see #2: update std::atomic and memory model

code/7/7.8.relaxed.cpp

@@ -0,0 +1,21 @@
+#include <atomic>
+#include <thread>
+#include <vector>
+#include <iostream>
+
+std::atomic<int> counter = {0};
+
+int main() {
+    std::vector<std::thread> vt;
+    for (int i = 0; i < 100; ++i) {
+        vt.emplace_back([](){
+            counter.fetch_add(1, std::memory_order_relaxed);
+        });
+    }
+
+    for (auto& t : vt) {
+        t.join();
+    }
+    std::cout << "current counter:" << counter << std::endl;
+    return 0;
+}