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Duncan Murdoch wrote: > On 10/11/2007 1:00 PM, Duncan Temple Lang wrote: > > > 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. I don't think this is worth spending much time on other than to encourage you not to use FreeLibrary or its equivalents on other systems and to use the R mechanisms. However, just to clarify. > >> The package author has asserted that it is no longer safe to run. run _what_ ? The R session? The computer? .... The object is important here. assert() typically means that something unexpected in that routine or in our case the sequence of calls from .C/.Call/... So to assume that the session is no longer safe seems to be a large leap from this particular invocation is unsafe to run to normal completion. As with most things, it is a matter of scope and a simple mechanism such as assert() leaves the intentions of the programmer unclear. But of course it should not terminate the R session. Nor should R package developers link to libraries that make call the C routine exit() as this too will terminate the R session. One can use techniques to mask such calls to exit() in some circumstances. >> They >> are shutting down R, and Brian finds that too extreme. > > 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@r-project.org mailing list >>>> https://stat.ethz.ch/mailman/listinfo/r-devel -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHNgoJ9p/Jzwa2QP4RAkeQAJ0Y0sMwWmb0k0u+3YI2lPXwBklpFQCfbCbk sY72JmcqQ78DQClVxIJKoKU= =3ZzG -----END PGP SIGNATURE----- ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
