java - Java中原语的同时更新

Question

我正在解决多线程环境中答案的某些下限的迭代计算问题。

在计算过程中，可能会有多个线程尝试更新公共(public)基元变量。对我来说，其中哪一个会成功地写出它的值(value)，哪一个会失败并不重要。

我担心的唯一问题是，是否有可能其中一个线程会写入原语的一部分(例如第一个字节)，而另一个线程会写入另一部分(例如最后一个字节)，因此该线程的值原语将不是线程试图写入的内容。

非常感谢官方文献的链接。

提前致谢。

Answer 1

The only problem I'm bothered about is if it possible that one of the threads would write part of the primitive (e.g. first bytes) and another would write another part (e.g. last bytes) and as a result the value of that primitive would be non of what the threads were trying to write.

引用Java Language Specification :

If a double or long variable is not declared volatile, then for the purposes of load, store, read, and write actions they are treated as if they were two variables of 32 bits each: wherever the rules require one of these actions, two such actions are performed, one for each 32-bit half. The manner in which the 64 bits of a double or long variable are encoded into two 32-bit quantities is implementation-dependent. The load, store, read, and write actions on volatile variables are atomic, even if the type of the variable is double or long.

写入其他原语始终是原子的。但是，如果它们未声明为 volatile ，则更新可能在任意长时间内对其他线程不可见。