Why still use AAudioServiceEndpointMMAP even setting shared mode

[xzhan96]

Hi @philburk

I see the android source code here https://cs.android.com/android/platform/superproject/main/+/refs/heads/main:frameworks/av/services/oboeservice/AAudioEndpointManager.cpp;l=147;bpv=0;bpt=0

It is explicitly that if use AAUDIO_SHARING_MODE_SHARED, an AAudioServiceEndpointShared is created and used.
However, when debugging in my phones, Xiaomi- MI 9 and Oneplus 8(IN2010), I got below logs shows AAudioServiceEndpointMMAP is used.

2023-08-11 15:52:41.514 20617-20617 AudioStreamBuilder com.mobileer.oboetester I rate = 0, channels = 0, format = 5, sharing = SH, dir = INPUT
2023-08-11 15:52:41.514 20617-20617 AudioStreamBuilder com.mobileer.oboetester I device = 0, sessionId = -1, perfMode = 12, callback: ON with frames = 0
2023-08-11 15:52:41.514 20617-20617 AudioStreamBuilder com.mobileer.oboetester I usage = 0, contentType = 2, inputPreset = 6, allowedCapturePolicy = 0
2023-08-11 15:52:41.514 20617-20617 com.mobileer.oboetester D PlayerBase::PlayerBase()
2023-08-11 15:52:41.517 920-11114 audioserver D PlayerBase::PlayerBase()
2023-08-11 15:52:41.518 920-11114 APM_AudioPolicyManager audioserver D getInputForAttr() source 6, samplingRate 48000, format 0x1, channelMask 0xc, session 5593, flags 0x10 attributes={ Content type: AUDIO_CONTENT_TYPE_MUSIC Usage: AUDIO_USAGE_UNKNOWN Source: AUDIO_SOURCE_VOICE_RECOGNITION Flags: 0x100 Tags: }
2023-08-11 15:52:41.520 920-11114 AudioPolic...agerCustom audioserver V getPackageName: No packages for calling UID
2023-08-11 15:52:41.520 770-770 audio_hw_primary android.hardware.audio@2.0-service D adev_open_input_stream is_karaoke_fastcapture=0
2023-08-11 15:52:41.520 770-770 audio_hw_primary android.hardware.audio@2.0-service D adev_open_input_stream: enter: sample_rate(48000) channel_mask(0xc) devices(0x80000004) stream_handle(0xe8682a00) io_handle(2366) source(6) format 1
2023-08-11 15:52:41.520 770-770 audio_hw_primary android.hardware.audio@2.0-service D adev_open_input_stream is_karaoke_fastcapture=1(mmap)
2023-08-11 15:52:41.520 770-770 audio_hw_utils android.hardware.audio@2.0-service W audio_extn_utils_update_stream_input_app_type_cfg: App type could not be selected. Falling back to default
2023-08-11 15:52:41.522 920-8262 AudioFlinger audioserver I AudioFlinger's thread 0x79378ec800 tid=8262 ready to run
2023-08-11 15:52:41.524 920-11114 APM_AudioPolicyManager audioserver D getInputForAttr() returns input 2366 type 0 selectedDeviceId 18 for port ID 1543
2023-08-11 15:52:41.524 920-11114 AAudioServ...dpointMMAP audioserver D open() mMapClient.uid = 1041, pid = 920 => portHandle = 1543
2023-08-11 15:52:41.524 920-11114 AAudioServ...dpointMMAP audioserver D open() deviceId = 18, sessionId = -1

Then I see this logic

It seems force use AAUDIO_SHARING_MODE_EXCLUSIVE and then call mStreamInternal->open(builder) again through Binder, this maybe why use AAudioServiceEndpointMMAP finnally.

My question is why design like this? what the real purpose of AAudioServiceEndpointShared?

Thanks a lot.

[philburk]

The EXCLUSIVE stream is used to play the output of the mixer.

There can be multiple SHARED mode streams. They all get mixed together in AAudioServiceEndpointPlay::callbackLoop()
That mixed results has to be output somehow.

What is an easy way to output a single stream? Call AAudio and open an EXCLUSIVE stream.
All the code I needed already existed. So there was no need to write new code to pass data from the mixer to the MMAP buffer.

call mStreamInternal->open(builder) again through Binder,

No. When running in the service, we bypass Binder and just call the appropriate service routines directly.

[xzhan96]

Thanks a lot, understood.