Re: [Chicken-users] GC root gets garbage collected

[Christopher Collins]

Thanks, Peter.

The C code always uses CHICKEN_gc_root_ref() to obtain the reference
that it passes to the scheme code.

Also, something that I didn't make very clear: after creating the root
as paraphrased in my previous email, the C code successfully passes
the struct reference to a scheme procedure several hundred times.
But, eventually, immediately after the garbage collector runs, the
next call to the scheme function fails.  I can see the relative timing
of the garbage collector via a call to (set-gc-report! #t).

I am not enabling symbol garbage collection, so I don't think that bug
you referenced is the problem.

Anyway, I just mention the above as clarification.  I will do some
more investigation and work on coming up with a self-contained
example.  Thanks a lot for the quick response.

Chris

On Thu, Mar 19, 2015 at 12:45 PM, Peter Bex <address@hidden> wrote:
> On Thu, Mar 19, 2015 at 12:21:47PM -0700, Christopher Collins wrote:
>> The way I understood it, the returned "mystruct" instance would never get
>> garbage collected until I explicitly call CHICKEN_delete_gc_root().  I never
>> actually delete the root (I set a breakpoint on CHICKEN_delete_gc_root in 
>> gdb,
>> just to be sure), but the object gets garbage collected anyway.  The next 
>> time
>> I try to pass the instance of mystruct to a scheme procedure, the procedure
>> fails because the argument is not of the expected type (when I print the
>> argument, I see " #<invalid forwarded object>").
>
> Hello Christopher,
>
> How are you accessing the object?  If it's from C, you need to use GC_root_ref
> to obtain a fresh reference to the object; you can't use a stale reference
> to the object you saved in the GC root.
>
>> I must be confused about how gc roots work.  Am I doing anything that is
>> obviously wrong?  I can try to post some real code if that would help.
>
> It would certainly help if you posted a minimal example of the failing
> situation.  I don't immediately saw anything wrong with the bit you
> posted, but it only showed how you saved the object, not how the rest
> of the code uses it.
>
> Also, please be aware of http://bugs.call-cc.org/ticket/1173; you'll only
> run into that if you enable symbol GC though, which happens when you
> pass -:w to a CHICKEN program or set C_enable_gcweak to nonzero.
>
> Cheers,
> Peter