[Rcpp-devel] Raise a condition

[Tim Keitt]

On Wed, Jun 18, 2014 at 5:37 PM, Romain Francois <romain at r-enthusiasts.com>
wrote:

> Le 19 juin 2014 à 00:30, Tim Keitt <tkeitt at utexas.edu> a écrit :
>
> On Wed, Jun 18, 2014 at 5:22 PM, Romain Francois <romain at r-enthusiasts.com
> > wrote:
>
>> Le 19 juin 2014 à 00:15, Tim Keitt <tkeitt at utexas.edu> a écrit :
>>
>>
>>
>> On Wed, Jun 18, 2014 at 5:07 PM, Romain Francois <
>> romain at r-enthusiasts.com> wrote:
>>
>>> Le 18 juin 2014 à 23:54, Tim Keitt <tkeitt at utexas.edu> a écrit :
>>>
>>>
>>> I'd like to raise a condition other than error or warning. Is that
>>> possible using the Rcpp api? I assume this can be done via R internals, but
>>> I'd prefer not to call error() directly (or is that the recommendation?).
>>>
>>> THK
>>>
>>>
>>> Definitely not. Rf_error should really only be called from C code. If
>>> you call it from C++, there is a great chance you'll lose determinism as
>>> destructors for your c++ objects are very likely not to be called. Most of
>>> the time, it will just mean you'll never release some objects to the
>>> garbage collector, but it could also get you leaks or other nice stuff
>>> depending on what your destructors were supposed to do and did not get a
>>> chance to do.
>>>
>>
>> That was my understanding. Just wanted to be sure it was still the case.
>>
>>
>>>
>>> I'm not sure Rcpp has a way to raise an R condition apart from calling
>>> stop, which usually is good enough. Otherwise, you can borrow from Rcpp11
>>> and adapt some code from
>>> https://github.com/Rcpp11/Rcpp11/blob/450aade7338c16c34618ad0916003e8ca4fb58a6/inst/include/Rcpp/Condition.h
>>>
>>
>> Ah. I see. Eval "stop" in the global env with the condition as the
>> argument. Clever.
>>
>>
>> It is more of a hack due to lack of proper api from R.
>>
>> If you do this, make sure you don't have any c++ object in scope.
>> Essentially that means you would evaluate `stop( condition )` in a top
>> level catch block.
>>
>
> Rcpp objects are I assume ok however.
>
>
> Depends what you mean by "ok". If you mean objects like NumericVector, ...
> their destructor is responsible for calling R_ReleaseObject, i.e. let go of
> the protection that was set by their constructor. If the destructor is not
> called because R error handling does a long jump, you will get objects
> forever protected.
>
> So things will seemingly work, until you exhaust the memory.
>
> I will try "signalCondition" and see what happens.
>
> THK
>
>
>
I can't get signalCondition to do anything. This works although I've not
tested it for leaks.

void raise_condition(const std::string& msg,
                     const std::string& type)
{
  List cond;
  cond["message"] = msg;
  cond["call"] = R_NilValue;
  cond.attr("class") = CharacterVector::create(type, "condition");
  Function stopper("stop");
  stopper(cond);
}

THK

-- 
http://www.keittlab.org/
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