pthread_create int instead of void

Question

I have the following code:

for(i = 0 ; i < max_thread; i++)
{
    struct arg_struct args;
    args.arg1 = file;
    args.arg2 = word;
    args.arg3 = repl;
    if(pthread_create(&thread_id[i],NULL,&do_process,&args) != 0)
    {
        i--;
        fprintf(stderr,RED "\nError in creating thread\n" NONE);
    }
}
for(i = 0 ; i < max_thread; i++)
    if(pthread_join(thread_id[i],NULL) != 0)
    {
        fprintf(stderr,RED "\nError in joining thread\n" NONE);
    }


int do_process(void *arguments)
{
//code missing
}

*How can I transform (void *)do_process into (int) do_process ?*

That function returns very important info and without those returns I don't know how to read the replies

I get the following error: warning: passing arg 3 of `pthread_create' makes pointer from integer without a cast

I don't suppose showing at least the declaration of do_process is a possibility? but aside from that, is there some reason you can't put an arg_result into your args structure and convey your return result with that? — WhozCraig
Put the return value in args and return it. You can interrogate args on its return...use the 2nd param in pthread_join. — Duck
I think it's a great idea. What does second param in pthread_join? I set the value to NULL. — Sam Reina

jxh jxh · Accepted Answer · 2013-08-23T20:23:42

The thread function returns a pointer. At minimum, you can allocate an integer dynamically and return it.

void * do_process (void *arg) {
    /* ... */
    int *result = malloc(sizeof(int));
    *result = the_result_code;
    return result;
}

Then, you can recover this pointer from the thread_join() call;

    void *join_result;
    if(pthread_join(thread_id[i],&join_result) != 0)
    {
        fprintf(stderr,RED "\nError in joining thread\n" NONE);
    } else {
        int result = *(int *)join_result;
        free(join_result);
        /* ... */
    }

pthread_create int instead of void

3 Answers