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// 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;

}