# Example for aio_read and aio_write Functions

The example illustrates the performance gain of the asynchronous I/O usage in comparison with synchronous I/O usage. In the example, 5.6 MB of data is asynchronously written with the main program computation, which is the scalar multiplication of two vectors with some normalization.

С-source file executing a scalar multiplication:

    #include <math.h>
    #include <stdio.h>
    #include <stdlib.h>

    double do_compute(double A, double B, int arr_len)
    {
      int i;
      double   res = 0;
      double  *xA = malloc(arr_len * sizeof(double));
      double  *xB = malloc(arr_len * sizeof(double));
      if ( !xA || !xB )
       abort();
       for (i = 0; i < arr_len; i++) {
        xA[i] = sin(A);
        xB[i] = cos(B);
        res = res + xA[i]*xA[i];
       }
      free(xA);
      free(xB);
     return res;
    }

C-main-source file using asynchronous I/O implementation:

    #define DIM_X   123/*123*/
    #define DIM_Y   70000
    double  aio_dat[DIM_Y /*12MB*/] = {0};
    double  aio_dat_tmp[DIM_Y /*12MB*/];

    #include <stdio.h>
    #include <aio.h>

    typedef struct aiocb  aiocb_t;
       aiocb_t   my_aio;
       aiocb_t  *my_aio_list[1] = {&my_aio};

    int main()
    {
      double do_compute(double A, double B, int arr_len);
      int i, j;
      HANDLE fd = CreateFile("aio.dat",
      GENERIC_READ | GENERIC_WRITE,
      FILE_SHARE_READ,
      NULL,
      OPEN_ALWAYS,
      FILE_ATTRIBUTE_NORMAL,
      NULL);
    /* Do some complex computation */
    for (i = 0; i < DIM_X; i++) {
     for ( j = 0; j < DIM_Y; j++ )
     aio_dat[j] = do_compute(i, j, DIM_X);

      if (i) aio_suspend(my_aio_list, 1, 0);
      my_aio.aio_fildes = fd;
      my_aio.aio_buf    = memcpy(aio_dat_tmp, aio_dat, sizeof(aio_dat_tmp));
      my_aio.aio_nbytes = sizeof(aio_dat_tmp);
      my_aio.aio_offset = (intptr_t)-1;
      my_aio.aio_sigevent.sigev_notify = SIGEV_NONE;

      if ( aio_write((void*)&my_aio) == -1 ) {
      printf("ERROR!!! %s\n", "aio_write()==-1");
      abort();}
      }
     aio_suspend(my_aio_list, 1, 0);
     return 0;
    }

C-main-source file example 2 using asynchronous I/O implementation:

    // icl -c do_compute.c
    // icl aio_sample2.c do_compute.obj
    // aio_sample2.exe

    #define DIM_X   123
    #define DIM_Y    70
    double  aio_dat[DIM_Y] = {0};
    double  aio_dat_tmp[DIM_Y];
    static volatile int aio_flg = 1;

    #include <aio.h>
    typedef struct aiocb  aiocb_t;
    aiocb_t               my_aio;
    #define WAIT { while (!aio_flg); aio_flg = 0; }
    #define aio_OPEN(_fname )\
    CreateFile(_fname,                       \
               GENERIC_READ | GENERIC_WRITE, \
               FILE_SHARE_READ,              \
               NULL,                         \
               OPEN_ALWAYS,                  \
               FILE_ATTRIBUTE_NORMAL,        \
               NULL)

    static void aio_CompletionRoutine(sigval_t sigval)
    {
        aio_flg = 1;
    }

    int main()
    {
        double do_compute(double A, double B, int arr_len);
        int      i, j, res;
        char    *fname = "aio_sample2.dat";
        HANDLE   aio_fildes = aio_OPEN(fname);

        my_aio.aio_fildes = aio_fildes;
        my_aio.aio_nbytes = sizeof(aio_dat_tmp);
        my_aio.aio_sigevent.sigev_notify          = SIGEV_THREAD;
        my_aio.aio_sigevent.sigev_notify_function = aio_CompletionRoutine;

        /*
        ** writing
        */
        my_aio.aio_offset = -1;
        printf("Writing\n");
        for (i = 0; i < DIM_X; i++) {
            for (j = 0; j < DIM_Y; j++)
                aio_dat[j] = do_compute(i, j, DIM_X);
            WAIT;
            my_aio.aio_buf = memcpy(aio_dat_tmp, aio_dat, sizeof(aio_dat_tmp));
            res = aio_write(&my_aio);
            if (res) {printf("res!=0\n");abort();}
        }

        //
        // flushing
        //
        printf("Flushing\n");
        WAIT;
        res = aio_fsync(O_SYNC, &my_aio);
        if (res) {printf("res!=0\n");abort();}
        WAIT;

        //
        // reading
        //
        printf("Reading\n");
        my_aio.aio_offset = 0;
        my_aio.aio_buf    = (volatile char*)aio_dat_tmp;
        for (i = 0; i < DIM_X; i++) {
            aio_read(&my_aio);
            for (j = 0; j < DIM_Y; j++)
                aio_dat[j] = do_compute(i, j, DIM_X);
            WAIT;
            res = aio_return(&my_aio);
            if (res != sizeof(aio_dat)) {
                printf("aio_read() did read %d bytes, expecting %d bytes\n", res, sizeof(aio_dat));
            }

            for (j = 0; j < DIM_Y; j++)
                if ( aio_dat[j] != aio_dat_tmp[j] )
                    {printf("ERROR: aio_dat[j] != aio_dat_tmp[j]\n I=%d J=%d\n", i, j); abort();}
            my_aio.aio_offset += my_aio.aio_nbytes;
        }

        CloseHandle(aio_fildes);

        printf("\nDone\n");

    return 0;
    }

Parent topic: Intel's C++ Asynchronous I/O Library for Windows

## See Also

aio_read()
aio_write()