Incrementing the Xmx option to launch a JVM

Question

I'm developing an application launcher (creating an exe using JNI from C++) to launch a Java application. As it is a memory extensive app I need to have 1G of maximum heap space. I'm setting the JavaVMOption -Xmx1024M but is going to fail to allocate that much memory.
I'm using the solution proposed in [http://forum.java.sun.com/thread.jspa?threadID=5220601|http://forum.java.sun.com/thread.jspa?threadID=5220601] and it will give me 866M as result (that won't work either unless I increment the MaxPerm to 100 instead of 64).
The question is mainly: how can I increment the heap space allocated for the application to 1024M since it works from calling java -Xmx1024M from command line?
I'm using a Windows environment with 2G in RAM.
Thanks

Answer 1

Two thoughts.
First as the referenced thread in the last response indicates the VM will only allocate as much contigous space as available. That suggests your application is starting in the middle of the addressable memory. I believe that is adjustable as a link parameter.
Second the Sun source code is available so you could get a copy of that and see how they launch the VM. You might even check the license because at least some of that should be public domain now so if it is the correct part you could just use that directly.