Weldon Washburn wrote:
Everyone,
I just posted the basics of the GC/VM interface to
http://wiki.apache.org/harmony/HarmonyArchitecture. The VM calls into
the GC using gc_interface.txt. The GC calls into the VM using
vm_gc_interface.txt.
Weldon
Thanks Weldon, it makes very interesting reading. I've posted a
description of MMTk's VM interface on my web page,
http://cs.anu.edu.au/people/Robin.Garner/, for comparison. This is the
GC -> VM interface.
As described in my thesis (although if you want to read it, remember it
is now nearly 2 years out of date, and MMTk has moved on - link is also
on my ANU web page), we follow a "wedge" model of the interface, rather
than specifying a simple flat API. So while JikesRVM (and Rotor and
JNode) have a definite API that they code to, there is a package that
translates this to fit the services MMTk offers. And that's a large
set, not yet documented (beyond source and javadoc in any case).
I'm going to look more closely at the interface you've posted, and will
probably have more questions in a short while, but my first
impressions/questions are:
- The interface seems tightly coupled to ORP and Sapphire. For example,
since there aren't any API calls to do it, I presume the GC knows how
the object header is laid out ? And knows about something called a
vtable ?
- It's not explicitly specified in the API, but I assume gc_alloc_fast
is inlined (or is a macro) ?
- Doesn't supporting gc_pin_object restrict the GC implementation
significantly ?
- I was under the impression ORP doesn't yet support weak references or
finalizers. There appears to be support for the GC to tell the VM about
reference types, but not the other way round. Is this right ? Or is
this the gc_add_weak_root_set_entry call ?
- How does the VM enumerate the thread stacks ? Is this the
gc_add_root_set_entry call ?
Do you have any documentation specifying what else the GC talks to ?
I'm assuming that for its own synchronization, interfacing with the OS
(mmap etc) it talks directly with the OS, glibc etc.
Cheers,
Robin
