[Rd] Memory management issues

[Yuri D'Elia]

Hi everybody,

I have been interfacing some C++ library code into an R package but
ran into optimization issues specific to memory management that require
some insight into the GC.

One of the C++ libraries returns simple vectors of integers, doubles and
complex which are allocated and managed from the library itself. I
cannot know the length of the array beforehand, so I cannot
pre-allocate that memory through the GC.

Right now I'm allocating via allocVector and copying all the data in it.
However, this requires twice the amount of space (and time), and we're
running out of memory when doing concurrent analysis.

What I'd would like to do is:

- "patch" the SEXP returned to R so that DATAPTR() points directly to
  the required address. 

- create a normal LISTSXP in the package, which holds a reference
  to all these objects, so that GC never takes place.

- turn these objects read-only, or, at least, ensure that they are
  never free()d or remalloc()ed. overwriting the contents is not a
  critical issue.

Would that approach work?
Are there any alternative approaches?
Any specific advice about turning these objects read-only?

Thanks in advance.