验证C++ map返回引用的线程安全问题

现象：没出现线程安全问题。

结论：这么写是线程安全的。 

// ConsoleApplication12.cpp : 此文件包含 "main" 函数。程序执行将在此处开始并结束。
//
#include 
#include 

#include 

using namespace std;

class spin_lock
{
public:
    spin_lock()
    {}
    void lock()
    {
        _mutex.lock();
    }
    void unlock()
    {
        _mutex.unlock();
    }
private:
    std::mutex _mutex;
};

class auto_lock
{
public:
    auto_lock(spin_lock* lock)
    {
        _lock = lock;
        _lock->lock();
    }

    ~auto_lock()
    {
        _lock->unlock();
    }
private:
    spin_lock* _lock;
};



spin_lock m_lock;

struct A
{
    int a;
    int b;
    std::string c;
    char d[1024];
};

class my_hash_map
{
public:
    std::unordered_map m;

    A& operator[] (const int& k)
    {
        auto_lock lock(&m_lock);
        return m[k];
    }


    bool erase(const int& k)
    {
        auto_lock lock(&m_lock);
        return m.erase(k);
    }

public:
};

my_hash_map m;

void f()
{
    m[0].a = -1;
    while (1)
    {
        for (int i = 0; i < 1000000; ++i)
        {
            if (m[0].a != -1)
            {
                cout << "=========================   m[0].a != -1" << endl;
            }
        }
        cout << "--" << endl;
    }
}

int main()
{
    std::thread t = thread(f);
    while (1)
    {
        for (int i = 1; i < 1000000; ++i)
        {
            m[i].a = i - 1;
        }
        for (int i = 1; i < 1000000; ++i)
        {
            m.erase(i);
        }
    }

    return 0;
}