c passing several arguments to threads - c

Question

when i create a thread, i want to pass several arguments.
So i define in a header file the following:
struct data{
char *palabra;
char *directorio;
FILE *fd;
DIR *diro;
struct dirent *strdir;
};
In a .c file i do the following
if (pthread_create ( &thread_id[i], NULL, &hilos_hijos, ??? ) != 0){
perror("Error al crear el hilo. \n");
exit(EXIT_FAILURE);
}
How do i pass all this arguments to the threads. I though about:
1) first use malloc to allocate memory for this structure and then give each parameter a value:
struct data *info
info = malloc(sizeof(struct data));
info->palabra = ...;
2) define
struct data info
info.palabra = ... ;
info.directorio = ...;
and then, how do i access these parameters in the thread
void thread_function ( void *arguments){
???
}
thanks in advance

Answer 1

Here is a working (and relatively small) example:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
/*
* To compile:
* cc thread.c -o thread-test -lpthread
*/
struct info {
char first_name[64];
char last_name[64];
};
void *thread_worker(void *data)
{
int i;
struct info *info = data;
for (i = 0; i < 100; i++) {
printf("Hello, %s %s!\n", info->first_name, info->last_name);
}
}
int main(int argc, char **argv)
{
pthread_t thread_id;
struct info *info = malloc(sizeof(struct info));
strcpy(info->first_name, "Sean");
strcpy(info->last_name, "Bright");
if (pthread_create(&thread_id, NULL, thread_worker, info)) {
fprintf(stderr, "No threads for you.\n");
return 1;
}
pthread_join(thread_id, NULL);
return 0;
}

Answer 2

Do not use option #2. The data structure could be overwritten (explicitly, for instance using the same structure to start another thread, or implicitly, for instance having it overwritten on the stack). Use option #1.
To get at your data, at the start of your thread, do
struct data *info = (struct data*)arguments;
Then access info as normal. Make sure to free it when the thread is done (or, as I prefer, have the caller free it after joining with the thread).

Answer 3

Create a pointer to a struct like you do in the first case above:
//create a pointer to a struct of type data and allocate memory to it
struct data *info
info = malloc(sizeof(struct data));
//set its fields
info->palabra = ...;
info->directoro = ...;
//call pthread_create casting the struct to a `void *`
pthread_create ( &thread_id[i], NULL, &hilos_hijos, (void *)data);

Answer 4

1) you need to use malloc and not define like below
struct data *info;
info = (struct data *)malloc(sizeof(struct data));
and pass the pointer of the structure in ptherad call as below
pthread_create ( &thread_id[i], NULL, &thread_fn, (void *)info );
2) you can access them in thread function as below
void thread_function ( void *arguments){
struct data *info = (struct data *)arguments;
info->....
}