Posix Threads with Mutex - multithreading

Question

I have started working on POSIX threads. I wrote a simple code.
My question is on Mutex.
Initializing the mutex inside threaded function gives wrong result. While initializing the mutex inside main function (before creation of threads) gives proper result. Why is that happening?
The count value is expected to be 200000 but it is showing some improper value < 200000.
Here is my code.
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <malloc.h>
void *thread_handler (void *name);
unsigned long int count=0;
pthread_mutex_t lock;
void main () {
pthread_t thread_num[2];
pthread_attr_t attr;
pthread_attr_init (&attr);
int i;
for (i=0;i<2;i++) {
if (pthread_create (&thread_num[i],&attr,(void *) thread_handler,NULL)<0) {
printf ("\n Error in Creating the Threads");
}
}
for (i=0;i<2;i++) {
pthread_join(thread_num[i],NULL); //Waiting for the Thread to Exit
}
printf ("\n The value of count=%ld\n",count);
}
void *thread_handler (void *arg) {
int i;
if (pthread_mutex_init (&lock,NULL)!=0) {
printf ("\n Error in Initializing the Mutex");
}
pthread_mutex_lock (&lock);
for (i=0;i<100000;i++) {
count++;
}
pthread_mutex_unlock(&lock);
pthread_exit(NULL);
}
Thanks in Advance,
NDPrasad.

Answer 1

When you initialize the mutex inside the thread_handler function, it is initialized twice(because you create two threads that execute this function). It causes undefined behavior(which means that anything can happen).
A quote from here:
Attempting to initialize an already initialized mutex results in undefined behavior.