R devel - Apr 2004 - shared mem advice

Hi,

 I want to write a package where I would use
 shared memory for some vectors
 
 Any suggestion is appreciated...

 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);


 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

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