使用pthread并行编程

Question

I have just started learning parallel programming using pthreads . So, for the learning purpose I tried sum of two integer arrays parallely. I have declared struct construct with three array variables a , b and c . I want to do addition of a , b and store the result in c .

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

#define MAX 6

struct data {
  int a[MAX];
  int b[MAX];
  int c[MAX];
};

void *addition(void *index) {
  struct data *d1 = (struct data *)index;
  printf("value of d1 structure=%d\n", d1->a[0]);
}

int main() {
  int i, j, t;
  struct data *item = NULL;
  pthread_t threads[MAX];

  item = (struct data *)malloc(sizeof *item);

  printf("enter the value for arrray a\n");
  for (i = 0; i < MAX; i++) {
    scanf("%d", &item->a[i]);
  }

  printf("enter the value of array b\n");
  for (j = 0; j < MAX; j++) {
    scanf("%d", &item->b[j]);
  }

  for (t = 0; t < MAX; t++) {
    pthread_create(&threads[t], NULL, addition, (void *)&item);
  }
}

Here, as of now I have not added the addition of arrays in the function addition() , because in pthread_create() when I am passing the three arguments with the help of structure , in function addition the variables a and b are not getting copied. Printing a is giving me garbage value. Can anybody help me how to copy the structure variable to the function argument called by pthread_create() .

Answer 1

pthread_create Function :

int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
                          void *(*start_routine) (void *), void *arg);

Kindly note (*arg) is pointer to the arg . You have created struct data *item as a pointer then you are passing its address ie pointer to pointer.

pthread_create(&threads[t], NULL, addition, (void *)&item);

Change the call to

pthread_create(&threads[t], NULL, addition, (void *)item).