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Re: adding destroyable objects into Ggc

On Thu, 20 Oct 2011, Basile Starynkevitch wrote:

On Wed, 19 Oct 2011 21:17:47 -0700
Lawrence Crowl <> wrote:

Basile Starynkevitch <>
I would like to add destroyable objects into Ggc (the GCC garbage
collector, see files gcc/ggc*.[ch]).

The main motivation is to permit C++ objects to be garbage collected
(I discussed that briefly in the Gcc meeting at Google in London):
adding destroyable object is a prerequisite for that goal.

The C++ standard has support for garbage collection, and the general consensus of the committee is that object garbage collected do not execute their destructors.

I don't understand well this decision.

If you just let the objects leak, their destructor is not executed. Garbage collection reuses that memory in such a way that you can't notice the difference with a leak (except that you don't get OOM).

PPL [Parma Polyhedra Library] data, like e.g. ppl_Constraint_t [from header <ppl_c.h> that is, using a C API] comes to mind. If you want to share PPL stuff between several passes, it can be very handy to add PPL data inside GTY-ed stuff. If that GTY-ed stuff is deleted by Ggc, and if the PPL destructor (e.g. ppl_delete_Constraint in that case) is not called, you get a memory leak.

Or you could imagine the garbage collector also reclaiming that memory.

Other usages include other finalized data, like FILE* [if a plugin need a FILE* inside GTY-ed data to be shared by several passes, it would be handy that when the GTY-ed object is deleted, the FILE* is fclosed] or even std::ostringstream or std::ostring-s shared between several passes.

Yes, those are the usual arguments for a finalizer.

Marc Glisse

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