On 06.08.2017 15:29, Georg Chini wrote:
On 06.08.2017 07:26, Tanu Kaskinen wrote:
On Sat, 2017-08-05 at 21:32 +0200, Georg Chini wrote:
On 05.08.2017 13:37, Tanu Kaskinen wrote:
On Fri, 2017-08-04 at 15:37 +0200, Georg Chini wrote:
This patch adds a new feature to the core which allows to exchange
messages between objects. An object can register/unregister a message
handler with pa_core_message_handler_{register, unregister}() while
any other object can send a message to the handler using the
pa_core_send_message() function. A message has 5 arguments (apart
from passing the core):

recipient: The name of the message handler that will receive the message
message: message command
message_parameters: A string containing additional parameters
message_data: void pointer to some parameter structure, can be used
                as alternative to message_parameters
response: Pointer to a response string that will be filled by the
message handler. The caller is responsible to free the string.

The patch is a precondition for the following patches that also allow
clients to send messages to pulseaudio objects.

Because not every message handler should be visible to clients, a flag
was added to the handler structure which allows to mark a handler as
public or private.

There is no restriction on object names, except that a handler name
always starts with a "/". The intention is to use a path-like syntax,
for example /core/sink_1 for a sink or /name/instances/index for modules.
The exact naming convention still needs to be agreed.

Message groups are also implemented, so that a handler can subscribe
to a message group using pa_core_message_handler_group_[un]subscribe() to receive messages sent to the group. To distinguish group and handler
names, group names lack the leading "/". Some of the code used to
implement the message groups was adapted from hook-list.c. Message
groups are created/deleted implicitely on subscription/unsubscription.

The messaging interface can serve as a full replacement for the current
hook system with several advantages:
- no need to change header files when a new handler/group is implemented
- slightly simpler registration interface
- multi-purpose message handlers that can handle multiple events
- mesage handlers may also be accessible from the client side
We agree that it's good to allow clients to send messages to modules.
Unfortunately, in this patch you're assuming that we'll also replace
hooks with the same system. Can we please keep things simple and do one
change at a time? I'm not enthusiastic about replacing hooks, and I'd
rather move on with the client message passing before getting consensus
on the hook stuff.

For reference, here's a list of unnecessary (from pure client message
passing point of view) things I can gather from the commit message:

- void pointer argument in message handlers
- public/private flag
- message groups (signals would seem like a better fit for the purpose

I wonder if you are at all willing to accept something more general or
are completely focused on the client-only approach. I hoped, that the
features and the two use cases (internal: implementation of signals,
external: message handler to list handlers) could convince you that
the new messaging system is a definite win for pulseaudio even if it
partly duplicates existing functionality.
My current implementation might have drawbacks and problems
that I do not see, but I am willing to put more work into it until those
potential issues are solved. I already pointed out multiple advantages
over existing mechanisms and your categoric denial currently seems
only based on the hook discussion and therefore a bit unfounded to
Meanwhile I have seen a few points where my code seems not general

If you are willing to accept some "versatile message interface", I would
re-work it again. I would then appreciate your additional input regarding

Otherwise I will reluctantly strip it down to what you want because further
discussion seems pointless.
pulseaudio-discuss mailing list

Reply via email to