Tars的单件，加锁, 双check机制, 保证正确和效率，有点意思

static T *getInstance()

{

//加锁, 双check机制, 保证正确和效率

if(!_pInstance)

{

TC_ThreadLock::Lock lock(_tl);

if(!_pInstance)

{

if(_destroyed)

{

LifetimePolicy<T>::deadReference();

_destroyed = false;

}

_pInstance = CreatePolicy<T>::create();

LifetimePolicy<T>::scheduleDestruction((T*)_pInstance, &destroySingleton);

}

}

return (T*)_pInstance;

}