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

问题描述

假设我有这个课程:

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

可以一个线程写入这些字段，另一个线程读取它们，而不需要 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处理，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:

澄清一下，这些字段是可变的；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，您需要使它们 final、volatile 或读取 and使用 synchronzied 编写它们以保证阅读器将读取最新的值.正如您现在所拥有的，如果一个线程写入一个值，则不能保证另一个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.多核 CPU 和不同级别的缓存更有可能出现这种情况.

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.

Java 并发实践是一本很好的书.

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