Singleton class implementation using shared_ptr

Question

#include 
#include 

using namespace std;

class Demo {
    static shared_ptr d;
    Demo(){}
public:    
    static shared_ptr         


        

Answer 1

Some comments from 1 to help with the discussion. Static variable will be destroyed uppon exit of the application, so we don't need to use the smart pointer at this stage as mentioned above.

"If multiple threads attempt to initialize the same static local variable concurrently, the initialization occurs exactly once (similar behavior can be obtained for arbitrary functions with std::call_once).

Note: usual implementations of this feature use variants of the double-checked locking pattern, which reduces runtime overhead for already-initialized local statics to a single non-atomic boolean comparison. (since C++11)

The destructor for a block-scope static variable is called at program exit, but only if the initialization took place successfully. "