是jvm原子中的所有指令吗? [英] are all instructions in jvm atomic?

问题描述

我记得我以前读过某个地方，但是现在找不到正式文档.

I remember I read the somewhere before,but I can't find the offical document now.

jvm中的所有指令都是原子的吗?

are all instructions in jvm all atomic?

喜欢:

iinc
iload
aload

所有原子?

推荐答案

您提到的字节码指令(iinc，iload，aload等)对操作数堆栈中的值进行操作和局部变量.这些区域是线程局部的(请参阅JVMS 2.5 ， 2.6 )，也就是说，在这里谈论原子性是没有意义的. IE.不能使用lock xadd之类的原子CPU指令来实现它们，但是没有人应该在意.

The bytecode instructions you mentioned (iinc, iload, aload etc.) operate on the values from the operand stack and on the local variables. These areas are thread-local (see JVMS 2.5, 2.6), that is, speaking about atomicity here is meaningless. I.e. they are NOT implemented using atomic CPU instructions like lock xadd, but nobody should care.

读取或写入字段和数组元素(getfield，putfiled，iastore等)的字节码指令是原子的，但long和double类型除外(请参见JLS

The bytecode instructions that read or write fields and array elements (getfield, putfiled, iastore etc.) are atomic except for long and double types (see JLS 17.7). 32-bit JVM may implement (actually, HotSpot JVM does implement) reading and writing of 64-bit fields with two 32-bit loads or stores, unless the field is declared volatile.

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