JNI & pointer games in Java

Question

The problem:
I'm malloc'ing a chunk off the stack and returning an int64 with the pointer value into Java. I need to be able to read and write segments of this malloc'ed region from Java without jumping into native functions constantly. Is there a way to root around in this block from within Java? Or would it be better to pull values out of the JVM instead of an intermediate block of memory?
The situation:
I'm working on extending a program that reads DLLs and creates dictionaries of class definitions. Member variables are tracked from the core by a root pointer and a memory offset. struct s {int a; int b;} would be defined in the core with the variables {{"a", enum_int, 0}, {"b", enum_int, 4}}, assuming 32b ints. This model probably wouldn't work to well when applied to objects within the JVM, and I doubt that reaching straight into a JVM's stack and reading values with pointer arithmatic is particularly safe, either. The practical alternative is to hand Java a block of native malloc'ed memory, but then Java needs to be able to pull values out of an arbitrarily organized block.
The macro for defining those member offsets in C is "#define PADDR(X) ((char*)&(this->X)-(char*)this)", to give some perspective.
-Matt

Answer 1

Is there a way to root around in this block from within Java?As stated no.
There is a memory locked JNI api (go look it up). You would map that to a char array then access it that way.
Memory locking has implications for gc so it is usually suggested that you create the space at program start up and not re-allloc while running. Or otherwise don't keep it for very long.
be able to pull values out of an arbitrarily organized block.Memory mapping is only going to work on a contigous block.