std 3a 3amutex

1#include <iostream>
2#include <map>
3#include <string>
4#include <chrono>
5#include <thread>
6#include <mutex>
7 
8std::map<std::string, std::string> g_pages;
9std::mutex g_pages_mutex;
10 
11void save_page(const std::string &url)
12{
13    // simulate a long page fetch
14    std::this_thread::sleep_for(std::chrono::seconds(2));
15    std::string result = "fake content";
16 
17    std::lock_guard<std::mutex> guard(g_pages_mutex);
18    g_pages[url] = result;
19}
20 
21int main() 
22{
23    std::thread t1(save_page, "http://foo");
24    std::thread t2(save_page, "http://bar");
25    t1.join();
26    t2.join();
27 
28    // safe to access g_pages without lock now, as the threads are joined
29    for (const auto &pair : g_pages) {
30        std::cout << pair.first << " => " << pair.second << '\n';
31    }
32}