[alsa-devel] snd_seq_query_port_subscribers not updating subs index
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 ?
2. Is my fix a correct one or could it leads to other issues ?
Many thanks,
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); } }
- 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.
- Is my fix a correct one or could it leads to other issues ?
It's the correct implementation.
HTH,
Takashi
Sort of, yes
From the snd_seq_query_port_subscribers doc: "To list up all the
subscriptions, call this function with the index numbers from 0 until this returns a negative value."
So does it mean than in certain cases snd_seq_query_port_subscribers increments the index itself, and sometime it does not ?
Thanks, Takashi
On Thu, Apr 12, 2018 at 4:44 PM, Takashi Iwai tiwai@suse.de wrote:
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); } }
- 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.
- Is my fix a correct one or could it leads to other issues ?
It's the correct implementation.
HTH,
Takashi
On Thu, 12 Apr 2018 16:49:27 +0200, Charles Flèche wrote:
Sort of, yes
From the snd_seq_query_port_subscribers doc: "To list up all the
subscriptions, call this function with the index numbers from 0 until this returns a negative value."
So does it mean than in certain cases snd_seq_query_port_subscribers increments the index itself, and sometime it does not ?
It shouldn't increment the index number by itself; at least the kernel interface doesn't do that. But the API doesn't check whether the backend (plugin) didn't touch the returned index value or not, so the possibility is still open :)
Takashi
Thanks, Takashi
On Thu, Apr 12, 2018 at 4:44 PM, Takashi Iwai tiwai@suse.de wrote:
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); } }
- 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.
- Is my fix a correct one or could it leads to other issues ?
It's the correct implementation.
HTH,
Takashi
[2 <text/html; UTF-8 (quoted-printable)>]
On my systems it does increment the index number, and I think I took this code first from code examples of the Alsa doc... I'll make sure to always increment the index by hand.
Thanks again, Takashi
On Thu, Apr 12, 2018 at 4:54 PM, Takashi Iwai tiwai@suse.de wrote:
On Thu, 12 Apr 2018 16:49:27 +0200, Charles Flèche wrote:
Sort of, yes
From the snd_seq_query_port_subscribers doc: "To list up all the
subscriptions, call this function with the index numbers from 0 until
this
returns a negative value."
So does it mean than in certain cases snd_seq_query_port_subscribers increments the index itself, and sometime it does not ?
It shouldn't increment the index number by itself; at least the kernel interface doesn't do that. But the API doesn't check whether the backend (plugin) didn't touch the returned index value or not, so the possibility is still open :)
Takashi
Thanks, Takashi
On Thu, Apr 12, 2018 at 4:44 PM, Takashi Iwai tiwai@suse.de wrote:
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); } }
- 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.
- Is my fix a correct one or could it leads to other issues ?
It's the correct implementation.
HTH,
Takashi
[2 <text/html; UTF-8 (quoted-printable)>]
participants (3)
-
Charles Flèche -
Charles Flèche -
Takashi Iwai