadlock or race condition or perhaps EDT threading bugs in Swing. I'm interested both in a breadth of possible issues but also in what issues are most common. So, please leave one specific answer of a Java concurrency bug per comment and vote up if you see one you've encountered.

推荐答案

我看到的最常见的并发问题是，没有意识到一个线程写入的字段不能保证被另一个线程看到。这是一个常见的应用：

The most common concurrency problem I've seen, is not realizing that a field written by one thread is not guaranteed to be seen by a different thread. A common application of this:

class MyThread extends Thread {
  private boolean stop = false;

  public void run() {
    while(!stop) {
      doSomeWork();
    }
  }

  public void setStop() {
    this.stop = true;
  }
}

只要停止不是或 setStop 和运行不会同步，这不能保证工作。这个错误尤其糟糕，因为在99.999％在实践中没有关系，因为读者线程最终会看到改变 - 但我们不知道他多久看到它。

As long as stop is not volatile or setStop and run are not synchronized this is not guaranteed to work. This mistake is especially devilish as in 99.999% it won't matter in practice as the reader thread will eventually see the change - but we don't know how soon he saw it.

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