PublicUtility/CARingBuffer.h

/*
     File: CARingBuffer.h 
 Abstract:  Part of CoreAudio Utility Classes  
  Version: 1.2.2 
  
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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];
    UInt32 mTimeBoundsQueuePtr;
};
 
 
 
#endif