Create threadsafe_impl.cpp

singleton/threadsafe_impl.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <mutex>
+#include <future>
+
+using namespace std;
+std::mutex m;
+
+class S{
+public:
+    static S& getInstance() {
+        std::lock_guard<std::mutex> mylock(m);
+        if (s == nullptr)
+            s = new S();
+        return *s;
+    }
+private:
+    S() = default;
+    ~S() = default;
+    S(const S&) = delete;
+    S& operator=(const S&) = delete;
+    static S *s;
+};
+
+S* S::s = nullptr;
+
+void Instance() {
+    S::getInstance();
+}
+
+int main()
+{
+    auto f1 = std::async(std::launch::async, Instance);
+    auto f2 = std::async(std::launch::async, Instance);
+    auto f3 = std::async(std::launch::async, Instance);
+
+    f1.get();
+    f2.get();
+    f3.get();
+
+    return 0;
+}