#include <iostream>
#include <atomic>
#include <thread>
#include <mutex>
#include <vector>

using namespace std;

// In this version, rather than synchronize the data,
// we synchronize execution of the code, in particular,
// the increase_mutex method

mutex globalMutex;  // mutex to control exeuction of method

atomic<int> atomic_counter (0);
int unsync_counter = 0;

void increase_atomic(int n) {
  for (int i=0; i<n; ++i)
    ++atomic_counter;
}

void increase_mutex_coarseGrained(int n) {
  lock_guard<mutex> lock(globalMutex);  // safe mutex acquistion
  for (int i=0; i<n; ++i)
    ++unsync_counter;
  // the mutex is released when the lock_guard is destroyed
}

void increase_mutex_fineGrained(int n) {
  for (int i=0; i<n; ++i) {
    lock_guard<mutex> lock(globalMutex);  // safe mutex acquistion
    ++unsync_counter;
  }
}

void waitForThreads(vector<thread> &threads) {
  cout << "wait for all threads..." << endl;
  int joined = 0;
  for (auto & th : threads) {
    th.join();
    joined++;
  }
  threads.clear();
  cout << "join'ed " << joined << " threads" << endl;
}

int main (int argc, char *argv[])
{
  vector<thread> threads;

  auto t1 = chrono::high_resolution_clock::now();
  cout << endl << "increase atomic counter with 10 threads..." << endl;
  for (int i=1; i<=10; ++i)
    threads.push_back(thread(increase_atomic, 10000000));
  waitForThreads(threads);
  cout << "atomic counter: " << atomic_counter << '\n';
  auto t2 = chrono::high_resolution_clock::now();
  cout << chrono::duration_cast<chrono::microseconds>(t2 - t1).count()
       << " microseconds"
       << endl;

  t1 = chrono::high_resolution_clock::now();
  cout << endl << "increase unsynchronized counter with 10 threads, coarse grained..." << endl;
  for (int i=1; i<=10; ++i)
    threads.push_back(thread(increase_mutex_coarseGrained, 10000000));
  waitForThreads(threads);
  cout <<  "unsync counter: " << unsync_counter << '\n';
  t2 = chrono::high_resolution_clock::now();
  cout << chrono::duration_cast<chrono::microseconds>(t2 - t1).count()
       << " microseconds"
       << endl;

  unsync_counter = 0;

  t1 = chrono::high_resolution_clock::now();
  cout << endl << "increase unsynchronized counter with 10 threads, fine grained..." << endl;
  for (int i=1; i<=10; ++i)
    threads.push_back(thread(increase_mutex_fineGrained, 10000000));
  waitForThreads(threads);
  cout <<  "unsync counter: " << unsync_counter << '\n';
  t2 = chrono::high_resolution_clock::now();
  cout << chrono::duration_cast<chrono::microseconds>(t2 - t1).count()
       << " microseconds"
       << endl;

  return 0;
}