added drogon

.gitmodules

@@ -1,3 +1,6 @@
 [submodule "parallel-hashmap"]
 	path = third_party/parallel-hashmap
 	url = https://github.com/greg7mdp/parallel-hashmap
+[submodule "drogon"]
+	path = third_party/drogon
+	url = https://github.com/an-tao/drogon

CMakeLists.txt

@@ -12,3 +12,7 @@ set(CMAKE_CXX_FLAGS_RELEASE "-O3")
 add_executable(${PROJECT_NAME} main.cpp)
 
 target_include_directories(${PROJECT_NAME} PUBLIC include)
+target_include_directories(${PROJECT_NAME} PUBLIC third_party)
+
+add_subdirectory(third_party/drogon)
+target_link_libraries(${PROJECT_NAME} PRIVATE drogon)   

include/user.hpp

@@ -8,6 +8,10 @@ private:
     uint_fast64_t balance;
     std::string password;
 
+    //for read/write of object's state concurrently
+    std::mutex bal_lock;
+    std::mutex pass_lock;
+
 public:
     /**
      * @brief User constructor
@@ -26,6 +30,7 @@ public:
 
     bool ChangePassword(const std::string &attempt, std::string &&new_pass)
     {
+        std::lock_guard<std::mutex> lock{pass_lock};
         const bool state = (password == attempt);
         if (state)
         {
@@ -45,7 +50,14 @@ public:
      */
     static bool SendFunds(User &a, User &b, uint_fast64_t amount, const std::string &attempt)
     {
-        const bool state = (a.password == attempt) && (a.balance >= amount);
+        bool state;
+        {
+            std::lock_guard<std::mutex> lock{a.pass_lock};
+            state = (a.password == attempt);
+        }
+
+        std::scoped_lock<std::mutex, std::mutex> lock{a.bal_lock, b.bal_lock};
+        state = state && (a.balance >= amount);
         if (state)
         {
             a.balance -= amount;
@@ -59,8 +71,9 @@ public:
      * 
      * @return the balance
      */
-    uint_fast64_t GetBal() const
+    uint_fast64_t GetBal()
     {
+        std::lock_guard<std::mutex> lock{bal_lock};
         return balance;
     }
 
@@ -70,8 +83,9 @@ public:
      * @param attempt the password
      * @return wether the passwords match
      */
-    bool VerifyPassword(const std::string &attempt) const
+    bool VerifyPassword(const std::string &attempt) //for connected services
     {
+        std::lock_guard<std::mutex> lock{pass_lock};
         return (password == attempt);
     }
 };

third_party/drogon

@@ -0,0 +1 @@
+Subproject commit a19d0427ed1fe80f40e5d4d2c8450a48c807be20