#include<iostream>
#include<thread>
#include<mutex>
#include<ctime>
#include <semaphore.h>

using namespace std;
using namespace std::this_thread;
using namespace std::chrono;

int readcount=0; 
sem_t read_mutex, wrt;

 void read(int id){
     sem_wait(&read_mutex);

     readcount++;	
    if (readcount == 1)    sem_wait(&wrt);

    sem_post (&read_mutex);

    cout<<"reader"<<id<<"reading is performed"<<endl;
    sleep_for(seconds(2));

    sem_wait(&read_mutex);
    readcount--;

    	if(readcount == 0) sem_post(&wrt);

	sem_post(&read_mutex);
 }
 
void write(int id){

       sem_wait(&wrt);

         cout<<"writer"<<id<<"writing is performed"<<endl;
         sleep_for(seconds(4));

      sem_post(&wrt);

}
int main(){
    sem_init(&read_mutex,0,1);
	sem_init(&wrt,0,1);
	thread t1(read, 0);
    thread t2(write, 0);
	thread t3(read, 1);
    thread t4(write, 1);
	t1.join(); t2.join();t3.join();t4.join();
}