[pulseaudio-discuss] RFC: Public API for managing nodes

[Tanu Kaskinen]

On Tue, 2013-08-06 at 14:42 +0200, David Henningsson wrote:
> On 08/06/2013 02:30 PM, Tanu Kaskinen wrote:
> > On Tue, 2013-08-06 at 13:26 +0200, David Henningsson wrote:
> >> On 08/05/2013 01:37 PM, Tanu Kaskinen wrote:
> >>> On Wed, 2013-07-17 at 12:26 +0200, David Henningsson wrote:
> >>>> On 07/17/2013 11:22 AM, Tanu Kaskinen wrote:
> >>>>> On Wed, 2013-07-17 at 09:27 +0200, David Henningsson wrote:
> >>>>>> On 07/16/2013 03:20 PM, Tanu Kaskinen wrote:
> >>>>>>> What operations do you mean? Moving or removing a default connection is
> >>>>>>> not supported as such, but if the client tries that anyway, we can
> >>>>>>> implicitly convert the connection to an explicit one and disable default
> >>>>>>> connections, or we can require the client to do these operations
> >>>>>>> explicitly, but I think the latter would be too inconvenient for the
> >>>>>>> client.
> >>>>>>
> >>>>>> Ok, I think I didn't read the proposal well enough. Having done that, I
> >>>>>> understand that you're suggesting a global switch "default connections
> >>>>>> on/off" only. Or is it a per-node switch?
> >>>>>
> >>>>> It is a per-node switch.
> >>>>>
> >>>>>> I have another idea that might be worth considering: how about that the
> >>>>>> "explicit" layer can both enable and disable connections? So that there
> >>>>>> could be a default connection between A and B, but there is also some
> >>>>>> sort of explicit override that disables it. This would be more flexible
> >>>>>> than a more global on/off switch.
> >>>>>
> >>>>> I'm not sure what you mean. Do you perhaps mean that the default
> >>>>> connection on/off switch should be per-node (which it already is in my
> >>>>> proposal), or that it should be per-connection (so that if there are
> >>>>> multiple default from node A, it's possible to disable only a subset of
> >>>>> those)?
> >>>>>
> >>>>> I didn't make make it possible to disable individual default
> >>>>> connections, because I had a feeling that it would have very messy
> >>>>> semantics. If default connection from A to B is disabled, what is the
> >>>>> routing code supposed to do when conditions change and the default
> >>>>> routing is re-evaluated? Can it ever reactivate the connection between A
> >>>>> and B again? Is the per-connection disabling handled as a blacklist of
> >>>>> connections that must never be automatically activated?
> >>>>
> >>>> If the A -> B route is explicitly_disabled, that overrides any default 
> >>>> connections the routing system tries to make.
> >>>
> >>> What is the use case for explicitly disabled connections? I'll assume
> >>> here that your idea was to allow moving a default connection elsewhere
> >>> (making the connection explicit in the process) without disabling all
> >>> default connections for the node.
> >>>
> >>> When the user moves a default connection, the routing system obviously
> >>> shouldn't immediately create another default connection elsewhere to
> >>> replace the disabled connection.
> >>>
> >>> On the other hand, if the routing system doesn't create replacement
> >>> connections, then that results in weird behaviour. Let's say that
> >>> there's a default connection A -> B, and the user moves the connection
> >>> to A -> C. Then B disappears. The routing changes its opinion of the
> >>> best available routing for A, which might be D. So removing node B
> >>> resulted in audio suddenly appearing in node D, even though nothing was
> >>> playing to B.
> >>>
> >>
> >> Assume your example of a default connection A -> B which the user
> >> changes into A -> C, by adding an explicit A -> C connection. Without
> >> some sort of explicitly_disabled blacklist that would then include A ->
> >> B, the routing system would be free to route A to *both* B and C.
> > 
> > My solution is that the application disables the default routing
> > altogether for A, if it doesn't want to have the default connection A ->
> > B. It seems to me that this causes fewer surprises than the blacklisting
> > approach.
> > 
> >> Whether this is implemented as a bool flag or as a separate blacklist is
> >> an implementation detail, but a bool flag just seemed simpler and faster
> >> to me, than having to look in several lists to figure out whether a
> >> connection exists or not.
> > 
> > You don't need to look in several lists to figure out whether a
> > connection exists or not. If we have connection objects, which I think
> > we both want to have, it's enough to get the list all connections and
> > see whether a particular connection is included in that list.
> > 
> 
> Okay, so let me see if I understand this right. You propose that you can
> add explicit connections between two specified nodes, but blacklisting
> default connections have to be done on a node wide level (rather than
> per connection).
> 
> That sounds interesting, as it would be more resilient towards nodes
> appearing and disappearing later on.
> I think that blacklisting would have to be two booleans per node though,
> one for outgoing connections and one for incoming. And a connection
> cannot exist if it is blocked on *either* side, rather than both sides.
> Does that make sense?

My plan has so far been to only disable outgoing default connections,
but if there's need for it, I don't see any problem with adding another
bool for disabling incoming default connections. Do you have a use case?

-- 
Tanu