tree f90b707e5384f86dcac2bb4f746587afd720cb04
parent a30d95acf60f04531923e8ab06d976744697bf51
author Zhihai Xu <zhihaixu@google.com> 1380487333 -0700
committer Zhihai Xu <zhihaixu@google.com> 1380487333 -0700

Failure to start playback on A2DP sink after connection

This is what happen:
after Headset is connected, we call start_audio_datapath which will send AVDTP_Start command to Headset,
Headset reject it with bad state. Bluedroid stack will ack failure to start_audio_datapath.
The next time we write audio data to bluetooth, we will call start_audio_datapath again to send AVDTP_Start command to Headset
Headset reject it with bad state again. Bluedroid stack will ack failure to start_audio_datapath.
When the third time we call start_audio_datapath, right at that time we receive  AVDTP_Start command from Headset.
Handle AVDTP_Start command and Handle start_audio_datapath are in two different threads.
Handle AVDTP_Start command is in btu_task thread.
Handle start_audio_datapath() is in btif_task thread.
We have race condition in this case
Because when  btif_task processed BTIF_AV_START_STREAM_REQ_EVT(triggered by start_audio_datapath),
it don't know we receive  AVDTP_Start command which is processed in  btu_task.
btif_task will send a message BTA_AV_API_START_EVT to btu_task, which will be handled by bta_av_do_start.
AVDTP_start command from headset is handled by bta_av_start_ok.
bta_av_start_ok will send BTA_AV_START_EVT with suspending true to btif_task and send AVDTP_Suspend command
to headset to suspend the AVDTP for reconfiguration purpose.

in bta_av_do_start, we will check whether the AVDTP is already started, we will know the AVDTP is already start at this time because
bta_av_do_start is also running in btu_task. We will send BTA_AV_START_EVT with success to btif_task.

In the btif_task, BTA_AV_START_EVT will be processed by btif_av_state_opened_handler:
For the first BTA_AV_START_EVT with suspending true sent by bta_av_start_ok, it will ignore it:
if ((p_av->start.status == BTA_SUCCESS) && (p_av->start.suspending == TRUE))
               return TRUE;
For the second BTA_AV_START_EVT with success sent by bta_av_do_start , it will ack success to start_audio_datapath, and change to
BTIF_AV_STATE_STARTED/BTAV_AUDIO_STATE_STARTED, after receive success ack from bluedroid stack, we will start send Audio data to bluetooth.

At last we received  AVDTP_Suspend response accept from Headset, we will send BTA_AV_SUSPEND_EVT to btif_task, which will be
handled by btif_av_state_started_handler. It will call btif_a2dp_on_suspended and call audio_state_cb  with new audio state
BTAV_AUDIO_STATE_STOPPED.
so The state between bluedroid stack and audio data path is out of sync.
The fix is to send failure message if we know we suspend AVDTP in bta_av_do_start,
also make sure we won't miss acknowledgement for pending start if we exit opened state,
to avoid audio data path dead lock.

bug:10953908
Change-Id: I1704839977324b7c4e234eb843cddf3719e10d2c