[pulseaudio-discuss] pulse audio module callbacks

[Himanshu Chug]

Many thanks Colin, this helped me.

Best Regards,
Himanshu

On Tue, Jun 7, 2011 at 5:17 PM, Colin Guthrie <gmane at colin.guthr.ie> wrote:

> Hello!
>
> 'Twas brillig, and Himanshu Chug at 06/06/11 17:22 did gyre and gimble:
> > I am going through module-cork-music-on-phone.c
> >
> > To understand the code , I need some information about these functions:
>
> Yes, our internal developer docs don't really exist! :s I generally just
> read through the code to see when these call backs are called. It's not
> ideal, but it's pretty straight forward too. That said we really should
> get an effort to provide better internal developer docs (e.g. internal
> APIs within the server).
>
> > 1. when each of these calls backs gets executed/called ?
>
> > sink_input_put_cb
>
> Note that for all these questions you've asked about the function as
> called in module-cork-music-on-phone.c. In reality these functions can
> be called anything you like. The more important question is the HOOK
> that you're attaching them to for which you need to look at the
> pa__init() function in module-cork-music-on-phone.c
>
> PA_CORE_HOOK_SINK_INPUT_PUT
>
> So this hook is called when the sink input (playback stream) is
> physically created. There is an earlier hook that runs called
> PA_CORE_HOOK_SINK_INPUT_NEW which is run before the actual sink input
> object is created.
>
> > sink_input_unlink_cb
>
> PA_CORE_HOOK_SINK_INPUT_UNLINK
>
> This is called when a sink input disappears (e.g. the client application
> closes it's stream (user presses "Stop") or exits.
>
> > sink_input_move_start_cb
>
> PA_CORE_HOOK_SINK_INPUT_MOVE_START
>
> This is called when we start to move a sink input to a new sink. At this
> point the sink input is still attached the sink it is moving from.
>
> > sink_input_move_finish_cb
>
> PA_CORE_HOOK_SINK_INPUT_MOVE_FINISH
>
> This is called when we're done moving a sink input to a new sink and
> thus the sink input is now attached to the sink it was moved to.
>
>
> > 2. these callbacks are internally calling to process() function (given
> > below) , I am interested to understand the last argument pa_bool_t
> > create  of process(struct userdata *u, pa_sink_input *i, pa_bool_t
> create)
> >  ,how to decide when to pass TRUE and FALSE to process? any reference
> > (if available) will be helpful.
>
> You can work this out from the semantics of the descriptions above and
> the code in the process() function itself.
>
> Ultimately it's telling the process method that it should be corking or
> uncorking the streams.
>
> So when we've got a new sink input appearing on our sink (which happens
> in the PUT or MOVE_FINISH hooks), we need to look at (potentially)
> creating a cork on the other sink inputs on that sink, hence a TRUE value.
>
> But when a stream is disappearing (which can happen when it's moved off
> our sink to another one, or when it's just no longer present - i.e.
> UNLINK and MOVE_START hooks), we want to look at uncorking things we
> have previously corked, hence a FALSE value.
>
> > Thanks in advance
>
> Hope that helps.
>
> Col
>
> PS Documentation patches or similar efforts are as welcome as any other
> contribution!
>
> Col
> --
>
> Colin Guthrie
> gmane(at)colin.guthr.ie
> http://colin.guthr.ie/
>
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>
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