如何禁用编译器和 JVM 优化? [英] How to disable compiler and JVM optimizations?

问题描述

我有这段代码正在测试 Calendar.getInstance().getTimeInMillis() 与 System.currentTimeMilli() :

I have this code that is testing Calendar.getInstance().getTimeInMillis() vs System.currentTimeMilli() :

long before = getTimeInMilli();
for (int i = 0; i < TIMES_TO_ITERATE; i++)
{
  long before1 = getTimeInMilli();
  doSomeReallyHardWork();
  long after1 = getTimeInMilli();
}
long after = getTimeInMilli();
System.out.println(getClass().getSimpleName() + " total is " + (after - before));

我想确保没有 JVM 或编译器优化发生，所以测试将是有效的并且会实际显示差异.

I want to make sure no JVM or compiler optimization happens, so the test will be valid and will actually show the difference.

如何确定?

EDIT:我更改了代码示例，使其更加清晰.我在这里检查的是在不同的实现中调用 getTimeInMilli() 需要多少时间 - Calendar vs System.

EDIT: I changed the code example so it will be more clear. What I am checking here is how much time it takes to call getTimeInMilli() in different implementations - Calendar vs System.

推荐答案

我认为您需要禁用 JIT.添加到您的运行命令下一个选项:

I think you need to disable JIT. Add to your run command next option:

-Djava.compiler=NONE

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