C++(17)：shared

C++14通过shared_timed_mutex提供了读写锁，而C++17通过shared_mutex提供了读写锁。

说实话，除了shared_timed_mutex可以在lock时传递一个timeout_duration作为最长等待时间，本人还没没弄清楚这两个读写锁在使用上有什么明显的区别：

#include 
#include 
#include 
#include 
using namespace std;

shared_mutex sLock;
int g_data = 10;

unsigned long getTime()
{
	return chrono::system_clock::now().time_since_epoch().count()/chrono::system_clock::period::den;
}

void read_shared_data(int id)
{
	cout << getTime() << " thread "<< id << " begin" << endl;
	shared_lock slk(sLock);
	cout << getTime() << " thread " << id << " read data=" << g_data << endl;
}

int main()
{
	shared_lock slk(sLock);              //读锁加锁
	cout << getTime() << " shared_lock locked"< ulk(sLock);              //写锁加锁
	cout << getTime() << " unique_lock locked"<