PThread Malloc上的分段错误

Question

First let me start by posting the code:

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

//64 BITS -ALL 32 bit Arch
//32 BIT - UNIX 64 bit arch
//64 BIT - WINDOWS 64 bit arch
long long sum = 0;
static enum turn
{
  PING,
  PONG
}def;

struct threads_util
{
  pthread_t *t_id;
  pthread_attr_t *attr;
  void (*init_attr)(pthread_attr_t *);
}; 

void init_attr_fn(pthread_attr_t *attr)
{
  pthread_attr_init(&attr);
}

void* sum_runner(void* arg)
{
    long long* limit_ptr = (long long *) arg;
    long long limit = *limit_ptr;//Derefrencing
    for(long long i=0; i<=limit; i++)
        sum += i;
    printf("Sum is %lld \n", sum);
    pthread_exit(0);
}

void ping()
{
  puts("Ping");
  def = PONG;
}

void pong()
{
  puts("Pong");
  def = PING;
}

pthread_t * all_thread(pthread_t *t_id)
{
  t_id = malloc(sizeof(pthread_t));
  return t_id;
}

int main(int argc, char **argv)
{
    if(argc<2)
    {
    puts("Usage ./objFile <num 1> <num 2> .. <num n>"); 
        exit(1);
    }

    int args = argc-1;
    long long limit = atoll(argv[1]);
    def = PING;

   struct threads_util *threads[args];

   for (int i=0; i<args; i++)
    threads[i]->t_id = all_thread(threads[i]->t_id);
    puts("In");    
   for(int i=0; i<args; i++)
   {
      threads[i]->init_attr = init_attr_fn;

      threads[i]->init_attr(threads[i]->attr);
      pthread_create(threads[i]->t_id,threads[i]->attr,sum_runner,&limit);
   }

    //Begin -Main Functions
    for(int i=0; i<= 10; i++)
    {
    if(def == PING)
           ping();
        else if(def == PONG)
           pong();
        else
           puts("UNKOWN PI-PO");           
    }
    //End - Main Functions

    for(int i=0; i<args; i++)
    {
      pthread_join(threads[i]->t_id,NULL);
    }
}

You can see i have a puts("In"), in the main function, just after the for loop when i call all_thread args times. Well calling the function argc times with the for loop according to my debugging skills, is the problem. And also before we did all the allocation strategy, I had a problem on calling the thread function, of course resulting in a Segmentation Fault. threads[i]->init_attr(threads[i]->attr); . Help would be very much appreciated.

Answer 1

struct threads_util *threads[args];

means that you define an array of pointers to struct threads_util . But you don't actually create any struct threads_util so this line:

threads[i]->t_id = all_thread(threads[i]->t_id);

is illegal as it writes to memory not allocated.

You need to allocate memory for struct threads_util first:

for (int i=0; i<args; i++)
    threads[i] = malloc(sizeof(struct threads_util));