[pulseaudio-discuss] [PATCH] echo-cancel: Try to minimise in-flight chunks in snapshot latency

[Arun Raghavan]

On Thu, 9 Mar 2017, at 03:27 PM, Georg Chini wrote:
> On 09.03.2017 05:37, Arun Raghavan wrote:
> > We don't always know whether the in-flight memory chunks will be
> > rendered or skipped (if the source is not in RUNNING). This can cause us
> > to have an erroneous estimate of drift, particularly when the canceller
> > starts.
> >
> > To avoid this, we explicitly flush out the send and receive sides of the
> > message queue of audio chunks going from the sink to the source before
> > trying to perform a resync.
> > ---
> >   src/modules/echo-cancel/module-echo-cancel.c | 7 ++++++-
> >   1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/src/modules/echo-cancel/module-echo-cancel.c b/src/modules/echo-cancel/module-echo-cancel.c
> > index dfd05b6..ed75e0c 100644
> > --- a/src/modules/echo-cancel/module-echo-cancel.c
> > +++ b/src/modules/echo-cancel/module-echo-cancel.c
> > @@ -683,8 +683,13 @@ static void do_resync(struct userdata *u) {
> >       pa_log("Doing resync");
> >   
> >       /* update our snapshot */
> > -    source_output_snapshot_within_thread(u, &latency_snapshot);
> > +    /* 1. Get sink input latency snapshot, might cause buffers to be sent to source thread */
> >       pa_asyncmsgq_send(u->sink_input->sink->asyncmsgq, PA_MSGOBJECT(u->sink_input), SINK_INPUT_MESSAGE_LATENCY_SNAPSHOT, &latency_snapshot, 0, NULL);
> > +    /* 2. Pick up any in-flight buffers (and discard if needed) */
> > +    while (pa_asyncmsgq_process_one(u->asyncmsgq))
> > +        ;
> > +    /* 3. Now get the source output latency snapshot */
> > +    source_output_snapshot_within_thread(u, &latency_snapshot);
> >   
> >       /* calculate drift between capture and playback */
> >       diff_time = calc_diff(u, &latency_snapshot);
> 
> While taking a look at the patch I noticed something else in the 
> do_resync().
> You are doing:
> 
>      source_output_snapshot_within_thread(u, &latency_snapshot);
>      pa_asyncmsgq_send(u->sink_input->sink->asyncmsgq, 
> PA_MSGOBJECT(u->sink_input), SINK_INPUT_MESSAGE_LATENCY_SNAPSHOT, 
> &latency_snapshot, 0, NULL);
> 
> from the source thread. I tried something similar in module loopback and
> found that you should not send a message to the sink thread from there.
> 
> At least for bluetooth it looks like input and output is done in the 
> same thread,
> so the pa_asyncmsg_send() will hang. I tested it with my headset and it 
> hangs
> indeed.

Interesting. Do you mean for HSP, or HFP, or ...?

-- Arun