JVM命令启动选项重复

发布于 2024-12-18 22:27:37 字数 224 浏览 7 评论 0原文

我发现我们正在使用的一个遗留软件的启动属性格式错误，因此它接收这两个不相等的 xmx 作为属性：

java -jar myapp.jar -Xmx128m -Xmx512m

我无权访问启动器源代码（无法修改它），所以我请问，这些参数重复有什么影响？我可以就这样离开吗，还是应该担心？将应用哪一种？

使用的 JVM 是 JRE 6 update 18

原文

I have found a legacy software that we're using that has its launch properties malformed, so it receives these two unequal xmx as a properties:

java -jar myapp.jar -Xmx128m -Xmx512m

I do not have access to the launcher source code(not being able to modify it), so I ask, what is the impact of the duplication of these parameters? Can I leave this in this way, or should I worry? Which one will be applied?

The JVM used is JRE 6 update 18

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审判长 2024-12-25 22:27:37

一般来说，如果工具不拒绝重复项，通常会使用后一个选项，但除非该工具记录它，否则您不能指望这一点。

最好的办法是通过 Runtime 的 totalMemory 和 maxMemory< /a>：

public class HeapSize {
    public static final void main(String[] args) {
        Runtime rt = Runtime.getRuntime();
        System.out.println("Total currently: " + rt.totalMemory());
        System.out.println("Max:             " + rt.maxMemory());
        System.exit(0);
    }
}

在我的 JVM（Linux 下的 Sun/Oracle 1.6.0_26-b03）上，后一个选项生效：

$ java -Xmx16m HeapSize
Total currently: 16121856
Max:             16121856
$ java -Xmx32m HeapSize
Total currently: 32178176
Max:             32178176
$ java -Xmx16m -Xmx32m HeapSize
Total currently: 32178176
Max:             32178176
$ java -Xmx16m -Xmx32m -Xmx128m HeapSize
Total currently: 59113472
Max:             119341056

In general, it's usually the latter option that gets used if a tool doesn't reject a duplicate, but you can't count on that unless the tool documents it.

Your best bet is to see what happens with your specific JVM, via Runtime's totalMemory and maxMemory:

public class HeapSize {
    public static final void main(String[] args) {
        Runtime rt = Runtime.getRuntime();
        System.out.println("Total currently: " + rt.totalMemory());
        System.out.println("Max:             " + rt.maxMemory());
        System.exit(0);
    }
}

On my JVM (Sun/Oracle 1.6.0_26-b03 under Linux), the latter option takes effect:

$ java -Xmx16m HeapSize
Total currently: 16121856
Max:             16121856
$ java -Xmx32m HeapSize
Total currently: 32178176
Max:             32178176
$ java -Xmx16m -Xmx32m HeapSize
Total currently: 32178176
Max:             32178176
$ java -Xmx16m -Xmx32m -Xmx128m HeapSize
Total currently: 59113472
Max:             119341056

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