Resolves issue with multiple calls to audio unit initialization

webrtc/modules/audio_device/ios/audio_device_ios.mm

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 68 matching lines @@
 // VerifyAudioParametersForActiveAudioSession() for a mismatch between the
 // preferred number of channels and the actual number of channels.
 const int kPreferredNumberOfChannels = 1;
 // Number of bytes per audio sample for 16-bit signed integer representation.
 const UInt32 kBytesPerSample = 2;
 // Hardcoded delay estimates based on real measurements.
 // TODO(henrika): these value is not used in combination with built-in AEC.
 // Can most likely be removed.
 const UInt16 kFixedPlayoutDelayEstimate = 30;
 const UInt16 kFixedRecordDelayEstimate = 30;
+// Calls to AudioUnitInitialize() can fail if called back-to-back on different
+// ADM instances. A fall-back solution is to allow multiple sequential calls
+// with as small delay between each. This factor sets the max number of allowed
+// initialization attempts.
+const int kMaxNumberOfAudioUnitInitializeAttempts = 5;
+
 
 using ios::CheckAndLogError;
 
 // Verifies that the current audio session supports input audio and that the
 // required category and mode are enabled.
 static bool VerifyAudioSession(AVAudioSession* session) {
   LOG(LS_INFO) << "VerifyAudioSession";
   // Ensure that the device currently supports audio input.
   if (!session.isInputAvailable) {
     LOG(LS_ERROR) << "No audio input path is available!";
@@ skipping 635 matching lines @@
   LOGI() << "SetupAndInitializeVoiceProcessingAudioUnit";
   RTC_DCHECK(!vpio_unit_) << "VoiceProcessingIO audio unit already exists";
   // Create an audio component description to identify the Voice-Processing
   // I/O audio unit.
   AudioComponentDescription vpio_unit_description;
   vpio_unit_description.componentType = kAudioUnitType_Output;
   vpio_unit_description.componentSubType = kAudioUnitSubType_VoiceProcessingIO;
   vpio_unit_description.componentManufacturer = kAudioUnitManufacturer_Apple;
   vpio_unit_description.componentFlags = 0;
   vpio_unit_description.componentFlagsMask = 0;
+
   // Obtain an audio unit instance given the description.
   AudioComponent found_vpio_unit_ref =
       AudioComponentFindNext(nullptr, &vpio_unit_description);
 
   // Create a Voice-Processing IO audio unit.
   OSStatus result = noErr;
   result = AudioComponentInstanceNew(found_vpio_unit_ref, &vpio_unit_);
   if (result != noErr) {
     vpio_unit_ = nullptr;
     LOG(LS_ERROR) << "AudioComponentInstanceNew failed: " << result;
@@ skipping 115 matching lines @@
                                 kAudioOutputUnitProperty_SetInputCallback,
                                 kAudioUnitScope_Global, input_bus,
                                 &input_callback, sizeof(input_callback));
   if (result != noErr) {
     DisposeAudioUnit();
     LOG(LS_ERROR) << "Failed to specify the input callback on the input bus: "
                   << result;
   }
 
   // Initialize the Voice-Processing I/O unit instance.
+  // Calls to AudioUnitInitialize() can fail if called back-to-back on
+  // different ADM instances. The error message in this case is -66635 which is
+  // undocumented. Tests have shown that calling AudioUnitInitialize a second
+  // time, after a short sleep, avoids this issue.
+  // See webrtc:5166 for details.
+  int failed_initalize_attempts = 0;
   result = AudioUnitInitialize(vpio_unit_);
-  if (result != noErr) {
-    result = AudioUnitUninitialize(vpio_unit_);
-    if (result != noErr) {
-      LOG_F(LS_ERROR) << "AudioUnitUninitialize failed: " << result;
-    }
-    DisposeAudioUnit();
+  while (result != noErr) {
     LOG(LS_ERROR) << "Failed to initialize the Voice-Processing I/O unit: "
                   << result;
-    return false;
+    ++failed_initalize_attempts;
+    if (failed_initalize_attempts == kMaxNumberOfAudioUnitInitializeAttempts) {
+      // Max number of initialization attempts exceeded, hence abort.
+      LOG(LS_WARNING) << "Too many initialization attempts";
+      DisposeAudioUnit();
+      return false;
+    }
+    LOG(LS_INFO) << "pause 100ms and try audio unit initialization again...";
+    [NSThread sleepForTimeInterval:0.1f];
+    result = AudioUnitInitialize(vpio_unit_);
   }
+  LOG(LS_INFO) << "Voice-Processing I/O unit is now initialized";
   return true;
 }
 
 bool AudioDeviceIOS::RestartAudioUnitWithNewFormat(float sample_rate) {
   LOGI() << "RestartAudioUnitWithNewFormat(sample_rate=" << sample_rate << ")";
   // Stop the active audio unit.
   LOG_AND_RETURN_IF_ERROR(AudioOutputUnitStop(vpio_unit_),
                           "Failed to stop the the Voice-Processing I/O unit");
 
   // The stream format is about to be changed and it requires that we first
@@ skipping 177 matching lines @@
   // Read decoded 16-bit PCM samples from WebRTC (using a size that matches
   // the native I/O audio unit) to a preallocated intermediate buffer and
   // copy the result to the audio buffer in the |io_data| destination.
   SInt8* source = playout_audio_buffer_.get();
   fine_audio_buffer_->GetPlayoutData(source);
   memcpy(destination, source, dataSizeInBytes);
   return noErr;
 }
 
 }  // namespace webrtc