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

code/7/7.7.is.lock.free.cpp

@@ -0,0 +1,12 @@
+#include <atomic>
+#include <iostream>
+
+struct A {
+    float x;
+    int y;
+    long long z;
+};
+    std::atomic<A> a;
+    std::cout << std::boolalpha << a.is_lock_free() << std::endl;
+    return 0;
+}