issue with Threadsafe singleton with semaphore

Question

I have written a simple singleton application.

The following is my sample main class

// ThreadsafeSingletonUsingSemaphore.cpp : Defines the entry poi         


        

Answer 1

You don't need to write all of that code. The easiest way to implement a threadsafe singleton is to use Scott Meyer's singleton idiom:

class Singleton {
    int counter;
    mutable std::mutex counter_guard;
    Singleton() {}
public:
    Singleton(const Singleton&) = delete;
    Singleton(Singleton&&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    Singleton& operator=(Singleton&&) = delete;

    static Singleton& instance() {
        static Singleton theInstance;
        return theInstance;
    }

    void setCounter(int newVal) {
        std::unique_lock lock(counter_guard);
        counter = newVal;
    }  
    void incrementCounter() {
        std::unique_lock lock(counter_guard);
        ++counter;
    }  
    int getCounter() const {
        std::unique_lock lock(counter_guard);
        return counter;
    }  
};

---

An even easier way would be to use a std::atomic type for the counter member variable. Then the mutex and lock guards can be omitted at all.