POSIX parent/child threads not sharing data - c

Question

One final question for the evening. I have a homework question that I cannot seem to solve, and after spending the better part of the night on it, I'll ask it here.
The problem is a program that is to calculate the Fibonacci sequence given an integer input at the command line (./foo.out 15, for example, and it will calculate the first 15 Fibonacci numbers). The additional parameters are as follows:
1.) It must use two POSIX threads, a parent thread and a child thread.
2.) It must share data (an array) between them.
Currently, the function is breaking when program control passes back to the parent thread. All I am getting is a completely non-descriptive segfault. As can be seen below, I have it outputting at every possible change in control.
Code:
#include <stdio.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>
void *fibonacci(void *param, int numbers[]);
void *runner(void *param);
int main(int argc, char *argv[])
{
pthread_t tid;
pthread_attr_t attr;
if ( argc != 2)
{
fprintf(stderr, "Usage: 426.out <integer value> \n");
return -1;
}
if (atoi(argv[1]) < 0)
{
fprintf(stderr, "Argument must be non-negative\n");
return -2;
}
pthread_attr_init(&attr);
pthread_create(&tid, &attr, runner, argv[1]);
pthread_join(tid,NULL);
return 0;
}
void *fibonacci(void *param, int numbers[])
{
int it, IT_MAX;
printf("Entering Child Thread:\n");
IT_MAX = atoi(param);
numbers[0] = 0;
numbers[1] = 1;
for (it = 2; it < IT_MAX; ++it)
{
numbers[it] = (numbers[it - 1] + numbers[it - 2]);
}
for (it = 0; it < IT_MAX; ++it)
{
printf("%d\n", numbers[it]);
}
printf("Exiting Child Function.\n");
}
void *runner(void *param)
{
int it, IT_MAX;
int numbers[IT_MAX];
pthread_t tid;
pthread_attr_t attr;
printf("Entering Parent Thread:\n");
pthread_attr_init(&attr);
pthread_create(&tid, &attr, fibonacci(param, numbers), NULL);
pthread_join(tid, NULL);
IT_MAX = atoi(param);
for (it = 0; it < IT_MAX; it++)
{
printf("%d\n", numbers[it]); // I suspect the program breaks here
// It produces a segfault rather than this
}
printf("Leaving Parent Thread\n");
}
The question I have, if it is not clear from above, is what am I doing wrong. I am using gcc, and have been using the -Wall -Werror and -lpthread. -Werror keeps throwing "Control Structure going to end of non-void function", but nothing has anything to say about what can be causing the segfault. As before, I looked for the last hour for a question or article that addresses this, so if this is a dupe, please point me to the question or article in which it is addressed. Thanks to anyone in advance for their help.

Answer 1

One of your problems is in this line:
pthread_create(&tid, &attr, fibonacci(param, numbers), NULL);
Instead of starting a thread with the fibonacci() function, this calls the fibbonacci() function in the current thread and passes the result to pthread_create() as the thread start function. fibonacci() doesn't return a function pointer, so this new thread will crash the program.
You need to just pass fibonacci as the third parameter.
Futhermore, fibonacci() must be declared as void *fibonacci(void *) in order to be used as a thread start function. If you want to pass two parameters, you'll need to place them into a struct and pass a pointer to that.
This pair of lines is also problematic:
int it, IT_MAX;
int numbers[IT_MAX];
IT_MAX is an uninitialised variable, and you use it here to define the size of the numbers[] array. That could also be leading to your crash.

Answer 2

This line
pthread_create(&tid, &attr, fibonacci(param, numbers), NULL);
does not pass the address of fibonacci() to pthread_create() but calls fibonacci(param, numbers)and passes the result returned to pthread_create() as 3rd argument.