[Rd] Request: Increasing MAX_NUM_DLLS in Rdynload.c

Karl Millar kmillar at google.com
Tue Dec 20 16:39:32 CET 2016

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.

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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