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Re: New GCC plugin: gcc-python-plugin

On Wed, 2011-06-22 at 08:19 +0200, Jakub Jelinek wrote:
> Hi!
> On Tue, Jun 21, 2011 at 07:52:27PM -0400, David Malcolm wrote:
> > I'm not yet familiar with the details of the gcc GC, but it appears that
> > GTY() annotations are preprocessed to generate traversal code used by a
> > mark-and-sweep algorithm.
> > 
> > Python's own GC allows for classes to opt-in as reference-owners;
> > instances of such classes get tracked within linked lists (one per
> > generation of Python's GC).  This is intended for use for tracking
> > PyObject* references, but I may be able to piggy-back off of this - if I
> > add the relevant flag to my wrapper classes then they get tracked in
> > these linked lists.  I can then register a callback to
> > PLUGIN_GGC_MARKING that uses this to locate the subset of all PyObject*
> > objects that wrap GCC objects.  This could then mark all of the wrapped
> > GCC objects referenced from Python.  That way all of the Python wrapper
> > objects can be found as roots within a GCC GC, and thus not have their
> > wrapped GCC objects deleted "from under them" (traversing any refs they
> > in turn keep alive, of course).
> You could just:
> #include "ggc.h"
> static void my_walker (void *arg ATTRIBUTE_UNUSED)
> {
>   /* Ignore argument, as it is dummy */
>   /* Walk all the still live python objects here and if they reference
>      GCC GC objects, call
>   ggc_test_and_set_mark (ptr);
>      on each of them.  */
> }
> static struct ggc_root_tab myroot = { "", 1, 1, my_walker, NULL };
> ...
> init_plugin (...)
> {
> ...
>   ggc_register_root_tab (&myroot);
> ...
> }
> No need for gengtype for this, unless you want to use GTY(()) markup
> inside of your plugin.

[replying to 6-month old thread about integrating the Python plugin with
GCC's garbage collector]

Thanks.  FWIW, I implemented something like this in;a=commitdiff;h=58d65a1b353220efbcf8d908b0946ef5d1c4fafd

which iterates over all live wrapper objects calling
gt_ggc_mx_NAME_OF_TYPE() on each wrapped object, which I hope is the
correct approach [it seems to work: the selftest puts the machinery into
verbose mode, and then verifies this log:;a=blob;f=tests/plugin/gc/_gc_selftest/stdout.txt;hb=HEAD ]

Hope this is helpful

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