Function newContext

driver_darwin.go:92–161

(sampleRate int, channelCount int, format mux.Format, bufferSizeInBytes int)

var theContext *context

func newContext(sampleRate int, channelCount int, format mux.Format, bufferSizeInBytes int) (*context, chan struct{}, error) {
	// defaultOneBufferSizeInBytes is the default buffer size in bytes.
	//
	// 12288 seems necessary at least on iPod touch (7th) and MacBook Pro 2020.
	// With 48000[Hz] stereo, the maximum delay is (12288*4[buffers] / 4 / 2)[samples] / 48000 [Hz] = 100[ms].
	// '4' is float32 size in bytes. '2' is a number of channels for stereo.
	const defaultOneBufferSizeInBytes = 12288

	var oneBufferSizeInBytes int
	if bufferSizeInBytes != 0 {
		oneBufferSizeInBytes = bufferSizeInBytes / bufferCount
	} else {
		oneBufferSizeInBytes = defaultOneBufferSizeInBytes
	}
	bytesPerSample := channelCount * 4
	oneBufferSizeInBytes = oneBufferSizeInBytes / bytesPerSample * bytesPerSample

	ready := make(chan struct{})

	c := &context{
		cond:                 sync.NewCond(&sync.Mutex{}),
		mux:                  mux.New(sampleRate, channelCount, format),
		oneBufferSizeInBytes: oneBufferSizeInBytes,
	}
	theContext = c

	if err := initializeAPI(); err != nil {
		return nil, nil, err
	}

	go func() {
		runtime.LockOSThread()
		defer runtime.UnlockOSThread()

		var readyClosed bool
		defer func() {
			if !readyClosed {
				close(ready)
			}
		}()

		q, bs, err := newAudioQueue(sampleRate, channelCount, oneBufferSizeInBytes)
		if err != nil {
			c.err.TryStore(err)
			return
		}
		c.audioQueue = q
		c.unqueuedBuffers = bs

		var retryCount int
	try:
		if osstatus := _AudioQueueStart(c.audioQueue, nil); osstatus != noErr {
			if osstatus == avAudioSessionErrorCodeCannotStartPlaying && retryCount < 100 {
				// TODO: use sleepTime() after investigating when this error happens.
				time.Sleep(10 * time.Millisecond)
				retryCount++
				goto try
			}