Name: krC82822 Date: 02/17/2001


17 Feb 2001, eval1127@eng -- see also # 4187333.

java version "1.3.0"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.0)
Java HotSpot(TM) Client VM (build 1.3.0, mixed mode)

The java runtime right now is pretty inefficient when it comes to
having multiple runtimes.

You can take the smallest class, run it, and it will take up
X megs of RAM. And the next JVM running it will take up another X megs.
and a third JVM will take up another X megs.
[trivial little program follows below.]

I'm happy to see that 'X' has decreased, from 12 megs for JDK1.2, to
about 6 megs for JDK1.3
But in principle, I would think it could be better still.

If you want java programs to be used as commonly as C programs,
you need to make the runtime similarly efficient about sharing common objects.

One of the reasons C is so memory-efficient is that it has a shared
"libc". The java runtime seems to lack that. I don't think the
common system classes are being shared at all. I guess they're
all being loaded in from "rt.jar" separately.

What the runtime needs is a pre-expanded set of instances of the
standard classes, that can be shared in a .so with additional runtimes.
[Or something similar anyway. Hopefully, you guys can think of something that
 would deliver a similar level of memory sharing]

Here's a trivial class to demonstrate the problem:

public class test {
        public static void main(String args[]){
                System.out.println("Sleeping...");
                try {
                Thread.sleep(10000);
                } catch(Exception err){ }
                System.out.println("Done");
        }
}


Each invocation in parallel, takes the same amount of additional memory as the
initial jvm invocation does.
6 megs each time, for a 542-byte class that doesnt even attempt to open a
graphics window.

This kind of memory footprint makes it impractical to write small java
utilities. If everyone on a system were to use them, they would quickly swallow
available RAM.
(Review ID: 117186)
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