Re: [Vala] Locking null references

["Andrés G. Aragoneses" <knocte gmail com>]

Hi Jürg:

El 30/03/10 11:35, Jürg Billeter escribió:
> Hi Jim,
>
> On Mon, 2010-03-29 at 18:30 -0700, Jim Nelson wrote:
> > In Vala, I can lock a null reference.  Is this by design or a side-effect?
>
> It's by design (constrained by GObject). Unlike in C#/.NET, we don't
> have a monitor available in every object. Due to this constraint, we've

AFAIK, it's not that there's a Monitor available in every object. The
lock statement is translated into a Monitor.Enter() call, but note that
this is a static function call.


> decided to use different lock statement semantics compared to C#. The
> only other option would have been to not support lock statements at
> all .

Well, I'm wondering about a 3rd option which would be a compromise: that
vala translate every lock statement with a minimal null-check first, so
if the condition is not met, an exception is raised? What do you think
about this approach?


> In Vala lock(foo) locks the field `foo' and not the instance where `foo`
> points to. This means that the current value of the field is completely
> irrelevant, and locking a field whose value happens to be null is
> perfectly fine.
>
> > I think this is fine and should be the documented behavior.  Because Vala
> > only allows locking member variables (and not "this"), being unable to lock
> > a nulled reference would require allocating a dummy object to lock against
> > or explicitly using a Mutex and forgoing lock().  I find both unappealing.
>
> Yes, it's unfortunate that we can't properly support lock(this) as
> GObject doesn't support it and we can't just add a mutex field to
> instance structs as this would result in issues when using lock(this) in
> subclasses. Otherwise, I'd probably recommend using lock(this) in most
> cases.
>
> Jürg