程序怎么可能只包含线程安全类，而不是线程安全类? [英] How is it possible for a program to contain exclusively thread-safe classes, but not be thread-safe?

问题描述

我正在阅读实践中的Java并发性"，作者说:完全由线程安全的类组成的程序可能不是线程安全的".这怎么可能?我似乎不明白，有人可以举个例子吗?

I am reading "java concurrency in practice", and the author says: "A program that consists entirely of thread-safe classes may not be thread-safe". How is this possible? I don't seem to understand, can someone provide an example?

推荐答案

一个示例将是线程安全的类上的单个方法，但如果您调用多个方法，它们不是原子的.例如

An example would be individual methods on a class that are thread safe, but they are not atomic if you invoke more than one. E.g.

if (!threadSafeCollection.contains(thing)) {
  threadSafeCollection.add(thing);
}

如果另一个线程在此线程的contains和add调用之间添加到集合中，则可能会产生错误的结果.

This may yield incorrect results if another thread adds to the collection between the contains and add invocations in this thread.

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