java os x heap size question

0
votes

I have been looking at JVM heap sizes on os x both in eclipse and intellij and running applications directly through the command line and I'm seeing a weird behavior I am hoping someone can explain.

  1. If I set the jvm heap size to something large (e.g. over 1gb) for eclipse and then run a hello world application that executes

    System.out.println(Runtime.getRuntime().maxMemory());

I see that it has 129957888 (128mb) as max memory.

  1. If I run the same experiment in intellij, I get the same result but the heap size indicator in the bottom corner says I'm only using 100mb out of 2gb that I can.

  2. If I just run java test -Xmx1024mb, then it tells me that I have the right amount max memory. (8 times as much)

I have tried this on 10.6 and 10.7 and I'm seeing the same thing, so I'm wondering what is going on with the IDE's not consuming as much heap size as I want them to. I am getting heap out of space errors when I have gigs of ram on my machines sitting there unused and I am finding this to be ridiculous.

Thanks for any help anyone can provide.

1
macosjvmheap-memory

1 Answers

1
votes

It sounds like you are setting the heap size for the IDE's JVM instead of for the JVMs the IDEs are launching to run your programs. It would be dangerous if an IDE ran your code in the same JVM in which it was running.

In Eclipse, the default heap size used when running programs is 128 MB. You can override this with a run or debug configuration.

  1. Right click on the Java class with the main method you want to run
  2. Select Run As -> Run Configurations...
  3. Click on the Arguments tab
  4. In the VM arguments section, enter -Xmx256m
  5. Click Run

The above setting sets the max heap size used by the JVM to 256 MB.

The output for your test class should now be 265093120.