当运行时JVM内存不足以分配时会发生什么？ [英] What happens when the JVM runs out of memory to allocate during run time?

问题描述

在考虑了很长时间的通用方法来提出这个问题之后（并且找不到一个问题），我只是想问一个具体的例子：假设我有一台Linux机器，它拥有1 Gb的内存，它可以分配给进程（物理和交换总计1 Gb）。

我有一个标准的Oracle Hotspot机器上安装了JVM版本7。如果在某个特定时刻，有足够的程序运行，这样1 Gb中只有400 Mb是免费的，我在那个时候用以下JVM标志启动Java程序：

  java -Xms256m -Xmx512m -jar myJar.jar 
  

发生了什么？ ：

A。 JVM无法立即启动，因为它会尝试分配所有512 Mb的内存并失败（由于目前没有足够的可用内存）？
$ b $如果JVM启动：

如果在某个时候运行的Java进程将需要超过400 Mb的内存（并且仍然只有400 Mb的内存除了当前的Java进程已经使用的版本之外的其他免费版本），将会发生什么：

B。 Java过程会因OutOfMemroyError失败吗？

C。它会失败并出现一些其他（标准）错误？

D。它是未定义的行为吗？

解决方案

-Xmx只是定义了堆的最大大小。它不能保证有太多的记忆与否。它只能确保堆永远不会超过给定的值。也就是说，选项B）会发生，将引发outOfMemoryError。

After thinking for a long time of a generic way to pose this question (and failing to find one) I'm just going to ask it as a concrete example:

Suppose I have a Linux machine which has 1 Gb of memory which it can allocate to processes (physical and swap totals 1 Gb).

I have a standard Oracle Hotspot JVM version 7 installed on the machine. If at a given moment, there are enough programs running such that only 400 Mb of that 1 Gb are free, and I start a Java program at that moment with the following JVM flags:

java -Xms256m -Xmx512m -jar myJar.jar

what happends? :

A. does the JVM fail to start right away because it will try to allocate all of the 512 Mb of memory and fail (due to the fact that there's not enough available memory at the moment)?

if the JVM starts:

if at some point the running Java process will need more than 400 Mb of memory (and there's still only 400 Mb of memory that's free other than what the current Java process has already used), what will happen:

B. will the Java process fail with an OutOfMemroyError?

C. will it fail with some other (standard) error?

D. is it undefined behavior?

解决方案

-Xmx just defines the maximum size of the heap. It makes no guarantee on wether there is so much memory or not. It only ensures that the heap will never be bigger then the given value. That said, Option B.) will happen, an outOfMemoryError will be thrown.

这篇关于当运行时JVM内存不足以分配时会发生什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！