oto: use a longer retry budget for AVAudioSessionErrorCodeCannotStartPlaying

This error indicates the app is not active (e.g. backgrounded or in
the middle of an interruption), so it can take noticeably longer to
clear than the other transient AudioQueueStart errors. Bump the retry
budget for this code to ~10s in both newContext and resume, while
keeping the shorter ~2.8s budget for Unspecified and
CannotInterruptOthers. newContext now also uses sleepTime() instead
of a fixed 10ms sleep, resolving the prior TODO.

Updates #93

Author: hajimehoshi

driver_darwin.go

@@ -141,11 +141,15 @@ func newContext(sampleRate int, channelCount int, format mux.Format, bufferSizeI
 		var retryCount int
 	try:
 		if osstatus := _AudioQueueStart(c.audioQueue, nil); osstatus != noErr {
-			if (osstatus == avAudioSessionErrorCodeCannotStartPlaying ||
-				osstatus == avAudioSessionErrorCodeUnspecified) &&
-				retryCount < 100 {
-				// TODO: use sleepTime() after investigating when this error happens.
-				time.Sleep(10 * time.Millisecond)
+			maxRetry := 0
+			switch osstatus {
+			case avAudioSessionErrorCodeCannotStartPlaying:
+				maxRetry = 100
+			case avAudioSessionErrorCodeUnspecified:
+				maxRetry = 30
+			}
+			if retryCount < maxRetry {
+				time.Sleep(sleepTime(retryCount))
 				retryCount++
 				goto try
 			}
@@ -255,10 +259,15 @@ func (c *context) resume() error {
 	var retryCount int
 try:
 	if osstatus := _AudioQueueStart(c.audioQueue, nil); osstatus != noErr {
-		if (osstatus == avAudioSessionErrorCodeCannotStartPlaying ||
-			osstatus == avAudioSessionErrorCodeCannotInterruptOthers ||
-			osstatus == avAudioSessionErrorCodeUnspecified) &&
-			retryCount < 30 {
+		maxRetry := 0
+		switch osstatus {
+		case avAudioSessionErrorCodeCannotStartPlaying:
+			maxRetry = 100
+		case avAudioSessionErrorCodeCannotInterruptOthers,
+			avAudioSessionErrorCodeUnspecified:
+			maxRetry = 30
+		}
+		if retryCount < maxRetry {
 			// It is uncertain that this error is temporary or not. Then let's use exponential-time sleeping.
 			time.Sleep(sleepTime(retryCount))
 			retryCount++