[Rd] Pointer ownership with GECreateDevDesc/GEDestroyDevDesc

[Ritch Melton]

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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