Re: [Rd] C/C++ 'assert' should not be used in R packages

From: Henrik Bengtsson <hb_at_stat.berkeley.edu>
Date: Fri, 16 Nov 2007 15:58:47 -0800

On Nov 10, 2007 1:27 PM, Simon Urbanek <simon.urbanek_at_r-project.org> wrote:
>
>
> On Nov 10, 2007, at 1:05 PM, Duncan Murdoch wrote:
>
> > On 10/11/2007 1:00 PM, Duncan Temple Lang wrote:
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> >>
> >>
> >> Duncan Murdoch wrote:
> >>> Prof Brian Ripley wrote:
> >>>> Please don't use 'assert' in R packages. If called, this means
> >>>> that an
> >>>> error in your code aborts the whole R process, including your
> >>>> user's work.
> >>>> I see several R packages doing this, and one of them called
> >>>> 'assert' on me
> >>>> earlier in the week.
> >>>>
> >>> I partly disagree about this. If assert() is triggered, it clearly
> >>> indicates a bug in the package. If it just generated an R error,
> >>> most
> >>> users would ignore it, and not report it to the package maintainer.
> >>>
> >>> It may well be that when an assertion fails, none of the subsequent
> >>> calculations are reliable, in which case returning control to the
> >>> user
> >>> could result in data corruption. That's worse than losing a
> >>> session,
> >>> because at least when you lose a session, you know it.
> >>>
> >>> Could we write our own implementation of assert() that displays an R
> >>> error and unloads the package? I think I could do something like
> >>> that
> >>> in Windows by calling FreeLibrary to unload the DLL, but I'd
> >>> prefer a
> >>> cross-platform solution.
> >>
> >> I am not sure why you think we need to discard the DLL.
> >
> > The package author has asserted that it is no longer safe to run.
> > They are shutting down R, and Brian finds that too extreme.
> >
>
> Me too. A package should never intentionally close the R session. If
> it does, it is a very severe design bug in the package (IMHO).
> Anything you use assert for can be gracefully handled (as opposed to
> let's say a segfault), so there is no excuse for killing the whole
> process at all (deliberately wiping all user's work is rude to put it
> mildly).

Oh, I normally try to wipe the harddrive too when I'm at it ;)

/H

> Even if it might be unsafe to run anything, I'd still want
> to attempt to save my data.
>
> Cheers,
> Simon
>
>
>
> >> What if we want to access variables and routines merely to find out
> >> the resulting state after the assert().
> >> And it is not clear whether you mean any "subsequent calculations"
> >> or any "subsequent calculations using code within this DLL"
> >> might be unreliable.
> >
> > How could I know why a package author decided a shutdown is
> > needed? It
> > depends on the author.
> >
> >>
> >> But regardless of that and the assumption that users will ignore this
> >> error, why would you want to call FreeLibrary? Since R has induced
> >> the
> >> DLL to be loaded either directly or indirectly, R holds a handle
> >> to the
> >> DLL. If you don't use R's cross-platform facilities for releasing the
> >> DLL (either at the R or C-level), you will corrupt the session,
> >> specifically in the list of assumed-live DLLs.
> >
> > As I said, I'd prefer a cross-platform solution.
> >
> > Duncan Murdoch
> >>
> >> D.
> >>
> >>
> >>>> We provide 'error': please do use it to return control to the
> >>>> user when
> >>>> your code misbehaves.
> >>>>
> >>>> Similarly 'exit' and 'abort' should never be used in R packages.
> >>>>
> >>>>
> >>>> Sometimes it is not under your control: I sometimes see an rgl
> >>>> failure at
> >>>>
> >>>> R: indirect_vertex_array.c:659: emit_DrawArrays_old: Assertion
> >>>> `elements_per_request >= count' failed.
> >>>>
> >>>> that is coming from the Mesa GL libraries.
> >>>>
> >>> I'd say that's a bug, either in Mesa GL or in rgl. If you can
> >>> make it
> >>> reproducible, I'll try to track it down.
> >>>
> >>> Duncan Murdoch
> >>>
> >>> ______________________________________________
> >>> R-devel_at_r-project.org mailing list
> >>> https://stat.ethz.ch/mailman/listinfo/r-devel
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> >
> >
>
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