shared mem advice
On Tue, 13 Apr 2004, Alex Nu wrote:
Hi, I want to write a package where I would use shared memory for some vectors Any suggestion is appreciated...
I'd recommend looking at external pointer objects. If the developer webpage were working, that would be the place to look. I'm not sure where else there is information.
I wonder if the right approach would be to
modify add a modified version of the
allocVector(SEXPTYPE type, int length) function
specifically
shared_mem_id = shmget(shared_mem_key,
SHM_SIZE,
IPC_CREAT);
shared = (SEXP) shmat(shared_mem_id, (void *)0, 0);
No, you want the shared memory to hold the data of the vector, not the header record that the SEXP points to. If you do it this way you want to look at how memory.c:allocVector uses malloc() for large vectors. -thomas
my_allocVector(SEXPTYPE type, int length, SEXP
shared) {
SEXP s=shared;
....
And erase this if:
#################################################
if(size >=
(LONG_MAX / sizeof(VECREC))-sizeof(SEXPREC_ALIGN)
||
(s =
malloc(sizeof(SEXPREC_ALIGN) + size *
sizeof(VECREC))
)
== NULL) { {
#################################################
Alex
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Thomas Lumley Assoc. Professor, Biostatistics tlumley@u.washington.edu University of Washington, Seattle