Pointer ownership with GECreateDevDesc/GEDestroyDevDesc

I perused the source for RStudio and noticed that they had a similar
problem. I didn't think that the GEDevDesc structure was exported, but
apparently this is a worthwhile workaround to the defect.

void GD_Close(pDevDesc dev)
{
...elided...
       // explicitly free and then null out the dev pointer of the GEDevDesc
       // This is to avoid incompatabilities between the heap we are
compiled with
       // and the heap R is compiled with (we observed this to a problem with
       // 64-bit R)
       std::free(s_pGEDevDesc->dev);
       s_pGEDevDesc->dev = NULL;

       // set GDDevDesc to NULL so we don't reference it again
       s_pGEDevDesc = NULL;
    }
}

I will

On Fri, Sep 19, 2014 at 10:37 AM, Ritch Melton <skyguy94 at gmail.com> wrote:

According to the "R Internals" document, for a custom device, I should
create a pDevDesc structure that gets passed to GECreateDevDesc.

..elided...
pDevDesc dev;
/* Allocate and initialize the device driver data */
if (!(dev = (pDevDesc) calloc(1, sizeof(DevDesc)))) return 0;
/* or error() */
/* set up device driver or free ?dev? and error() */
gdd = GEcreateDevDesc(dev); GEaddDevice2(gdd, "dev_name");
...elided...

which indicates to me that the calling code owns the pDevDesc structure
and should be responsible for freeing it.
However, in GEdestroyDevDesc, that particular code calls free(dd->dev),
freeing the pointer.

In my case, I have a device implemented and created in a language that is
using a different allocator. The pDevDesc I pass in is not owned by R and
causes a crash on free with "dev.off()".

I thought I could mitigate the issue, by making a call to the allocator R
is using via an exported R function, such as R_alloc, but I did not see
such a function available to me.

I would like to know if I should be creating the pDevDesc via an imported
alloc routine somehow? or is there a way to prevent this code from freeing
the structure I pass in.

Blue Skies,
Ritch

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