mutex_lock2.cpp

#include<pthread.h>
#include<stdio.h>
#include<unistd.h>
void *fun1();
void *fun2();
 int shared=1; //shared variable
 pthread_mutex_t l; //mutex lock
 int main()
 {
 pthread_mutex_init(&l, NULL); //initializing mutex locks
 pthread_t thread1, thread2;
 pthread_create(&thread1, NULL, fun1, NULL);
 pthread_create(&thread2, NULL, fun2, NULL);
 pthread_join(thread1, NULL);
 pthread_join(thread2,NULL);
 printf("Final value of shared is %d\n",shared); //prints the last updated value of shared variable
 }
 void *fun1()
 {
     int x;
     printf("Thread1 trying to acquire lock\n");
     pthread_mutex_lock(&l); //thread one acquires the lock. Now thread 2 will not be able to acquire the lock //until it is unlocked by thread 1
    printf("Thread1 acquired lock\n");
     x=shared;//thread one reads value of shared variable
     printf("Thread1 reads the value of shared variable as %d\n",x);
     x++;  //thread one increments its value
     printf("Local updation by Thread1: %d\n",x);
     sleep(1);  //thread one is preempted by thread 2
     shared=x; //thread one updates the value of shared variable
     printf("Value of shared variable updated by Thread1 is: %d\n",shared);
     pthread_mutex_unlock(&l);
     printf("Thread1 released the lock\n");
 }
void *fun2()
 {
     int y;
     printf("Thread2 trying to acquire lock\n");
     pthread_mutex_lock(&l);
     printf("Thread2 acquired lock\n");
     y=shared;//thread two reads value of shared variable
     printf("Thread2 reads the value as %d\n",y);
     y--;  //thread two increments its value
     printf("Local updation by Thread2: %d\n",y);
     sleep(1); //thread two is preempted by thread 1
     shared=y; //thread one updates the value of shared variable
     printf("Value of shared variable updated by Thread2 is: %d\n",shared);
     pthread_mutex_unlock(&l);
     printf("Thread2 released the lock\n");
 }