/*  gcc -o program program.c -lpthread  */ 


#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <sys/types.h>
#include <unistd.h>
#include <pthread.h> /* POSIX threads */

void *mythread(void *);	/* prototype of thread routine */ 
int sharedVar=1234 ;			/* global variable */ 


int main() {
   pthread_t tid;      

   pthread_create(&tid, NULL, mythread, NULL);

   printf("\n Main: created thread %d. sharedVar=%d \n", tid%1000, sharedVar); 

   pthread_yield(); /* yield to another thread */ 

   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 
   printf("\n Main: sharedVar now is %d.\n", sharedVar);    pthread_yield(); 
 

 pthread_join(tid, NULL);

 exit(0);

}


/******************/
/* thread routine */
/******************/

void *mythread (void *arg) 
{   int pid;

   /* display the value of the global variable */ 
    printf("\n thread %lu: sharedVar now is %d.\n", pthread_self()%1000, sharedVar); 
    sharedVar = 1111;
    printf("\n thread %lu: sharedVar now is %d.\n", pthread_self()%1000, sharedVar); 

    pthread_yield(); /* yield to another thread or main */ 

 pid = fork(); /* create a child process */
 if ( pid == 0 )  /* child code begins */
 {
   printf("\n CHILD in thread: sharedVar= %d.\n", sharedVar); 
 
   pthread_yield(); /* yield to another thread */ 

   sharedVar = 1122;
   printf("\n CHILD in thread: sharedVar= %d.\n", sharedVar);    pthread_yield();

   sharedVar = 1133;
   printf("\n CHILD in thread: sharedVar= %d.\n", sharedVar);    pthread_yield();

   sharedVar = 1144;
   printf("\n CHILD in thread: sharedVar= %d.\n", sharedVar);    pthread_yield();

   sharedVar = 1155;
   printf("\n CHILD in thread: sharedVar= %d.\n", sharedVar);    pthread_yield();


   printf("CHILD:  DONE\n");
 }

 if ( pid > 0 )  /* PARENT CODE */
 { 
   printf("\n PARENT in thread: sharedVar= %d.\n", sharedVar); 

   sharedVar = 5555;
   printf("\n PARENT in thread: sharedVar= %d.\n", sharedVar); 

   pthread_yield(); /* yield to another thread */ 

   printf("\n PARENT in thread: sharedVar= %d.\n", sharedVar); 

   pthread_yield(); /* yield to another thread */ 

   sharedVar = 5577;
   printf("\n PARENT in thread: sharedVar= %d.\n", sharedVar); 

   pthread_yield(); /* yield to another thread */ 
 }

    /* thread exit with an integer */ 
    pthread_exit (216); 
}