Problem with "in" clause

[Hamidreza_K_]

Hi all,

I wrote a simple application, attached at following, using offloads and streams and made a local copy from variable i for each stream with clause in. After the program was executed, I found that variable i is shared among all streams. Please let me know how we can create a local copy for a variable in offloads that other offloads cannot change its value.

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#include"stdio.h"
#include"offload.h"
#include <mkl.h>
#include <miclib.h>

#include <unistd.h>

#define    ALLOC        alloc_if(1)
#define FREE        free_if(1)
#define RETAIN    free_if(0)
#define REUSE   alloc_if(0)

const int SIZE=4;

int i,j,m,n,k;

main()
{
    _Offload_stream handle[SIZE];
    
    for(i=0; i< SIZE; i++)
        handle = _Offload_stream_create(0, 1);
    
    m=n=k= 3000;
    
    double *a,*b,*c;
    
    a = (double *)malloc(m*k*sizeof(double));
    b = (double *)malloc(n*k*sizeof(double));
    c = (double *)malloc(m*n*sizeof(double));
    
    for(i = 0; i<m*n; i++)
        a = b = c = i;
  
    #pragma offload_transfer target (mic) in(a:length(m*k) ALLOC RETAIN) 
    #pragma offload_transfer target (mic) in(b:length(k*n) ALLOC RETAIN) 
    #pragma offload_transfer target (mic) in(c:length(m*n) ALLOC RETAIN) 
    #pragma offload_transfer target (mic) in(m,n,k: ALLOC RETAIN)
    
    for(i=0;i<SIZE;i++)
    {
        //#pragma offload_transfer target (mic) in(i: ALLOC RETAIN) stream(handle)
        
        #pragma offload target (mic) in(i: ALLOC FREE) nocopy(a,b,c, m,n,k: REUSE RETAIN) stream(handle)
        {
            fprintf(stderr, "start, i = %i\n", i);
            char trans = 'N';
            double alpha, beta;
            alpha = beta = 1;
            dgemm(&trans, &trans, &m, &n, &k, &alpha, a, &m, b, &m, &beta, c, &m);
            fprintf(stderr, "stop, i = %i\n", i);
        }
        
        usleep( 1000 * 1000 );
    }
    
    i = 1000;
    #pragma offload_wait target(mic) stream(0)
}

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output is:

start, i = 0
start, i = 1
start, i = 2
start, i = 3
stop, i = 3
stop, i = 3
stop, i = 3
stop, i = 3

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[Hamidreza_K_]

I found that variable i should be defined in main block. Could somebody explain why defining variable i globally resulted in the aforementioned problem?

[Kevin_D_Intel]

It is inherent in the design of the offload language extensions. File scope variable's (i.e. static data) values are always maintained and persist across offloads. Function scope variable's (i.e. stack data) values are not persistent across offloads.

The function scope variable is best suited for what you describe wanting.

Also, just FYI, alloc_if/free_if modifiers only apply to pointer data. The uses with variable ‘i’ are not applicable in your example.

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