Singleton Creation the Thread-safe Way
By Jonathan Ringle, October 01, 1999
Singletons avoid problems with order of construction, at the cost of more problems for multithreading.
October 1999/Singleton Creation the Thread-safe Way/Listing 6
// solution.h
#include "sync.h"
class Singleton
{
public:
static Singleton& instance();
void show_state();
protected:
Singleton();
private:
static Singleton* _instance;
static Critical_Section _key;
int state;
};
Singleton* Singleton::_instance = NULL;
Critical_Section Singleton::_key;
Singleton& Singleton::instance()
{
if(!_instance) // Lock-hint check (Race condition here)
{
Lock_Guard<Critical_Section> gate(_key);
if(!_instance) // Double-check (Race condition resolved)
_instance = new Singleton;
}
return *_instance;
}
