//compile me with gcc pthread.cc -o pthread -lpthread

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>



int num; //global variables visible to both threads

 //declare and initialize mutex lock (global variable)
 pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;


void *procedure( void *);

main() {
int id1 = 0;
int id2 = 1;
//a thread
pthread_t thread;

//pthread_t thread2;

 // Before you create the new thread, init mutex
 pthread_mutex_init(&mutex,  NULL);


//this call creates a thread that starts execution at procedure and takes id1 as argument
pthread_create(&thread, NULL, procedure,  (void *) &id1);

//the original thread calls procedure as well with id2 as argument
procedure(&id2);
//or we could create another thread that calls it
//pthread_create(&thread2, NULL, procedure,  (void *) &id2);

//wait for other thread to finish
pthread_join(thread,NULL);
pthread_mutex_destroy(&mutex);

}

void *procedure(void *arg) {
int threadid = * ((int *)arg);
printf("Thread %d reporting to duty, Sir!\n",threadid);

//we use mutex before accessing the shared num variable.  Try your code with and without the mutex commands
pthread_mutex_lock(&mutex);
num++;
printf("Number was %d, Sir!\n",num);
//dont forget to unlock to let the other thread in
pthread_mutex_unlock(&mutex);
}