Single case getinstance in C + + () use double lock to improve efficiency __c++

Original code:

singleclass* singleclass::getinstance ()
{
	mutex.lock ()
	if (_singleclass = = nullptr)
	{
		_ Singleclass = new _singleclass ();
	}
		Mutex.unlock ();
		return _singleclass;;
}

Std:::lock_guard<std::mutex> Locker (Parameters (Locker)) >

In the code above because the code only needs to be new once _singleclass ()

So every time you use a lock, you're wasting your resources.

So change the code to look like the following

singleclass* singleclass::getinstance ()
{
	if (_singleclass = = nullptr)
	{	
		mutex.lock ()
		if ( _singleclass = = nullptr)
		_singleclass = new _singleclass ();
	}
		Mutex.unlock ();
		return _singleclass;;
}

This will return directly to _singleclass after creating the completion instance; And no further locks are added.

This will return directly to _singleclass after creating the completion instance; And no further locks are added.