[alsa-devel] snd_seq_query_port_subscribers not updating subs index

[Takashi Iwai]

On Sun, 08 Apr 2018 18:37:58 +0200,
Charles Flèche wrote:
> 
> Hi all,
> 
> I'm iterating through subscribers with snd_seq_query_port_subscribers to
> disconnect them. It works most of the time, but when a2j (an alsa -> jack
> MIDI bridge) runs, snd_seq_query_port_subscribers does not update the subs
> index, and the next call returns 0, leading to an infinite loop. I have to
> manually increase the index when the disconnection fails (meaning that I
> hit an a2j connection).
> 
> while (snd_seq_query_port_subscribers(seq, subs) >= 0) {
>   addr = *snd_seq_query_subscribe_get_addr(subs);
>   if (snd_seq_disconnect_to(seq, port, addr.client, addr.port) < 0) {
>     snd_seq_query_subscribe_set_index(subs,
> snd_seq_query_subscribe_get_index(subs) + 1);
>   }
> }
> 
> 1. Is the non-updated subs index an expected behavior ?

Sort of, yes.  It's no iterator operation like query_next_client.
It just queries the given index and fills out the result.  The user
needs to iterate with incrementing the index manually.

> 2. Is my fix a correct one or could it leads to other issues ?

It's the correct implementation.


HTH,

Takashi