====== Using mutex in pthread to access a shared variable ======

<code c pthread-mutex-shared-var.c>
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

// Global variable and mutex
int shared_variable = 0;
pthread_mutex_t mutex;

// Function to be executed by threads
void *update_shared_variable(void *arg) {
    pthread_mutex_lock(&mutex);   // Lock the access to the variable
    shared_variable++;           // Update the shared variable
    printf("Updated value: %d\n", shared_variable);
    pthread_mutex_unlock(&mutex); // Unlock the access to the variable
    pthread_exit(NULL);
}

int main() {
    pthread_t thread1, thread2;

    // Initialize the mutex
    pthread_mutex_init(&mutex, NULL);

    // Create the threads
    pthread_create(&thread1, NULL, update_shared_variable, NULL);
    pthread_create(&thread2, NULL, update_shared_variable, NULL);

    // Wait for the threads to finish
    pthread_join(thread1, NULL);
    pthread_join(thread2, NULL);

    // Destroy the mutex
    pthread_mutex_destroy(&mutex);

    return 0;
}
</code>

The program demonstrates the use of a mutex to synchronize access to a shared variable between multiple threads. \\ It uses pthreads for creating threads and a mutex to ensure that only one thread can access and modify the shared variable at a time.

**Global Variable and Mutex**: A global integer shared_variable and a mutex mutex are defined.

**Thread Function**: update_shared_variable locks the mutex before accessing the shared variable, increments it, prints the updated value, and then unlocks the mutex.

**Main Function**: Initializes the mutex, creates two threads that run update_shared_variable, waits for these threads to complete, and finally destroys the mutex.