这是JVM错误还是“预期行为"? [英] Is this a JVM bug or "expected behavior"?

问题描述

我注意到了一些意外的行为(相对于我的个人期望而言是意外的)，我想知道是否是JVM中存在错误，或者这可能是我不了解某些细节的附带情况到底应该发生什么.假设我们自己在main方法中有以下代码:

I noticed some unexpected behavior (unexpected relative to my personal expectations), and I'm wondering if something if there is a bug in the JVM or if perhaps this is a fringe case where I don't understand some of the details of what exactly is supposed to happen. Suppose we had the following code in a main method by itself:

int i;
int count = 0;
for(i=0; i < Integer.MAX_VALUE; i+=2){
  count++;
}
System.out.println(i++);

幼稚的期望是它将打印Integer.MAX_VALUE-1，最大的甚至可表示的int.但是，我相信整数算术应该在Java中翻转"，因此在Integer.MAX_VALUE中加1应该会导致Integer.MIN_VALUE.由于Integer.MIN_VALUE仍然小于Integer.MAX_VALUE，因此循环将循环遍历负整数.最终它将恢复为0，并且此过程应作为无限循环重复进行.

A naive expectation would be that this would print Integer.MAX_VALUE-1, the largest even representable int. However, I believe integer arithmetic is supposed to "rollover" in Java, so adding 1 to Integer.MAX_VALUE should result in Integer.MIN_VALUE. Since Integer.MIN_VALUE is still less than Integer.MAX_VALUE, the loop would keep iterating through the negative even ints. Eventually it would get back to 0, and this process should repeat as an infinite loop.

当我实际运行此代码时，会得到不确定的结果.打印的结果往往大约为一百万，但是确切的值却有所不同.因此，当我认为循环应该是无限循环时，循环不仅终止了，而且似乎随机终止了.发生了什么事?

When I actually run this code, I get non-deterministic results. The result that gets printed tends to be on the order of half a million, but the exact value varies. So not only is the loop terminating when I believe it should be an infinite loop, but it seems to terminate randomly. What's going on?

我的猜测是，这要么是JVM中的错误，要么是正在进行许多时髦的优化，从而产生了预期的行为.是哪一个?

My guess is that this is either a bug in the JVM, or there is a lot of funky optimization going on that makes this expected behavior. Which is it?

推荐答案

已知错误.与

http://bugs.sun.com/bugdatabase/view_bug.do? bug_id = 6196102

http://bugs.sun.com/bugdatabase/view_bug.do? bug_id = 6357214

和其他人.

我认为它们被认为是低优先级的，因为它们不在现实世界中出现.

I think they're considered low-priority to fix because they don't come up in the real world.

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