garbage collection (was Re: gpfree_string within temp_at())

[Dave D. <dde...@es...>]

Ethan Merritt <merritt@u.washington.edu> writes:

> On Wednesday 06 July 2005 02:36 pm, Juergen Wieferink wrote:
>> But I have placed the "#ifdef" quite funny, did you notice?  
>
> I noticed. But then, we *had* been discussing whether to remove
> the conditional coding around string variables. I figured you
> were just off to a quick start :-) 
>

That reminds me...  there's a couple of memory/cleanup issues been
mentioned recently, and IIRC, there used to be a problem with
memory leaks if SIGINT is sent during a plot, since the exact state is
unknown, and so data structures cannot safely be traversed and freed.

I was wondering if there's a case for some sort of garbage
collection. Nothing sophisticated like moving memory around, updating
pointers, etc. Just simple reference counting (probably).
Perhaps something along the lines of:

allocated blocks are kept in linked lists : say a list of "permanent"
blocks (eg udf's), and a list of transient blocks (allocated during a
plot, for example). At end of a plot, everything in the transient list
is reclaimed.

items can have a reference count (eg for strings, rather than making a
copy, just increase the ref count on copy, and decrease it when the
string goes out of scope)

items can have cleanup routines.
 - eg for the recent issue with c++ destructors, the cleanup routine
 could be a c++ fn to cleanup objects
 - cleanup routine for an 'at' can in turn free string literals, etc.


Need to be a little careful with registration of non-trivial objects,
to make sure things are atomic wrt SIGINT. But I think it should be
do-able. All the allocation used to go through a common routine, so
it shouldn't be hard to intercept all allocs and frees.


dd
-- 
Dave Denholm              <dde...@es...>       http://www.esmertec.com