CODEWITHSUNDEEP
c++multithreading
MagnusHimmler
MagnusHimmler

Reputation: 65

how to lock a member function of a class which uses a constructor with an initialisation list

Here is an excellent piece of code that addresses how to use a lock on member functions of an object.

 #include <thread>
 #include <mutex>
 #include <iostream>

 class Foo
 {
 public:
      void increment()
      {
         for ( int i = 0; i < 10000000; ++i )
         {
             std::lock_guard<std::mutex> lock(mtx); //lock mtx
              ++x;

             // mtx is automatically released when lock
             // goes out of scope -> RAII
         }
     }

     void decrement()
     {
           for ( int i = 0; i < 10000000; ++i )
           {
               std::lock_guard<std::mutex> lock(mtx); //lock mtx
               --x;

              // mtx is automatically released when lock
              // goes out of scope -> RAII
          }
        }

        static int x;
        static std::mutex mtx;
  };

   int Foo::x = 0;
   std::mutex Foo::mtx;

   int main()
   {
       std::thread t1(&Foo::increment, Foo());
       std::thread t2(&Foo::decrement, Foo());

       t1.join();
       t2.join();

       std::cout << Foo::x;
    }

My question is, how to implement this if the constructor has a data member initialization list. Is it possible?

Upvotes: 0

Views: 589

Answers (1)

Nikita
Nikita

Reputation: 6427

You don't need an additional lock if Foo has data member initialization list as each thread has it's own instance of Foo class. Member initialization list specifies the initializers for direct and virtual base subobjects and non-static data members.

You only need a lock to control the consistence of state shared between threads. Like static Foo::x in your sample.

Upvotes: 1

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