[Rd] isoreg memory leak?

[Simon Urbanek]

On Jan 16, 2011, at 10:41 PM, Simon Wotherspoon wrote:

> 
> I believe there is a memory leak in isoreg in the current version of R, as I believe the following shows
> 
> > gc()
>         used (Mb) gc trigger (Mb) max used (Mb)
> Ncells 120405  3.3     350000  9.4   350000  9.4
> Vcells  78639  0.6     786432  6.0   392463  3.0
> > for(k in 1:100) {
> +
> +   y <- runif(10000)
> +   isoreg(x,y)
> + }
> > rm(x)
> > rm(y)
> > gc()
>         used (Mb) gc trigger (Mb) max used (Mb)
> Ncells 121637  3.3     350000  9.4   350000  9.4
> Vcells 578615  4.5    1300721 10.0  1300642 10.0
>               ^^^
> 
> 
> Looking at the C code, I believe the problem arises as a consequence of using SETLENGTH to resize the result near the very end of isoreg.c,
> and the solution is to make a copy of iKnots.
> 

AFAICS this is more of a reporting issue than a memory leak - ReleaseLargeFreeVectors() uses LENGTH() to determine the number by which to reduce R_LargeVallocSize - and it will be smaller than the actually released memory if SETLENGTH was used. I'm not sure how to fix it, because AFAICS the real size is not recorded anywhere (unless we use truelength for that but I'm not sure I know the implications). The good news is that it's not really a memory leak - the bad news is that the memory usage stats are rather an upper bound of the reality ;).

Cheers,
Simon



> 
> SEXP R_isoreg(SEXP y)
> {
>    int n = LENGTH(y), i, ip, known, n_ip;
>    double tmp, slope;
>    SEXP yc, yf, iKnots, ans;
>    const char *anms[] = {"y", "yc", "yf", "iKnots", ""};
> 
>    /* unneeded: y = coerceVector(y, REALSXP); */
> 
>    PROTECT(ans = mkNamed(VECSXP, anms));
> 
>    SET_VECTOR_ELT(ans, 0, y = y);
>    SET_VECTOR_ELT(ans, 1, yc = allocVector(REALSXP, n+1));
>    SET_VECTOR_ELT(ans, 2, yf = allocVector(REALSXP, n));
>    SET_VECTOR_ELT(ans, 3, iKnots= allocVector(INTSXP, n));
> 
> ... calculation ...
> 
>    SETLENGTH(iKnots, n_ip);
>    UNPROTECT(1);
>    return(ans);
> }
> 
> 
> But if this is the problem, I am at a bit of a loss as to what SETLENGTH is actually for in general.
> 
> Clearly my understanding of how allocation/gc works is a bit off here, but I can't see how else the leak may occur.  Hope this is more use than nuisance.
> 
> Simon.
> 
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