Re: [Qemu-devel] [PATCH 06/11] qobject: add QBool type

[Anthony Liguori <aliguori@us.ibm.com>]

Luiz Capitulino wrote:
> On Sat, 17 Oct 2009 08:36:06 -0500
> Anthony Liguori <aliguori@us.ibm.com> wrote:
>
>   
>> We currently model as json bool as an int.  This works fine on the server side
>> but it means we cannot send back proper bools to the client.  Introducing a
>> proper QBool type fixes that.
>>     
>
>  As we talked earlier today, I think it would be simpler to have QTrue,
> QFalse and QNull as static objects.
>
>  We could define that static objects get reference counting disabled, I don't
> see issues in doing that and we get a very simple model.
>
>  The big patch bellow does it, only compiled tested though.
>
>  If you don't agree with this model, we'll have to allocate QNull objects.
> Actually I would suggest a destroy() method which always resets the
> refcount to 1, but then it will have the concurrency problems on threaded
> applications you've mentioned.
>   

A lot of object systems have dealt with this in various ways.  The 
trouble with reference counting is usually thread safety.  CLR goes to 
great lengths to make their objects reference counting thread safe and 
it comes at a cost.  Python doesn't do anything explicit and it's one of 
the reasons that they're stuck with a big lock.

Since I'd like to expose QObject to client libraries, having a single 
static instance would be pretty unfortunate as it would imply a weird 
locking semantics.  Disabling reference counts for QNull/QBool seems 
unfortunate because it suggests that different semantics for certain 
objects.

I think this is a premature optimization.  I don't think we need to try 
and save the memory here.

Regards,

Anthony Liguori