spinlock in c++11 based on atomic_flag

spinlock.h

#ifndef _SPINLOCK_H_20170410_
#define _SPINLOCK_H_20170410_

#include <atomic>

class spinlock {
public:
    spinlock() { m_lock.clear(); }
    spinlock(const spinlock&) = delete;
    ~spinlock() = default;

    void lock() {
        while (m_lock.test_and_set(std::memory_order_acquire));
    }
    bool try_lock() {
        return !m_lock.test_and_set(std::memory_order_acquire);
    }
    void unlock() {
        m_lock.clear(std::memory_order_release);
    }
private:
    std::atomic_flag m_lock;
};

#endif//_SPINLOCK_H_20170410_

spinlock_test.cpp

#include "spinlock.h"
#include <mutex>
#include <future>
#include <iostream>
#include <map>

spinlock lock;
int value = 0;

int loop(bool inc, int limit) {
    std::cout << "Started " << inc << " " << limit << std::endl;
    for (int i = 0; i < limit; ++i) {
        std::unique_lock<spinlock> _lock(lock);
        if (inc)
            ++value;
        else
            --value;
    }
    return 0;
}

int main() {
    auto f = std::async(std::launch::async, std::bind(loop, true, 20000000));
    loop(false, 10000000);
    f.wait();
    std::cout << value << std::endl;
}