Parking place - 3 gates

// Parking sa 3 ulaza.
// Na parking automobili ulaze sa ulaza 0, 1 i 2 po round-robin protokolu
// (jedan udje sa prvog, jedan sa drugog, jedan sa treceg i tako u krug).

// Automobilu se pri stvaranju prosledjuje vreme (u sekundama) koje se on
// zadrzave na parkingu.
// U programu uvek ima jednak broj automobila na svim ulazima!

#include <iostream>
#include <mutex>
#include <thread>
#include <condition_variable>

using namespace std;
using namespace chrono;

class parking {
private:
    mutex m;
    condition_variable na_ulazu[3];
    int sM;
    int aU;
public:
    duration<double, milli> cekao;
   parking() : sM(1), aU(0) {}
   void udji(size_t ulaz)
   {
       unique_lock<mutex> l(m);
       system_clock :: time_point dosao = system_clock :: now();
       while (sM == 0 || aU != ulaz)
        na_ulazu[ulaz].wait(l);
        cekao = system_clock :: now() - dosao;
       --sM;
       aU = (aU+1) % 3;
   }
   void izadji()
   {
       unique_lock<mutex> l(m);
       ++sM;
       na_ulazu[aU].notify_one();
   }
};

mutex term_m;
void automobil(parking& p, size_t ulaz, size_t ostajem_na_parkingu) {
    thread::id id = this_thread::get_id();
    {
        lock_guard<mutex> l(term_m);
        cout<<"Automobil "<<id<<" pokusava da udje na parking na ulaz "<< ulaz<<endl;
    }
    p.udji(ulaz);
    {
        lock_guard<mutex> l(term_m);
        cout<<"Automobil "<<id<<" usao na parking na ulaz "<< ulaz<< " nakon: " << p.cekao.count() << " milisekundi cekanja." << endl;
    }
    this_thread::sleep_for(chrono::seconds(ostajem_na_parkingu));
    p.izadji();
    lock_guard<mutex> l(term_m);
    cout<<"Automobil "<<id<<" izasao sa parkinga."<<endl;
}

const int A = 10;

int main()
{
    parking p;
    thread t[A];

    for (int i=0; i<A; ++i)
        t[i] = thread(automobil, ref(p), i%3, i%2);
    for (int i=0; i<A; ++i)
        t[i].join();

    return 0;
}