I've been trying to find out the details on using Java in 64 bit
mode in Mac OS/X. Is this possible under Java 5? If not is it
going to be possible in Java 6? I suppose what I'm really trying
to find out is if it is possible to heap sizes > 2GB.
Java on Mac OS X depends on frameworks and libraries that don't
provide 64-bit interfaces on 10.4 or earlier however Mac OS X 10.5 is
expanding 64-bit support to all non-deprecated frameworks and
application development environments.
The near two 2 GiB limit you currently see for Java isn't a direct
limit of a 32-bit virtual address space (32-bit yields 4 GiB address
space per process) but is a result of fragmentation of the 32-bit
virtual address space. The fragmentation comes about from reserved
memory ranges and shared library/framework mappings. If the Java heap
was allocated in smaller chunks and not in a large block likely it
could grow to near 3.5 GiB in size (about the maximum amount of
memory available after you subtract out all of the reserved ranges
When dealing with a 64-bit virtual address space the reserved ranges
and mapping will reasonably be a non issue given the immense size of
a 64-bit virtual address space.
p.s. It isn't called "Mac OS/X" but "Mac OS X".
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