On 24/11/2015 6:20 PM, Andrew Piskorski wrote:
On Tue, Nov 24, 2015 at 12:10:12AM +0100, Jeroen Ooms wrote:
Currently it is all to easy for package authors to introduce a memory
leak or stack imbalance by calling Rf_error() or
R_CheckUserInterrupt() in a way that skips over the usual cleanup
steps.
I have a more modest request: Please improve the documentation of
exactly what Rf_error() does and how it should be used! E.g., does
calling it terminate execution of the C function from which it is
called, or not? The docs below don't actually say:
https://cran.r-project.org/doc/manuals/r-devel/R-exts.html#Error-handling
https://cran.r-project.org/doc/manuals/r-devel/R-ints.html#Warnings-and-errors
The docs imply that these are "C-level equivalents" to the R stop()
function, which of course DOES terminate execution. I believe
Rf_error() does also, but I really wish it was explicitly stated one
way or the other.
I'd imagine the author of that section thought it *was* explicit. The
documentation can't answer every question, or clarify every
misunderstanding. That's why R-devel exists. fortune("source")
is also relevant. But now that you know the truth, you could suggest
rewording, as an svn patch against the trunk version of R-exts.texi.
Grepping the R source, I never did find where Rf_error() is actually
implemented. What am I missing?
You probably forgot to grep the .h files:
include\R_ext\Error.h(48): #define error Rf_error
The implementation of the function calls it error(), and uses the define
to remap that to Rf_error(). You can find the implementation in (where
else?) src/main/errors.c.
In src/include/Rinternals.h, the implementation of error_return()
first calls Rf_error(msg) and then does a separate "return R_NilValue"
in the next statement. So you might think that Rf_error() must NOT
terminate execution, otherwise why the extra return statement? But it
also has a comment:
/* return(.) NOT reached : for -Wall */
Meaning that that return statement is just to silence compiler
warnings, and is not supposed to be reached because Rf_error()
terminates execution. But this is a ridiculously roundabout way to
infer what the behavior of Rf_error() is supposed to be...
I won't disagree that you took a roundabout route to the right conclusion.
Duncan Murdoch
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