Re: [Qemu-devel] [PATCH] qom: Use atomics for object refcounting

[Paolo Bonzini <pbonzini@redhat.com>]

Il 02/07/2013 16:47, Anthony Liguori ha scritto:
> Jan Kiszka <jan.kiszka@siemens.com> writes:
> 
>> Objects can soon be referenced/dereference outside the BQL. So we need
>> to use atomics in object_ref/unref.
>>
>> Based on patch by Liu Ping Fan.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>  qom/object.c |    5 ++---
>>  1 files changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/qom/object.c b/qom/object.c
>> index 803b94b..a76a30b 100644
>> --- a/qom/object.c
>> +++ b/qom/object.c
>> @@ -683,16 +683,15 @@ GSList *object_class_get_list(const char *implements_type,
>>  
>>  void object_ref(Object *obj)
>>  {
>> -    obj->ref++;
>> +     __sync_fetch_and_add(&obj->ref, 1);
>>  }
>>  
>>  void object_unref(Object *obj)
>>  {
>>      g_assert(obj->ref > 0);
>> -    obj->ref--;
>>  
>>      /* parent always holds a reference to its children */
>> -    if (obj->ref == 0) {
>> +    if (__sync_sub_and_fetch(&obj->ref, 1) == 0) {
>>          object_finalize(obj);
>>      }
>>  }
> 
> Should we introduce something akin to kref now that referencing counting
> has gotten fancy?

I'm not a big fan of kref (it seems _too_ thin a wrapper to me, i.e. it
doesn't really wrap enough to be useful), but I wouldn't oppose it if
someone else does it.

Paolo