Re: Garbage collection durint pcall.

[Andrew Gierth <andrew@...>]

>>>>> "Roberto" == Roberto Ierusalimschy <roberto@inf.puc-rio.br> writes:

 >> This may be totally kosher given the right definition. An object is
 >> dead whenever nobody uses it again, and can be collected at any time
 >> after that.
 >> 
 >> But this definition opens a can of worms for the optimizer. If I do
 >> a=collectable;.......lot of things....;a=a; the optimizer cannot
 >> optimize away the a=a stuff, because that object liveness definition
 >> changes the semantics of a=a, and of all reads of vars in general.

 Roberto> I see the problem the other way around. It is not optimization
 Roberto> that should be restricted; what should be restricted are the
 Roberto> assumptions around finalizers. Of course any optimizer should
 Roberto> be able to erase 'a=a' (as long as the assignment itself has
 Roberto> no side effects, as it can have in C++), as it should be able
 Roberto> to erase any code that does not produce side effects.

But even in the absence of finalizers, holding a (strong) reference to
an object has a visible effect: it prevents the object from vanishing
from a weak table due to collection. So the actual lifetime of a local
variable matters, even if its value is never fetched.

-- 
Andrew.