Re: forcing userdata to be gc'd?

[William Ahern <william@...>]

On Thu, Mar 30, 2017 at 09:34:03AM +0200, Francisco Olarte wrote:
> John:
> 
> On Wed, Mar 29, 2017 at 10:51 PM, John Dunn <John.Dunn@qsc.com> wrote:
> > It seems like a way to tag something to always be garbage collected as soon as there are no longer any references might work.
> 
> This idea is it needs two parts. One to detect the "as soon as there
> are no longer any references" plus another to "tag something to..." (
> and implement the special collections for this ). If you have the
> first one, why bother with the second, just _gc it instead of tagging.
> 
> Reference counting is something which must either be built deeply into
> the language ( like perl or C-python ) or be implemented in a language
> which gives you more control on your data ( like C++, where you can
> mix manually managed, reference counting and garbage-collected data in
> the same program ). I, particularly, would love to have a way to
> choose ( as my objects typically split into two categories, things
> like sockets, db handles, files, which do not participate in cycles (
> or can easily be made not to ) and would like to have managed in a
> release-fast way and memory-chunk-like data which I do not care when
> it is freed. That's why I favour C++ ways, where I manage my heavy
> resources with reference counting and use garbage collectors or memory
> pools ( where you free the whole pool ) for things like graphs.

Either Roberto or Luiz once proposed a construct that automatically invoked
a __close metamethod on an object upon exiting a block. IIRC, it would be
invoked even if scope exit occured because an error was thrown.

I thought that was a cool idea. It's similar to the using, with, and defer
statements of other languages.

I suppose all it would really require is a linked-list, stack-like data
structure adjacent to the jmp_buf structure used for exception handling.
Plus some new opcodes and changes to the code generator. Some of those
changes might be tricky.