CODEWITHSUNDEEP
javajvmheap-memory
Amaresh
Amaresh

Reputation: 341

How to limit JVM creation?

I have created following class and ran on 15 terminals with command "java -Xms500m Class1".

I was expecting it to not allow me after 4 or 5 separate executions. I was expecting something like cannot create more JVMs but all programs are running. If each JVM creation requires 500Mb of initial heap memory (my RAM is 2GB) then the maximum limit of JVM creation should be four. 

public class Class1
{
public static void main(String[] args)
{
  int i=0;
  while(true)
   {
    try
   {
    Thread.currentThread().sleep(100);
    System.out.println("hi-"+i);
   }
   catch (InterruptedException e)
   {
   }
   i++;
   if(i == 1000000)
   {
    break;
   }
 }
}

Thanks, Amaresh

Upvotes: 4

Views: 2507

Answers (3)

Alvin
Alvin

Reputation: 10458

You are able to create JVMs with accumulative heap size bigger than your physical memory because of virtual memory.

In both Unix and Windows, because hard drive are used as memory, you can create 4GB + sizeof(hard drive space assigned to be used as memory) JVMs. So if you have 4GB of RAM and you assigned 2G of your hard drive to be used as memory, you can create 12 JVMs using java -Xmx500 -Xms500.

In Linux the swap space is use as memory. In windows the disk amount to be used as memory can be configured at System Properties->Advanced->Performance->Settings

Upvotes: 2

Chip
Chip

Reputation: 3316

Try using -Xms500m as well. That will set the initial memory.

You were setting the "maximum" memory - but your code doesn't use much memory at all.

Your OS probably also has virtual memory, so it will go a little more than 2GB.

Also, remember that the 500m is the heap size. The actual JVM will take a little more memory than the heap alone.

Upvotes: 1

michael667
michael667

Reputation: 3260

-Xmx is the maximum heap size, -Xms is the initial heap size. See here for more information about setting the heap size correctly.

Upvotes: 4

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