Some head scratching this morning.
If I have this:
return Rcpp::List::create(Rcpp::Named( "testVar" ) = 10 ) ;
instead of:
return Rcpp::List::create(Rcpp::Named( "testVar" ) = wrap(10) ) ;
everything runs smoothly.
So my guess is that the SEXP that is made in the wrap call does not get
sufficient protection.
Not sure this is an Rcpp bug or a user bug, but there might be somethign
I can do to prevent it.
Romain
Le 31/03/12 09:20, Ilya E a ?crit :
(Apologies for sending this twice -- the formatting on the first email
got completely mangled)
Are there any known issues regarding memory corruption caused by lists
created inside of Rcpp? I started noticing some inconsistencies in the
data returned by my app, and was able to reduce the issue to the
following reproducible example. It seems to suggest that lists created
in Rcpp and returned to R can cause sporadic memory corruption. See
code below for a demonstration:
require(inline)
require(Rcpp)
testFun <- local( {
fun <- cxxfunction(
signature(), '
return Rcpp::List::create(Rcpp::Named( "testVar" ) = wrap(10));
', plugin = "Rcpp" )
function(){
fun()
}
} )
# generate the result set -- you would expect a numeric vector that
consists of repetition of the value 10
testOutcome = mapply(
function(i) {
fTouch = testFun()
return(fTouch$testVar)
},
1:5612062)
# The result ensd up being something other than what you'd expect
typeof(testOutcome)
for (i in 1:length(testOutcome)) {
if (testOutcome[[i]] != 10) {
cat(i, "\n")
}
}
You'll notice two things here. First, mapply fails to coerce the
returned results to a vector (since in some cases the return from
testFun seems to have more than 1 element) and second, not all return
values are equal to 10, as you would expect. The actual position in
the vector of the corrupted data is sporadic. If you keep running this
over and over again, you'll see the wrong value in different places.
Sometimes you can even get R to crash after multiple runs. On rare
occasions there will be no errors at all. For some reason you tend to
see the most errors on the first run, especially if you open a new
instance of R.
If you replace the line "fTouch = testFun()" with a native call to R
"fTouch = list(testVar = 10)" then everything works fine. Also
returning a NumericVector instead of a list also works fine -- the
issue seems to appear after encapsulating the return value in a list
inside of Rcpp.
I am using R 2.14.2 on Win32& Win64. Rcpp version 0.9.10.
Thanks,
Ilya