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Date: Fri, 8 Sep 2006 09:15:42 -0700
From: "Weldon Washburn" <weldonwjw@gmail.com>
To: harmony-dev@incubator.apache.org
Subject: Re: [DRLVM][JIT] can Jitrino.JET call MMTk alloc() instead of C
 helper?
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On 9/8/06, Mikhail Fursov <mike.fursov@gmail.com> 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:


/**

* 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?
>
> +The test in the patch throws NullPointerException because no memory is
> allocated in alloc() now and JET tries to write vtable data by NULL
> address.
>
>
>
> On 9/7/06, Weldon Washburn <weldonwjw@gmail.com> wrote:
> >
> > At some point soon we need to go multithread.  When can you fix the
> > vmmagic
> > atomic operations?
> >
>
> I need one more day to estimate the complexity of this move.
>
>
> --
> Mikhail Fursov
>
>


-- 
Weldon Washburn
Intel Middleware Products Division

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