Re: [Sablevm-developer] acquiring monitor

[David P. B. <db...@CS...>]

On Sun, Feb 09, 2003 at 02:43:06PM -0800, Archie Cobbs wrote:
> David Paul BELANGER wrote:
> > In the reflection methods already implemented such as
> > nativeGetMethod() (file: java_lang_Class.c), a global monitor is
> > acquired.
> >=20
> > boolean monitor_acquired =3D JNI_FALSE;
> >=20
> > if (_svmf_enter_object_monitor
> >     (env,
> >     *(vm->class_loading.boot_loader.classes.virtualmachine->
> >    class_instance)) !=3D JNI_OK)
> > 					     =20
> > The create/link class methods acquire the same monitor and gc allocat=
ed
> > function seem to have a global mutex.  I don't quite see the reason o=
f
> > acquiring that monitor.  Is it needed for correctness (protecting
> > concurrent access to a function I overlooked or create/link/initializ=
e
> > needs to be done as a block) or is it to avoid
> > acquiring/releasing the monitor several times (link_class,
> > create_class) i.e. for efficiency as acquiring a lock already own is
> > faster?
>=20
> As I understand things, the VirtualMachine monitor is used to
> protect the internal java type data structures.
>=20
> In the case of Class.getMethod() (and therefore Class.nativeGetMethod()=
)
> the spec says that accessing the Method object associated with a
> class is an "active use" and so the class must be linked if it hasn't
> already been linked. And linking the class's type of course requires
> acquiring the monitor.
>=20

Yes, I do understand that part but the link functions do acquire it.
I am wondering why we have this structure:

acquire monitor
.
.
.
link_class()
  (inside link_class)
  acquire monitor
  .
  .
  .
  release monitor
.
initialize_class
  acquire monitor
  .
  .
  release monitor
.
.
release monitor


What functions are we protecting with the external acquire monitor?

Thanks,
David


> -Archie
>=20
> _______________________________________________________________________=
___
> Archie Cobbs     *     Packet Design     *     http://www.packetdesign.=
com

--=20

---

David B=E9langer
Graduate Student
School of Computer Science
McGill University
Office: MC226

Web page:   http://www.cs.mcgill.ca/~dbelan2/
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