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AudioRingBuffer2.h

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#ifndef __AudioRingBuffer2_h__
#define __AudioRingBuffer2_h__

#include <CoreAudio/CoreAudioTypes.h>
#include <Carbon/Carbon.h> // for CompareAndSwap

/*
        This class implements an audio ring buffer. Multi-channel data can be either
        interleaved or deinterleaved.
*/

enum {
        kAudioRingBufferError_WayBehind = -2, // both fetch times are earlier than buffer start time
        kAudioRingBufferError_SlightlyBehind = -1, // fetch start time is earlier than buffer start time (fetch end time OK)
        kAudioRingBufferError_OK = 0,
        kAudioRingBufferError_SlightlyAhead = 1, // fetch end time is later than buffer end time (fetch start time OK)
        kAudioRingBufferError_WayAhead = 2, // both fetch times are later than buffer end time
        kAudioRingBufferError_TooMuch = 3, // fetch start time is earlier than buffer start time and fetch end time is later than buffer end time
        kAudioRingBufferError_CPUOverload = 4 // the reader is unable to get enough CPU cycles to capture a consistent snapshot of the time bounds
};

typedef SInt32 AudioRingBufferError;

const UInt32 kTimeBoundsQueueSize = 32;
const UInt32 kTimeBoundsQueueMask = kTimeBoundsQueueSize - 1;

class AudioRingBuffer {
public:
        typedef SInt64 SampleTime;

        AudioRingBuffer();
        ~AudioRingBuffer();

        void                                    Allocate(int nChannels, UInt32 bytesPerFrame, UInt32 capacityFrames);
                                                                // capacityFrames will be rounded up to a power of 2
        void                                    Deallocate();

        AudioRingBufferError    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).

        AudioRingBufferError    Fetch(AudioBufferList *abl, UInt32 nFrames, SampleTime frameNumber);

        AudioRingBufferError    GetTimeBounds(SampleTime &startTime, SampleTime &endTime);

protected:

        int                                             FrameOffset(SampleTime frameNumber) { return (frameNumber & mCapacityFramesMask) * mBytesPerFrame; }

        AudioRingBufferError    CheckTimeBounds(SampleTime startRead, SampleTime endRead);

        // these should only be called from Store.
        SampleTime                              StartTime() const { return mTimeBoundsQueue[mTimeBoundsQueuePtr & kTimeBoundsQueueMask].mStartTime; }
        SampleTime                              EndTime()   const { return mTimeBoundsQueue[mTimeBoundsQueuePtr & kTimeBoundsQueueMask].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;

        AudioRingBuffer::TimeBounds mTimeBoundsQueue[kTimeBoundsQueueSize];
        UInt32 mTimeBoundsQueuePtr;
};

#endif // __AudioRingBuffer2_h__

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