Weldon Washburn wrote:
On 9/8/06, Mikhail Fursov <[EMAIL PROTECTED]> wrote:
Weldon,
I added 'alloc' support to JIRA 816 (magic2.zip file)
Now it supports objects allocation only, not arrays. MMTk allocation
works
only for class named 'test' and methods with prefix 'testAlloc'. To
turn
it on use "-Xjit jet::alloc4j" option.
Thanks! I will take a look this weekend.
I had a problem with implementation: usual 'new' vm helper does vtable
field
initialization in allocated object space by itself. Your alloc() method
doesn't.
In the patch in JIRA I added vtable initialization code right after the
alloc() call to JIT, that is actually bad design decision (IMO).
You are correct. Its bad design. Writing the vtable pointer is not the
responsibility of the JIT. MMTk is somewhat vague on who owns vtable ptr
init. In any case, it looks like the jit should follow the call to alloc()
with a call to postAlloc(). I will make sure the postAlloc() code fixes up
the vtable ptr. Its OK to "bend" the typeRef. All I want is the hard ptr
that gets written into the object header. We will go back later and fix
this interface hack. See below:
Ummm ... MMTk isn't vague on who owns vtable ptr initialization - it's
the responsibility of the VM. MMTk strives to know as little about the
object model as possible, apart from what is exposed through the
ObjectModel interface. OK, perhaps the contract isn't as clearly
expressed as it chould be :)
In JikesRVM, the incoming interface (MM_Interface) provides the
vm-specific features such as adding the object header size to the
allocation request, filling in the non-GC portions of the header etc. I
think that approach would work for DRLVM.
MMTk definitely doesn't want to know about vtables and type pointers -
after all there are plenty of systems it could be built into that don't
have such things.
/**
* Perform post-allocation actions. For many allocators none are
* required.
*
* @param ref The newly allocated object
* @param typeRef the type reference for the instance being created
* @param bytes The size of the space to be allocated (in bytes)
* @param allocator The allocator number to be used for this allocation
*/
public void postAlloc(ObjectReference ref, ObjectReference typeRef,
int bytes, int allocator) throws InlinePragma {
Can we replace the 'alloc()' call with another Java method that uses
unboxed API and behaves exactly like 'new' helper?
I think that's what I'm saying MMTk expects.
cheers
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