efficient thread-safe singleton in C++

Question

The usual pattern for a singleton class is something like

static Foo &getInst()
{
  static Foo *inst = NULL;
  if(inst == NULL)
    inst = new Foo(...);
         


        

Answer 1

Your alternative is called "double-checked locking".

There could exist multi-threaded memory models in which it works, but POSIX does not guarantee one