我需要同步对Java中不可变类型的访问吗? [英] Do I need to synchronize access to immutable types in Java?

问题描述

让我说我上了这个课:

class Zoo
{
    protected String bearName;
    protected Double trainerSalary;
    protected Integer monkeyCount;
}

一个线程可以写入这些字段，而另一个线程可以读取它们，而无需synchronized访问Zoo对象吗?

Can one thread write to these fields, and another one read them, without requiring synchronized access to the Zoo object?

注意:这些值可以彼此分开对待，因此在读取monkeyCount时更改trainerSalary并不重要.

Note: these values can be treated separate from one another, so it doesn't matter that the trainerSalary is changed while the monkeyCount is read.

编辑:

请澄清一下，这些字段是可变；只有它们引用的对象是不可变的.

Just to clarify, the fields are mutable; only their referenced objects are immutable.

推荐答案

从技术上讲，您需要将其设置为final，volatile或阅读，并使用synchronzied进行书写，以确保读取器将读取最新值.就像您现在拥有的那样，如果一个线程写入一个值，则不能保证另一线程将读取相同的值.这是因为读取线程可能会看到缓存的值.对于多核CPU和各种级别的缓存，这种可能性更大.

Technically you need to make them final, volatile or read and write them using synchronzied to guarantee that the reader will read the most up-to-date value. As you have it right now, if one thread writes in a value, there's no guarantee that another thread will read the same value. This is because the the reading thread may see a cached valued. This is more likely with multi-core CPUs and various levels of cache.

与此相关的一本好书是 Java并发实践.

A great book on this is Java Concurrency in Practice.

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