Swapable variables

Useful Tools and Components
1

Just a small code that I use for some swapable variables, such as audio or other things that I want to mess with while everything is running. EG: load a new audio while the previous audio is still playing, no interruptions.

Please, if you find this stupid be nice and explain why so I can learn. :wink: Iā€™m a very old ā€œguruā€ programmer, but I suffer from mental problems, so sometimes I miss the little thingsā€¦

Hereā€™s an example on how I would use this for audio. I declare:

WusikSwapable originalAudio;

Now I get get the current playiung one with

originalAudio.getCurrent();

And the other one with

originalAudio.getOther();

When Iā€™m ready to swamp each other I call

originalAudio.readyToSwap();

And in the processor block, before anything else I call

originalAudio.check();

This way I can load something to the next buffer without disrupting the audio and while keeping a copy of the previous buffer at all times and also while having just one code to handle how the audio plays.

template <class WType>
class WusikSwapable
{
public:
	WusikSwapable() 
	{ 
		current = 0;
		swap = false;
	};
	//
	void readyToSwap() { swap = true; }
	//
	WType& getCurrent()
	{
		return variables[current];
	}
	//
	WType& getOther()
	{
		return variables[1 - current];
	}
	//
	bool check()
	{
		if (swap)
		{
			current = 1 - current;
			swap = false;
			return true;
		}
		//
		return false;
	}
	//
	bool getSwap() { return swap; }
	//
private:
	WType variables[2];
	int current;
	bool swap;
};
2

Whatā€™s wrong with std::swap?

std::unique_ptr<MyNewComplexObject> newObject = createNewObject();

{
    SpinLock::ScopedLockType sl(lock); // Or whatever type of locking mechanism you use...
    std::swap(newObject, currentlyUsedObject);
}

// the old object will get deleted here.
3

Well, it doesnā€™t do what my code does, and doesnā€™t do what I need. :wink: As I said, letā€™s say I have some Audio Buffer that has the audio I want to playback. With my class above I can just add another audio, mark to be swaped when possible, and everything just works. std:swap just swaps a pointer, totally useless for my needs.

Cheers, WilliamK

4

But this means that youā€™re checking the variable in every render callback, which adds unnecessary branching. If youā€™re using lots of objects this might add some non-trivial performance overhead.

The other solution has absolutely no branching overhead, the only performance risk is a priority inversion for the short period of time while the lock is held by another thread for the swap operation.

5

Yeah, indeed, thanks. But, for my case is just two variables Iā€™m using, and not often, so it should be ok.

6

I would rather use a local scoped shared_ptr that copy the member one during the process call so it has itā€™s own copy.
And you could switch the member one directly.
Still you need to have a custom dtor for this shared_ptr with a delete pool so the delete is not done in the audio thread