Re: How to defer userdata memory from being freed?

[Thiago Padilha <tpadilha84@...>]

> If I understand what you're saying; Lua is blind to the fact that B has a reference to A

Yes

> that should prevent A from being garbage collected

I still want the __gc metamethod associated with "A" to be called so I know when there are no references to it other than "B", but I need to stop lua from freeing "A" memory until "B" has completely removed "A" reference(Assume that "B" is a collection of objects of type "A")

> You could create a table entry somewhere that has B as a (weak) key and A as the value.  In function "C", remove the table entry.  So long as B exists then so does A, because of the table entry you created.  If either C is called or B itself is garbage collected, then the table row is removed and A becomes eligible for garbage collection.

I'm more interested in deferring "A" garbage collection. For this problem, we can even assume that "B" is never garbage collected.

On Thu, Nov 19, 2015 at 1:46 PM Peter Pimley <peter.pimley@gmail.com> wrote:

If I understand what you're saying; Lua is blind to the fact that B has a reference to A that should prevent A from being garbage collected.

You could create a table entry somewhere that has B as a (weak) key and A as the value.  In function "C", remove the table entry.  So long as B exists then so does A, because of the table entry you created.  If either C is called or B itself is garbage collected, then the table row is removed and A becomes eligible for garbage collection.

On 19 November 2015 at 14:28, Thiago Padilha <tpadilha84@gmail.com> wrote:

Consider the following scenario:

I have a userdata "A" being referenced referenced by another userdata "B". "A" has the __gc metamethod that can be used to schedule its removal from "B", but note that the reference is not removed immediately, it is deferred until a certain function "C" is called(This is how the library I'm working with behaves). The problem is that if Lua frees "A" memory before "C" is called, "B" will be left with a dangling pointer that can cause memory errors when "C" is called later(It will be called for sure).

What I want to achieve is to defer "A" memory from being freed until C is called. Is there a way to do this? I know that one option is to work with userdata that simply references "A" and take care of freeing memory myself, but I'd rather avoid this because it would need a lot of refactoring in the project I'm working on.