[Rd] Request: Increasing MAX_NUM_DLLS in Rdynload.c

Henrik Bengtsson henrik.bengtsson at gmail.com
Wed Dec 21 18:10:33 CET 2016

On Tue, Dec 20, 2016 at 7:39 AM, Karl Millar <kmillar at google.com> wrote:
> It's not always clear when it's safe to remove the DLL.
> The main problem that I'm aware of is that native objects with
> finalizers might still exist (created by R_RegisterCFinalizer etc).
> Even if there are no live references to such objects (which would be
> hard to verify), it still wouldn't be safe to unload the DLL until a
> full garbage collection has been done.
> If the DLL is unloaded, then the function pointer that was registered
> now becomes a pointer into the memory where the DLL was, leading to an
> almost certain crash when such objects get garbage collected.

Very good point.

Does base::gc() perform such a *full* garbage collection and thereby
trigger all remaining finalizers to be called?  In other words, do you
think an explicit call to base::gc() prior to cleaning out left-over
DLLs (e.g. R.utils::gcDLLs()) would be sufficient?


> A better approach would be to just remove the limit on the number of
> DLLs, dynamically expanding the array if/when needed.
> On Tue, Dec 20, 2016 at 3:40 AM, Jeroen Ooms <jeroen.ooms at stat.ucla.edu> wrote:
>> On Tue, Dec 20, 2016 at 7:04 AM, Henrik Bengtsson
>> <henrik.bengtsson at gmail.com> wrote:
>>> On reason for hitting the MAX_NUM_DLLS (= 100) limit is because some
>>> packages don't unload their DLLs when they being unloaded themselves.
>> I am surprised by this. Why does R not do this automatically? What is
>> the case for keeping the DLL loaded after the package has been
>> unloaded? What happens if you reload another version of the same
>> package from a different library after unloading?
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