/*
     File: LockFreeFIFO.h
 Abstract: Part of CoreAudio Utility Classes
  Version: 1.2
 
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*/
#include <libkern/OSAtomic.h>

template <class ITEM>
class LockFreeFIFOWithFree
{
	LockFreeFIFOWithFree(); // private, unimplemented.
public:
	LockFreeFIFOWithFree(UInt32 inMaxSize)
		: mReadIndex(0), mWriteIndex(0), mFreeIndex(0)
	{
		//assert(IsPowerOfTwo(inMaxSize));
		mItems = new ITEM[inMaxSize];
		mMask = inMaxSize - 1;
	}
	
	~LockFreeFIFOWithFree()
	{
		delete [] mItems;
	}

	
	void Reset() 
	{
		FreeItems();
		mReadIndex = 0;
		mWriteIndex = 0;
		mFreeIndex = 0;
	}
	
	ITEM* WriteItem() 
	{
		//printf("WriteItem %d %d\n", mReadIndex, mWriteIndex);
		FreeItems(); // free items on the write thread.
		UInt32 nextWriteIndex = (mWriteIndex + 1) & mMask;
		if (nextWriteIndex == mFreeIndex) return NULL;
		return &mItems[mWriteIndex];
	}
	
	ITEM* ReadItem() 
	{
		//printf("ReadItem %d %d\n", mReadIndex, mWriteIndex);
		if (mReadIndex == mWriteIndex) return NULL;
		return &mItems[mReadIndex];
	}
	void AdvanceWritePtr() { OSAtomicCompareAndSwap32(mWriteIndex, (mWriteIndex + 1) & mMask, (int32_t*)&mWriteIndex); }
	void AdvanceReadPtr()  { OSAtomicCompareAndSwap32(mReadIndex,  (mReadIndex  + 1) & mMask, (int32_t*)&mReadIndex); }
private:
	ITEM* FreeItem() 
	{
		if (mFreeIndex == mReadIndex) return NULL;
		return &mItems[mFreeIndex];
	}
	void AdvanceFreePtr() { OSAtomicCompareAndSwap32(mFreeIndex, (mFreeIndex + 1) & mMask, (int32_t*)&mFreeIndex); }
	
	void FreeItems() 
	{
		ITEM* item;
		while ((item = FreeItem()) != NULL)
		{
			item->Free();
			AdvanceFreePtr();
		}
	}
	
	volatile UInt32 mReadIndex, mWriteIndex, mFreeIndex;
	UInt32 mMask;
	ITEM *mItems;
};



// Same as above but no free.

template <class ITEM>
class LockFreeFIFO
{
	LockFreeFIFO(); // private, unimplemented.
public:
	LockFreeFIFO(UInt32 inMaxSize)
		: mReadIndex(0), mWriteIndex(0)
	{
		//assert(IsPowerOfTwo(inMaxSize));
		mItems = new ITEM[inMaxSize];
		mMask = inMaxSize - 1;
	}
	
	~LockFreeFIFO()
	{
		delete [] mItems;
	}
	
	void Reset() 
	{
		mReadIndex = 0;
		mWriteIndex = 0;
	}
	
	ITEM* WriteItem() 
	{
		UInt32 nextWriteIndex = (mWriteIndex + 1) & mMask;
		if (nextWriteIndex == mReadIndex) return NULL;
		return &mItems[mWriteIndex];
	}
	
	ITEM* ReadItem() 
	{
		if (mReadIndex == mWriteIndex) return NULL;
		return &mItems[mReadIndex];
	}
	
		// the CompareAndSwap will always succeed. We use CompareAndSwap because it calls the PowerPC sync instruction,
		// plus any processor bug workarounds for various CPUs.
	void AdvanceWritePtr() { OSAtomicCompareAndSwap32(mWriteIndex, (mWriteIndex + 1) & mMask, (UInt32*)&mWriteIndex); }
	void AdvanceReadPtr()  { OSAtomicCompareAndSwap32(mReadIndex,  (mReadIndex  + 1) & mMask, (UInt32*)&mReadIndex); }
	
private:
	
	volatile UInt32 mReadIndex, mWriteIndex;
	UInt32 mMask;
	ITEM *mItems;
};

