[Rd] [External] Possible ALTREP bug

[iuke-tier@ey m@iii@g oii uiow@@edu]

integer and real Elt methods are not expected to allocate. You would
have to suspend GC to be able to do that. This currently can't be done
from package code.

Best,

luke

On Fri, 28 May 2021, Gábor Csárdi wrote:

> I have found some weird SEXP corruption behavior with ALTREP, which
> could be a bug. (Or I could be doing something wrong.)
>
> I have an integer ALTREP vector that calls back to R from the Elt
> method. When this vector is indexed in a lapply(), its first element
> gets corrupted. Sometimes it's just a type change to logical, but
> sometimes the corruption causes a crash.
>
> I saw this on macOS from R 3.5.3 to 4.2.0. I created a small package
> that demonstrates this: https://github.com/gaborcsardi/redfish
>
> The R callback in this package calls `loadNamespace("Matrix")`, but
> the same crash happens for other packages as well, and sometimes it
> also happens if I don't load any packages at all. (But that example
> was much more complicated, so I went with the package loading.)
>
> It is somewhat random, and sometimes turning off the JIT avoids the
> crash, but not always.
>
> Hopefully I am just doing something wrong in the ALTREP code (see
> https://github.com/gaborcsardi/redfish/blob/main/src/test.c), and it
> is not actually a bug.
>
> Thanks,
> Gabor
>
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-- 
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
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