Re: [Vala] Locking null references

[Jürg Billeter <j bitron ch>]

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

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