"Henrik Bengtsson" <[EMAIL PROTECTED]> writes:
> Hi,
>
> I'm troubleshooting some native code on Windows that very occationally
> (and semi-randomly) crashes R. Already looked at "everything", I just
> want to double check that it is safe to UNPROTECT() allocated
> variables as soon as they are assigned to, say, a PROTECTed list.
>
> >From (R v2.3.0) Section 5.7.1 "Handling the effects of garbage
> collection" in "Writing R Extensions":
>
> "In some cases it is necessary to keep better track of whether
> protection is really needed. Be particularly aware of situations where
> a large number of objects are generated. The pointer protection stack
> has a fixed size (default 10,000) and can become full. It is not a
> good idea then to just PROTECT everything in sight and UNPROTECT
> several thousand objects at the end. It will almost invariably
> possible to either assign the objects as part of another object (which
> automatically protects them) or unprotect them immediately after use."
>
> BTW, should it say "...another [protected] object..."?
Yes. (And the text could need general rephrasing too. I'm afraid that
I'm the guilty party.)
> Example from "5.7.4 Attributes" illustrating my question:
>
> SEXP out(SEXP x, SEXP y)
> {
> R_len_t i, j, nx, ny;
> double tmp;
> SEXP ans, dim, dimnames;
>
> nx = length(x); ny = length(y);
> PROTECT(ans = allocVector(REALSXP, nx*ny));
> for(i = 0; i < nx; i++) {
> tmp = REAL(x)[i];
> for(j = 0; j < ny; j++)
> REAL(ans)[i + nx*j] = tmp * REAL(y)[j];
> }
>
> PROTECT(dim = allocVector(INTSXP, 2));
> INTEGER(dim)[0] = nx; INTEGER(dim)[1] = ny;
> setAttrib(ans, R_DimSymbol, dim);
>
> *** It is safe to do UNPROTECT(1) for 'dim' already here, correct? ***
Yes. The protection of "ans" will carry over to its attributes.
> PROTECT(dimnames = allocVector(VECSXP, 2));
> SET_VECTOR_ELT(dimnames, 0, getAttrib(x, R_NamesSymbol));
> SET_VECTOR_ELT(dimnames, 1, getAttrib(y, R_NamesSymbol));
> setAttrib(ans, R_DimNamesSymbol, dimnames);
>
> UNPROTECT(3);
> return(ans);
> }
>
> Thanks
>
> /Henrik
>
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> https://stat.ethz.ch/mailman/listinfo/r-devel
>
--
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c/ /'_ --- Dept. of Biostatistics PO Box 2099, 1014 Cph. K
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