c - matrix multiplication using thread where each thread compute a row -


  1. hello guys , wrote below code matrix multiplication using thread, each thread should compute row when run code gives me correct result first row , other rows of elements zeros. martix size of m*m !! can't find mistake !!thanks in advance 

            # include <stdio.h>         # include <pthread.h>         # include <stdlib.h>         #include <sys/time.h>         int m;         int [100][100];          int b [100][100];         int c [100][100];          struct v {            int i; /* row */            int j; /* column */         };          void *runner(void *param); /* thread */ 
            int main()         {         clock_t cstart = clock();           clock_t cend = 0;            int count=0;            pthread_t tid;                 int icount,jcount,kcount;         printf("enter size: \n");         scanf("%d",&m);         for(icount=0;icount<m;icount++)             {                 for(jcount=0;jcount<m;jcount++)                 {                     printf("enter mat1[%d][%d] :",icount,jcount);                     scanf("%d",&a[icount][jcount]);                 }             }         for(icount=0;icount<m;icount++)             {                 for(jcount=0;jcount<m;jcount++)                 {                     printf("enter mat2[%d][%d] :",icount,jcount);                     scanf("%d",&b[icount][jcount]);                 }             }          for(icount = 0; icount < m; icount++) {                  struct v *data = (struct v *) malloc(sizeof(struct v));                  data->i = icount;                  data->j = jcount;                  pthread_t tid;                         pthread_attr_t attr;                   pthread_attr_init(&attr);                  pthread_create(&tid,&attr,runner,&c[icount]);                  pthread_join(tid, null);                  count++;            }           printf("\n matrix 1 \n");              for(icount=0;icount<m;icount++)             {                 for(jcount=0;jcount<m;jcount++)                 {                     printf("%d \t",a[icount][jcount]);                 }                 printf("\n");             }                  printf("\n matrix 2 \n");              for(icount=0;icount<m;icount++)             {                 for(jcount=0;jcount<m;jcount++)                 {                     printf("%d \t",b[icount][jcount]);                 }                 printf("\n");             }           printf("\n multipication of matrices ...\n");            for(icount = 0; icount < m; icount++) {               for(jcount = 0; jcount < m; jcount++) {                  printf("%d \t", c[icount][jcount]);               }               printf("\n");            }         cend = clock();           printf ("it took %.3f cpu sec\n", ((double)cend - (double)cstart)* 1.0e-6);         return 0;        } 
            void *runner(void *param) {            struct v *data = param;             int n, sum = 0;             int jcount;         do{sum=0;            for(n = 0; n< m; n++){               sum += a[data->i][n] * b[n][data->j];            }            c[data->i][data->j] = sum;          data->j++;         }while(data->j<m);            pthread_exit(0);         } 
       // compile code : gcc thread.c -o out -pthread   //                 ./out

the mistake here in thread creation loop:

data->j = jcount;

you should initialize data->j 0. instead initialize jcount value m @ end of matrix initialization phase. data->j not make sense thread argument each thread computes whole column.


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