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Re: [Qemu-devel] [PATCH 03/13] qom: add support for weak referenced obje


From: Igor Mammedov
Subject: Re: [Qemu-devel] [PATCH 03/13] qom: add support for weak referenced object: aka UnownedObject
Date: Wed, 28 Jan 2015 13:55:44 +0100

On Wed, 28 Jan 2015 11:09:22 +0100
Paolo Bonzini <address@hidden> wrote:

> 
> 
> On 28/01/2015 11:03, Igor Mammedov wrote:
> > it adds support for weak reference model used by glib's
> > GInitiallyUnowned to QEMU's QOM model.
> > 
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> >  include/qom/object.h | 20 ++++++++++++++++++++
> >  qom/object.c         | 20 +++++++++++++++++++-
> >  2 files changed, 39 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/qom/object.h b/include/qom/object.h
> > index 89c3092..e0e4cc8 100644
> > --- a/include/qom/object.h
> > +++ b/include/qom/object.h
> > @@ -1314,5 +1314,25 @@ int object_child_foreach(Object *obj, int 
> > (*fn)(Object *child, void *opaque),
> >   */
> >  Object *container_get(Object *root, const char *path);
> >  
> > +#define TYPE_UNOWNED_OBJECT "unowned-object"
> > +#define UNOWNED_OBJECT(obj) \
> > +     OBJECT_CHECK(UnownedObject, (obj), TYPE_UNOWNED_OBJECT)
> > +#define UNOWNED_OBJECT_CLASS(klass) \
> > +     OBJECT_CLASS_CHECK(UnownedObjectClass, (klass), TYPE_UNOWNED_OBJECT)
> > +#define UNOWNED_OBJECT_GET_CLASS \
> > +     OBJECT_GET_CLASS(UnownedObjectClass, (obj), TYPE_UNOWNED_OBJECT)
> > +#define OBJECT_WEAK_REF (1UL << 31)
> > +
> > +typedef struct UnownedObjectClass
> > +{
> > +    /*< private >*/
> > +    ObjectClass parent_class;
> > +} UnownedObjectClass;
> > +
> > +typedef struct UnownedObject
> > +{
> > +    /*< private >*/
> > +    Object parent_obj;
> > +} UnownedObject;
> >  
> >  #endif
> > diff --git a/qom/object.c b/qom/object.c
> > index 1812c73..96842c7 100644
> > --- a/qom/object.c
> > +++ b/qom/object.c
> > @@ -705,6 +705,10 @@ void object_ref(Object *obj)
> >      if (!obj) {
> >          return;
> >      }
> > +    if (atomic_fetch_and(&obj->ref, ~OBJECT_WEAK_REF) & OBJECT_WEAK_REF)
> 
> Please first do a non-atomic test, since this is unlikely to happen but
> atomic_fetch_and is quite expensive (it compiles into a cmpxchg loop).
sure

> 
> Paolo
> 
> > +    {
> > +        return;
> > +    }
> >       atomic_inc(&obj->ref);
> >  }
> >  
> > @@ -713,7 +717,7 @@ void object_unref(Object *obj)
> >      if (!obj) {
> >          return;
> >      }
> > -    g_assert(obj->ref > 0);
> > +    g_assert((obj->ref & ~OBJECT_WEAK_REF) > 0);
> >  
> >      /* parent always holds a reference to its children */
> >      if (atomic_fetch_dec(&obj->ref) == 1) {
> > @@ -1709,6 +1713,12 @@ static void object_instance_init(Object *obj)
> >      object_property_add_str(obj, "type", qdev_get_type, NULL, NULL);
> >  }
> >  
> > +
> > +static void unowned_object_instance_init(Object *obj)
> > +{
> > +    obj->ref |= OBJECT_WEAK_REF;
> > +}
> > +
> >  static void register_types(void)
> >  {
> >      static TypeInfo interface_info = {
> > @@ -1724,8 +1734,16 @@ static void register_types(void)
> >          .abstract = true,
> >      };
> >  
> > +    static TypeInfo unowned_object_info = {
> > +        .name = TYPE_UNOWNED_OBJECT,
> > +        .instance_size = sizeof(UnownedObject),
> > +        .instance_init = unowned_object_instance_init,
> > +        .abstract = true,
> > +    };
> > +
> >      type_interface = type_register_internal(&interface_info);
> >      type_register_internal(&object_info);
> > +    type_register_internal(&unowned_object_info);
> >  }
> >  
> >  type_init(register_types)
> > 




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