pThreads分段错误

Question

This is the struct passed to thread declaration:

   typedef struct  {
              int rowsPerThread;                    
              int StartingRow;                     
              double co[WIDTH][HEIGHT][2];          
              uint64_t total_iters;                

      } thdata;

And here's how I use it: (notice the malloc)

  /* data passed to each thread */
  thdata *data[threads_num];


  /* create threads */
  for (i=0; i<threads_num; i++)
  {
      data[i]=(thdata *)malloc(sizeof(thdata));
      data[i]->rowsPerThread= rowsPerThread;
      data[i]->StartingRow= i*rowsPerThread;

      for (i=i*rowsPerThread; i<rowsPerThread; i++)
      memcpy(data[i]->co[i], Coordinates[i], sizeof (Coordinates) * HEIGHT * 2);


      pthread_create(&thread[i], NULL, (void *) &threaded_calc, (void *) &data[i]);   
      free(data[i]);
  }

I think there's a problem with the malloc().

It gives me segmentation fault.

Answer 1

The problem is that you free your data[i] in the for block, right after creation of a pthread and since you cannot know when the thread is started, it may be possible that data[i] is freed before the thread is effectively started by the scheduler .

So, you should call free inside the thread body.