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

code/7/7.6.atomic.cpp

@@ -0,0 +1,19 @@
+#include <atomic>
+#include <thread>
+#include <iostream>
+
+std::atomic<int> count = {0};
+
+int main() {
+    std::thread t1([](){
+        count.fetch_add(1);
+    });
+    std::thread t2([](){
+        count++;        // identical to fetch_add
+        count += 1;     // identical to fetch_add
+    });
+    t1.join();
+    t2.join();
+    std::cout << count << std::endl;
+    return 0;
+}