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shared mem advice

3 messages · Alex Nu, Thomas Lumley, Peter Dalgaard

Alex Nu
# 
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
Thomas Lumley
#
On Tue, 13 Apr 2004, Alex Nu wrote:

            

      
      
      
    

        
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.

            

      
      
      
    

        
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

            

      
      
      
    

        

      
      
    

        
Thomas Lumley			Assoc. Professor, Biostatistics
tlumley@u.washington.edu	University of Washington, Seattle

  
  


  


      

    

    

      
      

        


  

        

      Peter Dalgaard
    

    

      
      #
    

  


  

      
Thomas Lumley <tlumley@u.washington.edu> writes:

            

      
      
      
    

        
http://www.stat.uiowa.edu/~luke/R is a good guess. Apart from that,
there's some relatively simple usage of such things in the tcltk
package.