//
// 7.3.critical.section.b.cpp
// chapter 7 parallelism and concurrency
// modern c++ tutorial
//
// created by changkun at changkun.de
// https://github.com/changkun/modern-cpp-tutorial
//

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

int v = 1;

void critical_section(int change_v) {
 static std::mutex mtx;
 std::unique_lock<std::mutex> lock(mtx);
 // do contention operations
 v = change_v;
 std::cout << v << std::endl;
 // release the lock
 lock.unlock();

 // during this period,
 // others are allowed to acquire v

 // start another group of contention operations
 // lock again
 lock.lock();
 v += 1;
 std::cout << v << std::endl;
}

int main() {
 std::thread t1(critical_section, 2), t2(critical_section, 3);
 t1.join();
 t2.join();
 return 0;
}