[Rd] Request: Increasing MAX_NUM_DLLS in Rdynload.c

[Karl Millar]

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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