On 05/07/2009 10:54 AM, Yuri D'Elia wrote:
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.
The normal way to do what you want is to use an "external pointer". R
assumes that memory management for those is handled completely
externally. External pointers can have finalizers, so when you no
longer have a need for the object, you can ask the external library to
release it.
- create a normal LISTSXP in the package, which holds a reference
to all these objects, so that GC never takes place.
The list would hold the external pointers, which act like references.
- 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.
That won't happen.
I wouldn't try to trick the memory manager into thinking that it
allocated these things; that will likely just lead to problems.
Duncan Murdoch
Would that approach work?
Are there any alternative approaches?
Any specific advice about turning these objects read-only?
Thanks in advance.
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