text: /*
       File: CARingBuffer.h
   Abstract: Part of CoreAudio Utility Classes
    Version: 1.1
   
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  */
  #if !defined(__COREAUDIO_USE_FLAT_INCLUDES__)
  	#include <CoreAudio/CoreAudioTypes.h>
  #else
  	#include <CoreAudioTypes.h>
  #endif
  
  
  #ifndef CARingBuffer_Header
  #define CARingBuffer_Header
  
  enum {
  	kCARingBufferError_OK = 0,
  	kCARingBufferError_TooMuch = 3, // fetch start time is earlier than buffer start time and fetch end time is later than buffer end time
  	kCARingBufferError_CPUOverload = 4 // the reader is unable to get enough CPU cycles to capture a consistent snapshot of the time bounds
  };
  
  typedef SInt32 CARingBufferError;
  
  const UInt32 kGeneralRingTimeBoundsQueueSize = 32;
  const UInt32 kGeneralRingTimeBoundsQueueMask = kGeneralRingTimeBoundsQueueSize - 1;
  
  class CARingBuffer {
  public:
  	typedef SInt64 SampleTime;
  
  	CARingBuffer();
  	~CARingBuffer();
  	
  	void					Allocate(int nChannels, UInt32 bytesPerFrame, UInt32 capacityFrames);
  								// capacityFrames will be rounded up to a power of 2
  	void					Deallocate();
  	
  	CARingBufferError	Store(const AudioBufferList *abl, UInt32 nFrames, SampleTime frameNumber);
  							// Copy nFrames of data into the ring buffer at the specified sample time.
  							// The sample time should normally increase sequentially, though gaps
  							// are filled with zeroes. A sufficiently large gap effectively empties
  							// the buffer before storing the new data. 
  							
  							// If frameNumber is less than the previous frame number, the behavior is undefined.
  							
  							// Return false for failure (buffer not large enough).
  				
  	CARingBufferError	Fetch(AudioBufferList *abl, UInt32 nFrames, SampleTime frameNumber);
  								// will alter mNumDataBytes of the buffers
  	
  	CARingBufferError	GetTimeBounds(SampleTime &startTime, SampleTime &endTime);
  	
  protected:
  
  	int						FrameOffset(SampleTime frameNumber) { return (frameNumber & mCapacityFramesMask) * mBytesPerFrame; }
  
  	CARingBufferError		ClipTimeBounds(SampleTime& startRead, SampleTime& endRead);
  	
  	// these should only be called from Store.
  	SampleTime				StartTime() const { return mTimeBoundsQueue[mTimeBoundsQueuePtr & kGeneralRingTimeBoundsQueueMask].mStartTime; }
  	SampleTime				EndTime()   const { return mTimeBoundsQueue[mTimeBoundsQueuePtr & kGeneralRingTimeBoundsQueueMask].mEndTime; }
  	void					SetTimeBounds(SampleTime startTime, SampleTime endTime);
  	
  protected:
  	Byte **					mBuffers;				// allocated in one chunk of memory
  	int						mNumberChannels;
  	UInt32					mBytesPerFrame;			// within one deinterleaved channel
  	UInt32					mCapacityFrames;		// per channel, must be a power of 2
  	UInt32					mCapacityFramesMask;
  	UInt32					mCapacityBytes;			// per channel
  	
  	// range of valid sample time in the buffer
  	typedef struct {
  		volatile SampleTime		mStartTime;
  		volatile SampleTime		mEndTime;
  		volatile UInt32			mUpdateCounter;
  	} TimeBounds;
  	
  	CARingBuffer::TimeBounds mTimeBoundsQueue[kGeneralRingTimeBoundsQueueSize];
      volatile UInt32 mTimeBoundsQueuePtr;
  };
  
  
  
  #endif
  