英文:
Why JVM doesn't throw out of memory error even if the memory reached the maximum heap size?
问题
我正在运行一个Java程序，在while循环内部创建了更多的内存对象。
我将最大堆大小设置为10MB。我在任务管理器中观察，JVM甚至在超过10MB后仍在运行。
我期望出现内存溢出错误。但实际上没有抛出异常，而是在while循环中不断打印一条语句。
**`java -Xmx10m Main`**
public class Main
{
public static void main(String[] args) {
System.out.println("Hello World");
String s1 = "01011001100100";
char[] charArray = s1.toCharArray();
int index = 0;
StringBuffer result = new StringBuffer();
StringBuffer temp = new StringBuffer();
while(index < charArray.length){
System.out.println(index + " : " + charArray[index]);
if(charArray[index] == '1' && charArray[index--] == '0'){ ***--- 这是有问题的代码***
result.append(1);
} else {
temp.append(charArray[index]);
}
index++;
}
System.out.println("Result >" + result);
}
}
英文:
I am running a Java programming which creates more objects in memory inside a while loop.
I set the maximum heap size as 10MB. I am watching task manager, the JVM runs even after 10 MB.
I am expecting out of memory. But it is not throwing , it is keep printing a statement in while loop.
java -Xmx10m Main
public class Main
{
public static void main(String[] args) {
System.out.println("Hello World");
String s1 = "01011001100100";
char[] charArray = s1.toCharArray();
int index = 0;
StringBuffer result = new StringBuffer();
StringBuffer temp = new StringBuffer();
while(index < charArray.length){
System.out.println(index+" : "+charArray[index]);
if(charArray[index] == '1' && charArray[index--] == '0'){ ***--- This is buggy code***
result.append(1);
} else {
temp.append(charArray[index]);
}
index++;
}
System.out.println("Result >"+result);
}
}
Thanks
答案1
得分: 1
因为-xmx参数设置的是Java虚拟机的最大堆大小，而不是Java进程的总内存大小。很多JVM内存的使用并不在堆中，包括：
- 用于保存
java可执行文件和共享本地库的代码的内存 - 用于本地堆的内存，比如本地代码中的
malloc调用 - 用于元空间的内存
- 用于线程栈的内存
- 在将文件映射到内存时使用的内存
- 等等。
上述情况中的一些可能会导致OOME（例如，无法分配新的线程栈），但是使用-xmx设置的堆大小不会以任何方式限制它们。
英文:
> Why JVM doesn't throw out of memory error even if the memory reached the maximum heap size?
Why?
Because the -xmx parameter sets the maximum Java heap size, NOT the total memory size for the Java process. A lot of a JVM's memory utilization is not in the heap. This includes:
- memory used to hold the code for the
javaexecutable and shared native libraries - memory used for the native heap; e.g.
malloccalls in native code - memory used for metaspace
- memory used for thread stacks
- memory used when a file is mapped into memory
- and so on.
Some of the above can lead to an OOME (for example, failure to allocate a new thread stack), but the heap size that you set with -xmx does not limit them in any way.
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